research article photocatalytic activity and optical...

Research ArticlePhotocatalytic Activity and Optical Properties of Blue PersistentPhosphors under UV and Solar Irradiation

C R Garciacutea12 L A Diaz-Torres1 J Oliva1 M T Romero2 and P Salas3

1Laboratorio de Fotocatalisis y Fotosıntesis Artificial Centro de Investigaciones en Optica AP 1-948 37150 Leon GTO Mexico2Facultad de Ciencias Fısico Matematicas Universidad Autonoma de Coahuila Camporredondo 25000 Saltillo COAH Mexico3Centro de Fısica Aplicada y Tecnologıa Avanzada Universidad Nacional Autonoma de Mexico AP 1-101076000 Juriquilla QRO Mexico

Correspondence should be addressed to L A Diaz-Torres ditlaciociomx

Received 25 February 2016 Revised 12 June 2016 Accepted 25 July 2016

Academic Editor Meenakshisundaram Swaminathan

Copyright copy 2016 C R Garcıa et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Blue phosphorescent strontium aluminosilicate powders were prepared by combustion synthesis route and a postannealingtreatments at different temperatures X-ray diffraction analysis showed that phosphors are composed of two main hexagonalphases SrAl

2O4and Sr

3Al32O51 The morphology of the phosphors changed from micrograins (1000∘C) to a mixture of bars and

hexagons (1200∘C) and finally to only hexagons (1300∘C) as the annealing temperature is increased Photoluminescence spectrashowed a strong blue-green phosphorescent emission centered at 120582em = 455 nm which is associated with 4f65d1 rarr 4f6 (8S

72)

transition of the Eu2+ The sample annealed at 1200∘C presents the highest luminance value (40 Cdm2) with CIE coordinates(01589 01972) Also the photocatalytic degradation of methylene blue (MB) under UV light (at 365 nm) was monitored Samplesannealed at 1000∘C and 1300∘C presented the highest percentage of degradation (32 and 385 resp) after 360min In the caseof photocatalytic activity under solar irradiation the samples annealed at 1000∘C 1150∘C and 1200∘C produced total degradationof MB after only 300min Hence the results obtained with solar photocatalysis suggest that our powders could be useful for watercleaning in water treatment plants

1 Introduction

Long persistent phosphor (LPP) materials have severalapplications such as emergency signals in the darknesswall painting radiation detection displays lamps and dec-orations [1] Due to their importance the developmentof new LPP with stable chemical and physical proper-ties is still a challenge in the field of materials scienceLong persistent SrAl

2O4Eu2+Dy3+ (510 nm) phosphors have

shown high brightness lasting for 10 h [2 3] Similarlyblue phosphorescent emission at around 120582em = 450 nmhas been obtained from CaAl

2O4Eu2+Nd3+ (430 nm)

SrMgSi2O6Dy3+ (455 nm) and BaMgAl

10O17Eu2+Co3+

(450 nm) systems [1 4] Nonetheless these systems showedless brightness and time of phosphorescence than those forthe green SrAl

2O4Eu2+Dy3+ phosphor Thus the develop-

ment of newblue LPPsmaterials with blue emission at around450 nm is required for the applications mentioned above

Besides few reports have demonstrated the use of theLPPs in the photocatalysis area It has been proposed thatthe mixture of LPPs and photocatalyst composites can helpto improve the photocatalytic process under ultraviolet (UV)light excitation The photocatalystLPP composites such asTiO2SrAl2O4Eu2+Dy3+ have been proposed to enhance

the benzene oxidation under UV light or in the darkness[5] Another composite Ti

2minusxNyO2CaAl2O4Eu2+Dy3+ was

used to decompose gaseous acetaldehyde or nitrogen oxideacetaldehyde by a self-fluorescence assisted in the dark [6]Another composite Ag

3PO4Sr4Al14O25(EuDy) decom-

posed the Rhodamine B without light assistance [7] Herethe photocatalyst Ag

3PO4is excited by the light emitted

from the LPP after turning off the UV excitation which wasmaintained during 30minutes this produced the degradationof rhodamine dissolved in an aqueous solution [7] then andfew studies about the photocatalytic properties of LPPs havebeen published

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2016 Article ID 1303247 8 pageshttpdxdoiorg10115520161303247

2 International Journal of Photoenergy

The utilization of LPPs for photocatalytic applications hasbeen attractive because the phosphorescent materials haveelectrons with high mobility from the valence band (VB)levels to the traps levels which can act as electrons storageand this fact can favor the photocatalytic properties [8]Thesetraps levels are usually generated by oxygen vacancy defectsor impurities when the lattice is doped with Eu2+ and Dy3+ions [8] Based on the phosphorescence models it is arguedthat electrons are stored in these traps states and then theenergy can be slowly released to produce phosphorescenceby electrons and holes recombination [9] This slow releaseof electrons can allow larger amounts of electrons and holes(e-h+) to be available for the production of hydroxyl radicals(OHminus) which promotes the photocatalysis process [10] Thestudy of the photocatalytic properties of LPPs is importantto find alternative photocatalysts other than TiO

2which has

been recently pointed out as a toxic for aquatic ecosystems[11] Furthermore several studies show that nanosized TiO

2

is toxic for many aquatic species like fish Daphnia magnaand Rainbow fish [12] Bioaccumulation into the gills ofriver fishes has also been reported [13] Hence micrometricsizes of the grains of the photocatalyst are suitable becausethey can be easily removed from water after their use Inaddition there are very few studies about Eu2+Dy3+ dopedstrontiumaluminosilicate powders and their utilization asphotocatalysts Thus the aim of this work is to investigatethe photocatalytic structural morphological and opticalproperties of Eu2+Dy3+ doped-aluminatealuminosilicatephosphors annealed at different temperatures in the range of1000∘Cndash1300∘C

2 Experimental

21 Combustion Synthesis Na2O3Si5H2O (9999)

Sr(NO3)3sdotH2O (999965) Al(NO

3)3sdot9H2O (995)

DyCl3sdot6H2O (999) EuCl

3sdot6H2O (999) NH

4NO3

(999) and H3BO3(95) reagents from Sigma Aldrich

were dissolved in 25mL of deionized water for approximately45 minutes in a quartz beaker on a magnetic stirrer and atransparent solution was formed The AlSr ratio was 76 forall samples and was prepared using 001 moles of Eu2+ 002mole of Dy3+ 15 times 10minus3 mole of NH

4NO3 and 60 times 10minus4

mole of H3BO3 Also 001 mole of urea [CH

4N2O] was added

as fuel and it maximizes the combustion reaction Next thetransparent blend was annealed at 600∘C in atmosphericpressure and the exothermic reaction occurred (combustionprocess) during 10ndash40 seconds As a result (EuDy)-doped strontium aluminatealuminosilicates as-synthesizedpowders were obtained Finally the as-synthesized powderswere put in alumina crucibles and annealed under reductiveatmosphere during 4 h at four different temperatures 1000∘C1150∘C 1200∘C and 1300∘C After this the blue-emittingLPPs of (EuDy)-doped strontium aluminatealuminosilicatepowders were obtained

22 Photocatalysis under UV and Solar Irradiations Forthe photocatalysis experiments the powders were firstground in an agate mortar until we got fine powders The

photocatalytic degradation of the methylene blue (MB) wasmeasured by monitoring the absorbance of MB dissolvedin water at 665 nm The photocatalytic process was carriedout using a reactor fabricated with three 4W UV lampsThose lamps emitted UV light centered at 365 nm witha FWHM around 12 nm The samples for photocatalysiswere prepared by mixing 30mg of (EuDy)-doped strontiumaluminatealuminosilicate powders with a solution 05mMof MB in water This solution was stirred in darkness during1 h in order to adsorb the MB molecules on the surface ofthe powders Afterwards the UV lamps were turned on andsamples of 1mLwere extracted every 30minutes the powderswere separated from the liquid using centrifugation andthen the absorbance spectrum of the liquid was obtained byusing a Cary-60 UV-Vis spectrophotometer in the range of200 nmndash700 nm In the case of solar photocatalysis the sam-ples were exposed under sunlight during a sunny day from1000 am to 400 pm in Saltillo city Mexico The coordinatesin this location were as follows latitude 25∘257061015840 Northlongitude 100∘586161015840 West and height 1581m The averagesolar irradiance was 120575 = 678 plusmn 43Wm2 and it was measuredwith a photodiode 6450 Davis Solar Radiation Sensor

23 Structural and Morphological Characterization The X-ray diffraction (XRD) patterns of the (EuDy)-doped stron-tium aluminatealuminosilicate (1000ndash1300∘C) were per-formed in a Bruker D-8 Advance diffractometer having theBragg-Brentano configuration and CuK

120572radiation (120582 =

15406 A) The XRD patterns were measured in the rangeof 5∘ le 2120579 le 80∘ with 002∘ step size Morphology of thesamples was analyzed using a field emission electron JSM-7800F microscope and 200 kV of accelerating voltage

24 Optical Characterization Excitation spectra photolumi-nescence spectra and phosphorescence decay curves wereobtained by using an Acton Research modular 2300 fluo-rometer The fluorometer was coupled with a pair of SP-500i monochromators (Acton Research) a Xenon lamp(75W) as excitation source of 75W Xenon lamp and aphoto multiplier tube R955 (Hamamatsu) The chromaticitycoordinates and the luminance of the samples were taken byusing a Konica Minolta CS-2000 luminometer For the mea-surements of phosphorescence the (EuDy)-doped strontiumaluminatealuminosilicate powders were irradiated during5 minutes with a 365 nm UV lamp then the excitationwas stopped and the phosphorescent signal as well as theluminance (119871V) was measured The reflectance spectra ofthe powder samples were measured by utilizing Cary-5000spectrophotometer coupled integrating sphere in the rangeof 200 nmndash700 nm All optical measurements were made atroom temperature

3 Results and Discussion

31 Structure and Morphology Figure 1 show the XRD pat-terns of the (EuDy)-doped strontium aluminatealuminosil-icate powders annealed in the range of 1000∘Cndash1300∘C Thesamples annealed at 1150∘C 1200∘C and 1300∘C presented

International Journal of Photoenergy 3

Table 1 Summary of the luminance values energy band- gap estimated values CIE coordinate and morphology of the samples annealed atdifferent temperatures

Sample 119871V (Cdm2) Energy gap (eV) CIE coordinates (119909 119910) Morphology

1000∘C 6 55 (02934 03355) Irregular micrograins1150∘C 27 58 (01708 02209) Bars grains and hexagons1200∘C 40 57 (01589 01972) Bars and hexagons1300∘C 15 58 (01637 02048) Hexagons

120579

120579

120579

lowastlowastlowast

120579lowast

1300∘C

1200∘C

1150∘C

1000∘C

10 20 30 40 50 60 70

2120579 (deg)

Sr3Al32O51SrAl2O4

NaSiAlO4SiO2

120579120579120579120579

120579 120579

120579

120579 120579

120579120579120579

120579120579

120579 120579120579 120579 120579

Figure 1 XRD patterns of the samples as function of temperature

three crystalline phases firstly the SrAl2O4hexagonal phase

(JCPDS 311336) second the Sr3Al32O51

hexagonal phase(JCPDS 440024) and lastly the NaSiAlO

4orthorhombic

phase (JCPDS 390376) The sample annealed at 1000∘C hada fourth phase SiO

2 and it is labeled with the symbol lowast The

SrAl2O4and Sr

3Al32O51standard patterns are plotted at the

bottom of Figure 1 in black and gray vertical lines and theNaSiAlO

4phase is marked with the 120579 symbol on the XRD

patterns in all the samples Furthermore the intensity of thediffraction peaks of the NaSiAlO

4phase is higher for the

samples annealed at 1150∘C and 1200∘C in comparison withthe samples annealed at 1000∘Cand 1300∘CThis suggests thatthe amount of the NaSiAlO

4is lower in the samples annealed

at 1150∘C and 1200∘CThe morphology of the calcined samples is illustrated

in Figures 2(a)ndash2(d) The sample annealed at 1000∘C showsclusters of coalesced grains in the range of 1ndash5 120583m Alsoit can be observed that these irregular grains are porouswhich can be beneficial for the adsorption of MB moleculeson the surface of the powders The samples annealed at1150∘C 1200∘C and 1300∘C also show irregular grains (seeFigures 2(b)ndash2(d)) and the degree of coalescence amonggrains increased as the temperature increases A zoom of thesamples annealed at 1150∘C and 1300∘C samples is shown inFigures 2(e) and 2(f) respectively The sample annealed at1150∘C (see Figure 2(e)) shows a morphology composed ofbars (03ndash08 120583m of average length) hexagons (02ndash05 120583m ofaverage diameter) and irregular grains (01ndash05120583mof average

size) and those ones are coalesced together to form biggermicrograins In addition the sample annealed at 1300∘Cconsisted only in overlapped microhexagons with sizes in therange of 01ndash14 120583m Table 1 summarizes the morphologiesfound for each sample in this work

32 Optical Properties Figure 3 shows the diffuse reflectancespectra of samples with different annealing temperaturesfrom 1000∘C to 1300∘CThe spectra show that the samples arehighly reflective for wavelengths above 456 nm and they havea huge absorption band in the range of 225 nmndash456 nm Thesample annealed at 1000∘C showed the highest absorption oflight in the visible range The reflectance spectra show twomain absorption bands the first one is centered at 270 nmand it is attributed to the absorption of Eu2+ ions [8 9] thesecond absorption band located at 385 nm is attributed to5drarr 4f allowed transition of Eu2+ [14] The band-gap valuesof the samples were estimated by using the Kubelka-Munkfunction methodology [15 16] Figure 4 shows the Kubelka-Munk function for each sample the values of band gap wereobtained by intercepting the extrapolated linear part of thecurves with the 119909-axis of the plot (K-M)12 versus energy(eV) After this the values of band-gaps obtained were inthe range of 55ndash58 eV Those high values suggest that ourmaterial behaves as an insulator

Figure 5(a) depicts the excitation spectra of the samplesannealed at different temperatures that were obtained bymonitoring the emission at 455 nm Those excitation spectraare broad bands centered at 363 nm and they are composedof three peaks at 270 nm 355 nm and 372 nmThe excitationpeaks at 372 nm and 355 nm are related to Eu2+ excitation [917] while the shoulder observed at 270 nm is associated withthe well-known Eu-O charge transfer band [18] Figure 5(b)shows the emission spectra of the samples annealed in therange of 1000∘Cndash1300∘C it shows for all the samples anasymmetrical emission band centered at 120582em = 455 nmwhich is attributed to the 4f65d1 rarr 4f6 (8S

72) allowed

transitions of the Eu2+ [3 9 19 20] This figure also showson the left side images of the samples under UV and wecan appreciate how the phosphorescent intensity increases asthe temperature increases however the intensity decreasedafter we annealed the samples at 1300∘C This decrease ofluminescence as a function of the temperature increase hasbeen observed in SrAl

2O4Eu2+Dy3+ and it is attributed to

higher degree of coalescence of particles which in turndecreases the surface where the photoluminescence processcan occur [21] The asymmetrical band profiles shown inFigure 5(b) are related to the simultaneous presence of the


1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)

100nm

(e)

100nm

(f)

Figure 2 SEM images of samples annealed at (a) 1000∘C (b) 1150∘C (c) 1200∘C and (d) 1300∘C (e) and (f) are a zoomof the samples annealedat 1150∘C and 1300∘C respectively

1300∘C1200∘C

1150∘C1000∘C

200 300 400 500 600 700

Wavelength (nm)

100

80

60

40

20

0

Refle

ctan

ce (

)

270

nm

385

nm

456

nm

Figure 3 Reflectance diffuse spectra of the samples annealed atdifferent temperatures

SrAl2O4and Sr

3Al32O51phases as observed in the XRD pat-

terns In both phases the Eu2+ ions should be substituting theSr2+ ions and therefore we observed a combined emissionof SrAl

2O4Eu2+Sr

3Al32O51Eu2+ which produced a broad

blue-green emission band centered at 455 nm If we have only

1300∘C1200∘C

1150∘C1000∘C

25 30 35 40 45 50 55 60 65

Energy (eV)

55 eV 58 eV

[(K-

M)h

]1

2

Figure 4 Plot of the Kubelka-Munk functions versus energy in eVfor all samples annealed at different temperatures The dashed linesare the tangent lines related to the procedure for the estimation ofthe band-gap energy the intersection of the dashed lines with thehorizontal axis gave us the values of the band-gap energy

SrAl2O4Eu2+ or Sr

3Al32O51Eu2+ we should observe a sharp

emission band of Eu2+ centered at 516 nm (SrAl2O4Eu2+)

or at 450 nm (Sr3Al32O51Eu2+) [3 19 20] but those single


270nm

355nm372nm

Inte

nsity

(au

)

30

25

20

15

10

05

00

times105

200 250 300 350 400 450

Wavelength (nm)

120582em = 455nm

1300∘C1200∘C

1150∘C1000∘C

(a)

1300∘C1200∘C

1150∘C1000∘C

455nm

TiltInte

nsity

(au

)

30

25

20

15

10

05

00

times105

350 400 450 500 550 600

Wavelength (nm)

120582exc = 355nm

(b)

Figure 5 (a) Excitation spectra (120582em = 455 nm) and (b) emission spectra (120582exc = 355 nm) of the samples annealed at different temperatures

1300∘C1200∘C

1150∘C1000∘C

Phos

phor

esce

nce (

au)

100000

10000

1000

100

10

1

Time (min)5 10 15 20 25 30 35 40 45 50 55 60 65

Figure 6 Decay time curves of aluminatealuminosilicate powdersafter excitation with UV light at 365 nm

emissions were not observed in our case Moreover theNaSiAlO

4phase does not contribute to the overall emission

since it did not show yellow-orange emissions in the visibleregion under UV irradiation [22] Further it is worth notingthat no emission of Eu3+ was observed which suggests thatour process of reduction is good enough to dope with onlyEu2+

Figure 6 shows the phosphorescence decay curves of thesamples annealed at different temperatures Those ones weremeasured immediately after we stopped the excitation withUV light at 365 nm (we were exciting the samples during 5minutes) As expected the phosphorescence intensity of thesample annealed at 1200∘C was the highest and it decreasedby three orders of magnitude after 65 minutes while the

rest of samples decreased their intensity by three orders ofmagnitude after only 10 minutes This trend can be related tothe fact that we have bars and hexagons at the same time inthe sample annealed at 1200∘C since the other samples hadgrains or only hexagons and their intensity was lower Thismeans that bars can favor the phosphorescence but irregulargrains can be detrimental for it Furthermore the mixture ofmorphologies can create intrinsic defects which enhances thephosphorescence intensity as reported in literature [23 24]We measured the luminance and CIE coordinates of oursamples and the results are presented in Table 1 the sampleannealed at 1200∘C had the highest luminance (40Cdm2)and its CIE coordinates were (01589 01972) this last coor-dinate indicates that the color of phosphorescence is locatedin the blue-green region Finally the CIE coordinates ofthe rest of samples were similar even though the annealingtemperature increased from 1000∘C to 1300∘C (see Table 1)

33 Photocatalytic Activity of Powders Photocatalysis exper-iments were achieved bymonitoring the percentage degrada-tion of methylene blue (MB) in aqueous solution Typicallythe MB shows an absorbance band (119860) at 665 nm and wemeasured the absorbance intensity of this peak as a functionof time since a decrease of intensity of this band indicatesa decrement of the MB concentration (119862) The followingequation was used in order to calculate the MB degradation() as function of the time [25 26]

Degradation () =1198600minus 119860119905

1198600

times 100 (1)

where 1198600and 119860

119905are the absorbance intensity values of

the dye solution before and after irradiation respectivelyFigure 7(a) shows the percentage degradation of MB as afunction of time The degradation percentages of MB for


1300∘C1200∘C

1150∘C1000∘C

M

B de

grad

atio

n50

40

30

20

10

0

Time (minutes)0 60 120 180 240 300 360

(a)

MB

degr

adat

ion

40

60

80

100

20

0

1300∘C1200∘C

1150∘C1000∘C

Time (minutes)0 50 100 150 200 250 300

(b)

Figure 7 Degradation curves of MB (a) under UV light at 365 nm and (b) under solar irradiation

the samples annealed at 1000∘C 1150∘C 1200∘C and 1300∘Cafter 360min of UV excitation were 32 20 15 and385 respectively Thus the samples annealed at 1000∘Cand 1300∘Cpresented the highest percentage degradation andthe lowest luminescent intensities In contrast the sampleswith the highest luminescent intensity (1150∘C and 1200∘C)exhibited the lowest photocatalytic activity The decreasein the photocatalytic activity has been observed in otherluminescent systems [25 27] and this is due to the factthat the samples with lower luminescence generate morefree-carriers (electron or holes) during the phosphorescenceprocess comparedwith the sampleswith higher luminescencewhich use most of the electronhole pairs to generate lightemission In consequence as the availability of free-carriersis better the photocatalytic activity is enhanced [28 29]Figure 7(b) shows the percentage degradation of the samplesexposed to solar irradiation as a function of time It isobserved that the samples annealed at 1000∘C 1150∘C and1200∘C degraded 100 the MB dye after 300min this meansan increase of 68 80 and 85 of the MB degradationcompared with the results obtained under UV light Thesample calcined at 1300∘C degrades only sim88 of methyleneblue in water solution after 360min (see Figure 7(b)) Thislower degradation percentage is related to the fact that higherannealing temperature promotes the coalescence of grainswhich in turn reduces the surface area and this reducesthe amount of methylene blue molecules adsorbed on thepowders This can be corroborated from SEM images sincewe find bigger pieces of coalesced material in the samplesannealed at 1300∘C in comparison with the rest of samples(see Figures 2(a)ndash2(d))

Based on the results mentioned above we consider thatour phosphors have modest photocatalysis activity (underUV light) compared to conventional TiO

2nanoparticles [26

28] However an advantage of our (EuDy)-doped strontiumaluminatesaluminosilicates as photocatalyst is the fact thatthey can be separated easily from water by using simpleprecipitation which is more difficult for conventional TiO

2

nanoparticles The best performance of our phosphors ispresented under solar irradiation this suggests that they canbe used as photocatalysts in water treatment plans We arecurrentlyworking to obtain only one single phase that is onlystrontium aluminate or aluminosilicates in order to obtainthe photocatalytic performance of each phase separatelyThose results will be published in a subsequent article

4 Conclusions

Strontium aluminatealuminosilicate phosphorescent phos-phors based on the mixture of SrAl

2O4Eu2+Dy3+

Sr3Al32O51Eu2+Dy3+ and NaSiAlO

4were successfully

fabricated by combustion synthesis and postannealedThe blue-green phosphorescence emission at 455 nmis ascribed to the 4f-5d allowed transition of the Eu2+The sample with the longest phosphorescence was thatannealed at 1200∘C and it had a luminance of 40Cdm2 Thephotocatalyst experiments with our samples demonstratedthat these samples annealed at 1000∘C and 1300∘C showedthe lowest luminescence intensity but the highest percentagedegradation of MB under UV excitation at 365 nm (32and 385 resp) When solar irradiation was used forthe photocatalysis experiments total degradation ofMB was observed by using the samples annealed at1000∘C 1150∘C and 1200∘C after 300 minutes Also thosepowders were separated easily from water by simpleprecipitation Hence the results suggest that our strontiumaluminatealuminosilicate phosphorescent blue phosphorpowders can be useful for water cleaning systems


Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors appreciate the excellent technical work per-formed by R Valdivia C Albor and M Olmos C R Garcıathanks CONACYT-Mexico for national postdoctoral fellow-ship PRODEP-SEP 2015 project and FONCYT-COECYT2016 project One of the author thanks Drs R Narro CMendez and K Linganna for their helpful comments anddiscussions

References

[1] K van den Eeckhout D Poelman and P F Smet ldquoPersistentluminescence in non-Eu2+-doped compounds a reviewrdquoMate-rials vol 6 no 7 pp 2789ndash2818 2013

[2] T Matsuzawa Y Aoki N Takeuchi and Y Murayama ldquoAnew long phosphorescent phosphor with high brightnessSrAl2O4Eu2+ Dy3+rdquo Journal of the Electrochemical Society vol

143 no 8 pp 2670ndash2673 1996[3] N M Son L T T Vien L V K Bao and N N Trac ldquoSynthesis

of SrAl2O4 Eu2+ Dy3+ phosphorescence nanosized powder

by combustion method and its optical propertiesrdquo Journal ofPhysics Conference Series vol 187 article 012017 2009

[4] K Van den Eeckhout P F Smet and D Poelman ldquoPersistentluminescence in Eu2+-doped compounds a reviewrdquo Materialsvol 3 no 4 pp 2536ndash2566 2010

[5] J B Zhong D Ma X Y He J Z Li and Y Q Chen ldquoSol-gelpreparation and photocatalytic performance of TiO

2SrAl2O4

Eu2+ Dy3+ toward the oxidation of gaseous benzenerdquo Journal ofSol-Gel Science and Technology vol 52 no 1 pp 140ndash145 2009

[6] H Li S Yin Y Wang and T Sato ldquoPersistent lumines-cence assisted photocatalytic properties of CaAl

2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO

2minus119909N119910rdquo Journal of Mo-

lecular Catalysis A Chemical vol 363-364 pp 129ndash133 2012[7] H Li S Yin Y Wang T Sekino S W Lee and T Sato ldquoGreen

phosphorescence-assisted degradation of rhodamine B dyes byAg3PO4rdquo Journal ofMaterials ChemistryA vol 1 no 4 pp 1123ndash

1126 2013[8] T Peng L Huajun H Yang and C Yan ldquoSynthesis of

SrAl2O4Eu Dy phosphor nanometer powders by sol-gel pro-

cesses and its optical propertiesrdquo Materials Chemistry andPhysics vol 85 no 1 pp 68ndash72 2004

[9] F Clabau X Rocquefelte S Jobic et al ldquoMechanism ofphosphorescence appropriate for the long-lasting phosphorsEu2+-doped SrAl

2O4with codopants Dy3+ and B3+rdquo Chemistry

of Materials vol 17 no 15 pp 3904ndash3912 2005[10] A L Linsebigler G Lu and J T Yates Jr ldquoPhotocatalysis on

TiO2surfaces principles mechanisms and selected resultsrdquo

Chemical Reviews vol 95 no 3 pp 735ndash758 1995[11] G Federici B J Shaw and R D Handy ldquoToxicity of titanium

dioxide nanoparticles to rainbow trout (Oncorhynchus mykiss)gill injury oxidative stress and other physiological effectsrdquoAquatic Toxicology vol 84 no 4 pp 415ndash430 2007

[12] X Zhu Y Chang and Y Chen ldquoToxicity and bioaccumulationof TiO

2nanoparticle aggregates in Daphnia magnardquo Chemo-

sphere vol 78 no 3 pp 209ndash215 2010

[13] W-W Yang Y Wang B Huang et al ldquoTiO2nanoparticles act

as a carrier of Cd bioaccumulation in the ciliate Tetrahymenathermophilardquo Environmental Science amp Technology vol 48 no13 pp 7568ndash7575 2014

[14] T W Kim and H L Park ldquoObservation of two valence states ofEu in a SrS

119909O1minus119909

Eu119910phosphorrdquo Solid State Communications

vol 85 no 7 pp 635ndash637 1993[15] J Tauc ldquoOptical properties and electronic structure of amor-

phous Ge and Sirdquo Materials Research Bulletin vol 3 no 1 pp37ndash46 1968

[16] A Escobedo Morales E Sanchez Mora and U Pal ldquoUse ofdiffuse reflectance spectroscopy for optical characterization ofun-supported nanostructuresrdquo Revista Mexicana de Fısica vol53 pp 18ndash22 2007

[17] X Luo W Cao and F Sun ldquoThe development of silicate matrixphosphors with broad excitation band for phosphor-converedwhite LEDrdquo Chinese Science Bulletin vol 53 no 19 pp 2923ndash2930 2008

[18] G Blasse and B C Grabmaier Luminescent Materials vol 2Springer Berlin Germany 1994

[19] Y-F Xu D-K Ma M-L Guan X-A Chen Q-Q Panand S-M Huang ldquoControlled synthesis of single-crystalSrAl2O4Eu2+Dy3+ nanosheets with long-lasting phosphores-

cencerdquo Journal of Alloys and Compounds vol 502 no 1 pp 38ndash42 2010

[20] M A Kale C P Joshi and S VMoharil ldquoPreparation and pho-toluminescence study of Eu2+ doped SrAl

4O7and Sr

3Al32O51rdquo

International Journal of Chemical and Physical Sciences vol 1no 2 pp 35ndash39 2012

[21] M Gaft W Strek L Nagli G Panczer G R Rossman andL Marciniak ldquoLaser-induced time-resolved luminescence ofnatural sillimanite Al

2SiO5and synthetic Al

2SiO5activated by

chromiumrdquo Journal of Luminescence vol 132 no 11 pp 2855ndash2862 2012

[22] S Deng Z Xue Q Yang et al ldquoSurface modification ofMAl2O4Eu2+Dy3+ (M = Sr Ca Ba) phosphors to enhance

water resistance by combustion methodrdquo Applied Surface Sci-ence vol 282 pp 315ndash319 2013

[23] T LaamanenDefects in persistent luminescencematerials [PhDthesis] Universidad of Turku Graduate School of MaterialsResearch Turku Finland 2011 S Ser and A I Osa

[24] H Ryu and K S Bartwal ldquoDefect structure and its relevanceto photoluminescence in SrAl

2O4Eu2+ Nd3+rdquo Physica B Con-

densed Matter vol 404 no 12-13 pp 1714ndash1718 2009[25] R Borja-Urby L A Dıaz-Torres P Salas E Moctezuma M

Vega and C Angeles-Chavez ldquoStructural study photolumines-cence and photocatalytic activity of semiconducting BaZrO

3Bi

nanocrystalsrdquoMaterials Science and Engineering B vol 176 no17 pp 1382ndash1387 2011

[26] A Houas H Lachheb M Ksibi E Elaloui C Guillardand J-M Herrmann ldquoPhotocatalytic degradation pathway ofmethylene blue in waterrdquo Applied Catalysis B Environmentalvol 31 no 2 pp 145ndash157 2001

[27] D Wojcieszak D Kaczmarek J Domaradzki and M MazurldquoCorrelation of photocatalysis and photoluminescence effectin relation to the surface properties of TiO

2Tb thin filmsrdquo

International Journal of Photoenergy vol 2013 Article ID526140 9 pages 2013

[28] S-Y Kim T-H Lim T-S Chang and C-H Shin ldquoPhoto-catalysis of methylene blue on titanium dioxide nanoparticlessynthesized by modified sol-hydrothermal process of TiCl

4rdquo

Catalysis Letters vol 117 no 3-4 pp 112ndash118 2007


[29] C R Garcıa L A Diaz-Torres P Salas M Guzman and CAngeles-Chavez ldquoPhotoluminescent and photocatalytic prop-erties of bismuth doped strontiumaluminates blendedwith tita-nium dioxiderdquo Materials Science in Semiconductor Processingvol 37 pp 105ndash111 2015

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


The utilization of LPPs for photocatalytic applications hasbeen attractive because the phosphorescent materials haveelectrons with high mobility from the valence band (VB)levels to the traps levels which can act as electrons storageand this fact can favor the photocatalytic properties [8]Thesetraps levels are usually generated by oxygen vacancy defectsor impurities when the lattice is doped with Eu2+ and Dy3+ions [8] Based on the phosphorescence models it is arguedthat electrons are stored in these traps states and then theenergy can be slowly released to produce phosphorescenceby electrons and holes recombination [9] This slow releaseof electrons can allow larger amounts of electrons and holes(e-h+) to be available for the production of hydroxyl radicals(OHminus) which promotes the photocatalysis process [10] Thestudy of the photocatalytic properties of LPPs is importantto find alternative photocatalysts other than TiO

2which has

been recently pointed out as a toxic for aquatic ecosystems[11] Furthermore several studies show that nanosized TiO

2

is toxic for many aquatic species like fish Daphnia magnaand Rainbow fish [12] Bioaccumulation into the gills ofriver fishes has also been reported [13] Hence micrometricsizes of the grains of the photocatalyst are suitable becausethey can be easily removed from water after their use Inaddition there are very few studies about Eu2+Dy3+ dopedstrontiumaluminosilicate powders and their utilization asphotocatalysts Thus the aim of this work is to investigatethe photocatalytic structural morphological and opticalproperties of Eu2+Dy3+ doped-aluminatealuminosilicatephosphors annealed at different temperatures in the range of1000∘Cndash1300∘C

2 Experimental

21 Combustion Synthesis Na2O3Si5H2O (9999)

Sr(NO3)3sdotH2O (999965) Al(NO

3)3sdot9H2O (995)

DyCl3sdot6H2O (999) EuCl

3sdot6H2O (999) NH

4NO3

(999) and H3BO3(95) reagents from Sigma Aldrich

were dissolved in 25mL of deionized water for approximately45 minutes in a quartz beaker on a magnetic stirrer and atransparent solution was formed The AlSr ratio was 76 forall samples and was prepared using 001 moles of Eu2+ 002mole of Dy3+ 15 times 10minus3 mole of NH

4NO3 and 60 times 10minus4

mole of H3BO3 Also 001 mole of urea [CH

4N2O] was added

as fuel and it maximizes the combustion reaction Next thetransparent blend was annealed at 600∘C in atmosphericpressure and the exothermic reaction occurred (combustionprocess) during 10ndash40 seconds As a result (EuDy)-doped strontium aluminatealuminosilicates as-synthesizedpowders were obtained Finally the as-synthesized powderswere put in alumina crucibles and annealed under reductiveatmosphere during 4 h at four different temperatures 1000∘C1150∘C 1200∘C and 1300∘C After this the blue-emittingLPPs of (EuDy)-doped strontium aluminatealuminosilicatepowders were obtained

22 Photocatalysis under UV and Solar Irradiations Forthe photocatalysis experiments the powders were firstground in an agate mortar until we got fine powders The

photocatalytic degradation of the methylene blue (MB) wasmeasured by monitoring the absorbance of MB dissolvedin water at 665 nm The photocatalytic process was carriedout using a reactor fabricated with three 4W UV lampsThose lamps emitted UV light centered at 365 nm witha FWHM around 12 nm The samples for photocatalysiswere prepared by mixing 30mg of (EuDy)-doped strontiumaluminatealuminosilicate powders with a solution 05mMof MB in water This solution was stirred in darkness during1 h in order to adsorb the MB molecules on the surface ofthe powders Afterwards the UV lamps were turned on andsamples of 1mLwere extracted every 30minutes the powderswere separated from the liquid using centrifugation andthen the absorbance spectrum of the liquid was obtained byusing a Cary-60 UV-Vis spectrophotometer in the range of200 nmndash700 nm In the case of solar photocatalysis the sam-ples were exposed under sunlight during a sunny day from1000 am to 400 pm in Saltillo city Mexico The coordinatesin this location were as follows latitude 25∘257061015840 Northlongitude 100∘586161015840 West and height 1581m The averagesolar irradiance was 120575 = 678 plusmn 43Wm2 and it was measuredwith a photodiode 6450 Davis Solar Radiation Sensor

23 Structural and Morphological Characterization The X-ray diffraction (XRD) patterns of the (EuDy)-doped stron-tium aluminatealuminosilicate (1000ndash1300∘C) were per-formed in a Bruker D-8 Advance diffractometer having theBragg-Brentano configuration and CuK

120572radiation (120582 =

15406 A) The XRD patterns were measured in the rangeof 5∘ le 2120579 le 80∘ with 002∘ step size Morphology of thesamples was analyzed using a field emission electron JSM-7800F microscope and 200 kV of accelerating voltage

24 Optical Characterization Excitation spectra photolumi-nescence spectra and phosphorescence decay curves wereobtained by using an Acton Research modular 2300 fluo-rometer The fluorometer was coupled with a pair of SP-500i monochromators (Acton Research) a Xenon lamp(75W) as excitation source of 75W Xenon lamp and aphoto multiplier tube R955 (Hamamatsu) The chromaticitycoordinates and the luminance of the samples were taken byusing a Konica Minolta CS-2000 luminometer For the mea-surements of phosphorescence the (EuDy)-doped strontiumaluminatealuminosilicate powders were irradiated during5 minutes with a 365 nm UV lamp then the excitationwas stopped and the phosphorescent signal as well as theluminance (119871V) was measured The reflectance spectra ofthe powder samples were measured by utilizing Cary-5000spectrophotometer coupled integrating sphere in the rangeof 200 nmndash700 nm All optical measurements were made atroom temperature

3 Results and Discussion

31 Structure and Morphology Figure 1 show the XRD pat-terns of the (EuDy)-doped strontium aluminatealuminosil-icate powders annealed in the range of 1000∘Cndash1300∘C Thesamples annealed at 1150∘C 1200∘C and 1300∘C presented





120579

120579

120579

lowastlowastlowast

120579lowast

1300∘C

1200∘C

1150∘C

1000∘C

10 20 30 40 50 60 70

2120579 (deg)

Sr3Al32O51SrAl2O4

NaSiAlO4SiO2

120579120579120579120579

120579 120579

120579

120579 120579

120579120579120579

120579120579

120579 120579120579 120579 120579





4orthorhombic



SrAl2O4and Sr













72) allowed





1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)

100nm

(e)

100nm

(f)


1300∘C1200∘C

1150∘C1000∘C

200 300 400 500 600 700

Wavelength (nm)

100

80

60

40

20

0

Refle

ctan

ce (

)

270

nm

385

nm

456

nm


SrAl2O4and Sr



2O4Eu2+Sr



1300∘C1200∘C

1150∘C1000∘C

25 30 35 40 45 50 55 60 65

Energy (eV)

55 eV 58 eV

[(K-

M)h

]1

2


SrAl2O4Eu2+ or Sr





270nm

355nm372nm

Inte

nsity

(au

)

30

25

20

15

10

05

00

times105

200 250 300 350 400 450

Wavelength (nm)

120582em = 455nm

1300∘C1200∘C

1150∘C1000∘C

(a)

1300∘C1200∘C

1150∘C1000∘C

455nm

TiltInte

nsity

(au

)

30

25

20

15

10

05

00

times105

350 400 450 500 550 600

Wavelength (nm)

120582exc = 355nm

(b)


1300∘C1200∘C

1150∘C1000∘C

Phos

phor

esce

nce (

au)

100000

10000

1000

100

10

1

Time (min)5 10 15 20 25 30 35 40 45 50 55 60 65









1198600

times 100 (1)

where 1198600and 119860




1300∘C1200∘C

1150∘C1000∘C

M

B de

grad

atio

n50

40

30

20

10

0

Time (minutes)0 60 120 180 240 300 360

(a)

MB

degr

adat

ion

40

60

80

100

20

0

1300∘C1200∘C

1150∘C1000∘C

Time (minutes)0 50 100 150 200 250 300

(b)




2nanoparticles [26


2


4 Conclusions


2O4Eu2+Dy3+


4were successfully



Competing Interests


Acknowledgments


References








2SrAl2O4



2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO



















119909O1minus119909










4O7and Sr

3Al32O51rdquo




2SiO5activated by









3Bi




2Tb thin filmsrdquo



4rdquo













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





120579

120579

120579

lowastlowastlowast

120579lowast

1300∘C

1200∘C

1150∘C

1000∘C

10 20 30 40 50 60 70

2120579 (deg)

Sr3Al32O51SrAl2O4

NaSiAlO4SiO2

120579120579120579120579

120579 120579

120579

120579 120579

120579120579120579

120579120579

120579 120579120579 120579 120579





4orthorhombic



SrAl2O4and Sr













72) allowed





1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)

100nm

(e)

100nm

(f)


1300∘C1200∘C

1150∘C1000∘C

200 300 400 500 600 700

Wavelength (nm)

100

80

60

40

20

0

Refle

ctan

ce (

)

270

nm

385

nm

456

nm


SrAl2O4and Sr



2O4Eu2+Sr



1300∘C1200∘C

1150∘C1000∘C

25 30 35 40 45 50 55 60 65

Energy (eV)

55 eV 58 eV

[(K-

M)h

]1

2


SrAl2O4Eu2+ or Sr





270nm

355nm372nm

Inte

nsity

(au

)

30

25

20

15

10

05

00

times105

200 250 300 350 400 450

Wavelength (nm)

120582em = 455nm

1300∘C1200∘C

1150∘C1000∘C

(a)

1300∘C1200∘C

1150∘C1000∘C

455nm

TiltInte

nsity

(au

)

30

25

20

15

10

05

00

times105

350 400 450 500 550 600

Wavelength (nm)

120582exc = 355nm

(b)


1300∘C1200∘C

1150∘C1000∘C

Phos

phor

esce

nce (

au)

100000

10000

1000

100

10

1

Time (min)5 10 15 20 25 30 35 40 45 50 55 60 65









1198600

times 100 (1)

where 1198600and 119860




1300∘C1200∘C

1150∘C1000∘C

M

B de

grad

atio

n50

40

30

20

10

0

Time (minutes)0 60 120 180 240 300 360

(a)

MB

degr

adat

ion

40

60

80

100

20

0

1300∘C1200∘C

1150∘C1000∘C

Time (minutes)0 50 100 150 200 250 300

(b)




2nanoparticles [26


2


4 Conclusions


2O4Eu2+Dy3+


4were successfully



Competing Interests


Acknowledgments


References








2SrAl2O4



2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO



















119909O1minus119909










4O7and Sr

3Al32O51rdquo




2SiO5activated by









3Bi




2Tb thin filmsrdquo



4rdquo













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)

100nm

(e)

100nm

(f)


1300∘C1200∘C

1150∘C1000∘C

200 300 400 500 600 700

Wavelength (nm)

100

80

60

40

20

0

Refle

ctan

ce (

)

270

nm

385

nm

456

nm


SrAl2O4and Sr



2O4Eu2+Sr



1300∘C1200∘C

1150∘C1000∘C

25 30 35 40 45 50 55 60 65

Energy (eV)

55 eV 58 eV

[(K-

M)h

]1

2


SrAl2O4Eu2+ or Sr





270nm

355nm372nm

Inte

nsity

(au

)

30

25

20

15

10

05

00

times105

200 250 300 350 400 450

Wavelength (nm)

120582em = 455nm

1300∘C1200∘C

1150∘C1000∘C

(a)

1300∘C1200∘C

1150∘C1000∘C

455nm

TiltInte

nsity

(au

)

30

25

20

15

10

05

00

times105

350 400 450 500 550 600

Wavelength (nm)

120582exc = 355nm

(b)


1300∘C1200∘C

1150∘C1000∘C

Phos

phor

esce

nce (

au)

100000

10000

1000

100

10

1

Time (min)5 10 15 20 25 30 35 40 45 50 55 60 65









1198600

times 100 (1)

where 1198600and 119860




1300∘C1200∘C

1150∘C1000∘C

M

B de

grad

atio

n50

40

30

20

10

0

Time (minutes)0 60 120 180 240 300 360

(a)

MB

degr

adat

ion

40

60

80

100

20

0

1300∘C1200∘C

1150∘C1000∘C

Time (minutes)0 50 100 150 200 250 300

(b)




2nanoparticles [26


2


4 Conclusions


2O4Eu2+Dy3+


4were successfully



Competing Interests


Acknowledgments


References








2SrAl2O4



2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO



















119909O1minus119909










4O7and Sr

3Al32O51rdquo




2SiO5activated by









3Bi




2Tb thin filmsrdquo



4rdquo













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


270nm

355nm372nm

Inte

nsity

(au

)

30

25

20

15

10

05

00

times105

200 250 300 350 400 450

Wavelength (nm)

120582em = 455nm

1300∘C1200∘C

1150∘C1000∘C

(a)

1300∘C1200∘C

1150∘C1000∘C

455nm

TiltInte

nsity

(au

)

30

25

20

15

10

05

00

times105

350 400 450 500 550 600

Wavelength (nm)

120582exc = 355nm

(b)


1300∘C1200∘C

1150∘C1000∘C

Phos

phor

esce

nce (

au)

100000

10000

1000

100

10

1

Time (min)5 10 15 20 25 30 35 40 45 50 55 60 65









1198600

times 100 (1)

where 1198600and 119860




1300∘C1200∘C

1150∘C1000∘C

M

B de

grad

atio

n50

40

30

20

10

0

Time (minutes)0 60 120 180 240 300 360

(a)

MB

degr

adat

ion

40

60

80

100

20

0

1300∘C1200∘C

1150∘C1000∘C

Time (minutes)0 50 100 150 200 250 300

(b)




2nanoparticles [26


2


4 Conclusions


2O4Eu2+Dy3+


4were successfully



Competing Interests


Acknowledgments


References








2SrAl2O4



2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO



















119909O1minus119909










4O7and Sr

3Al32O51rdquo




2SiO5activated by









3Bi




2Tb thin filmsrdquo



4rdquo













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


1300∘C1200∘C

1150∘C1000∘C

M

B de

grad

atio

n50

40

30

20

10

0

Time (minutes)0 60 120 180 240 300 360

(a)

MB

degr

adat

ion

40

60

80

100

20

0

1300∘C1200∘C

1150∘C1000∘C

Time (minutes)0 50 100 150 200 250 300

(b)




2nanoparticles [26


2


4 Conclusions


2O4Eu2+Dy3+


4were successfully



Competing Interests


Acknowledgments


References








2SrAl2O4



2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO



















119909O1minus119909










4O7and Sr

3Al32O51rdquo




2SiO5activated by









3Bi




2Tb thin filmsrdquo



4rdquo













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Competing Interests


Acknowledgments


References








2SrAl2O4



2O4(EuNd)

TiO2minus119909

N119910and Sr

4Al14O25(EuDy)TiO



















119909O1minus119909










4O7and Sr

3Al32O51rdquo




2SiO5activated by









3Bi




2Tb thin filmsrdquo



4rdquo













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of












Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article photocatalytic activity and optical...

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