Journal of Luminescence 145 (2014) 202–207

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Journal of Luminescence

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Investigation of energy transfer between PM567:Rh610 dye mixturein modified poly (methyl methacrylate)

Xiaohui Li a,b, Rongwei Fan a,b, Xin Yu a,b, Deying Chen a,b,n

a National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin 150080, Chinab Institute of Opto-electronics, Harbin Institute of Technology, Harbin 150080, China

a r t i c l e i n f o

Article history:Received 24 February 2013Received in revised form29 May 2013Accepted 10 July 2013Available online 19 July 2013

Keywords:Energy transferDye mixtureSolid dyeMPMMAStern–Volmer plot

13/$ - see front matter & 2013 Published by Ex.doi.org/10.1016/j.jlumin.2013.07.039

esponding author at: National Key LaboratoryLaser, Science Park of Harbin Institute of T

ng Str., Harbin 150080, China. Tel.: +86 451 86451 86413161.ail addresses: lixiaohuihit@163.com (X. Li), dy

a b s t r a c t

In this paper, solid dye samples were prepared by codoping laser dyes Pyrromethene 567 (PM567) as theenergy donor and Rhodamine 610 (Rh610) as the energy acceptor into the ethanol modified poly (methylmethacrylate) matrix (MPMMA) to enhance the properties of the solid dye lasers. The fluorescenceintensity of the acceptor was enhanced by up to 9 fold with the introduction of the donor molecules. Thelaser efficiency of the dye mixture doped samples was improved by up to 8 times relative to that of thesamples solely doped with the acceptor, and the highest slope efficiency was obtained as 70.4%. Theradiative and nonradiative energy transfer rate constants (KR and KNR) were calculated using the Stern–Volmer plots and the acceptor concentration dependence of the radiative and nonradiative transferefficiencies were also obtained. The KR was three orders of magnitude higher than the KNR, indicating thedominance of the radiative energy transfer mechanism in the present system. The deviation of the Stern–Volmer plot from the linearity demonstrated that both the dynamic and transient quenching mechanismexist in the present energy transfer system.

& 2013 Published by Elsevier B.V.

1. Introduction

Solid state dye lasers have attracted the attention of manyresearchers in recent years [1–12], due to its benefits comparedwith conventional liquid dye lasers, such as compactness, low cost,and easiness of handling. Many research efforts have been devotedto the development of high quality solid matrices with high laserefficiency and good photostability. However, for some laser dyes,the laser efficiency is still too low when directly pumped by themature commercial lasers, especially for those dyes lasing in thered to near infrared region of the spectrum. Many researchesindicate that by codoping dye mixtures into the liquid solutions[13–17] or solid matrices[18–23], with one dye serving as theenergy donor and another dye as the energy acceptor, the laserefficiency of the acceptor can be greatly enhanced due to theenergy transfer process.

Several dye energy transfer systems have been reported in thesolid state matrices. By doping dye mixture Rh6G:RhB into poly(methyl methacrylate) (PMMA) matrix, Kumar et al. [20] demon-strated an enhancement of the fluorescence intensity of RhB by226%. Clendinen et al. [21] investigated the energy transfer of

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of Science and Technology onechnology, Rm.217, Bld. 2A,402837;

chen@hit.edu.cn (D. Chen).

Perylene Red (P-red) with DTTC and HITC acceptor dyes in PMMAfilms. They reported a 100-fold enhancement of the near-IRfluorescence by the introduction of the donor dye. Nhung et al.[18] investigated the energy transfer between RhB and P-red inxerogel matrices and obtained wide tuning band control andincreased efficiency with respect to the samples using the acceptoronly. Yang et al. [22] obtained enhanced laser performances basedon energy transfer with several coumarin dyes and PM567 as thedonors and P-red as the acceptor. They obtained a two-foldenhancement in laser efficiency and a tunable range of 80 nm.

The mechanisms for the energy transfer in the dye mixturesinclude [15,24–27] radiative energy transfer and nonradiativeenergy transfer. The radiative transfer is realized with the absorp-tion of the emission of the donor by the acceptor. The nonradiativeenergy transfer depends on the interaction between the donor andthe acceptor molecules during the excitation lifetime of the donor.This mechanism can be divided into two types, (a) diffusion-controlled energy transfer, which occurs over intermoleculardistances of the order of molecular distances; (b) resonanceenergy transfer due to long-range dipole–dipole interaction andthe process occurs with the donor–acceptor separation muchgreater than the collisional diameters. The dominant mechanismsof the energy transfer can be determined by measuring theradiative and nonradiative energy transfer rate constants withthe Stern–Volmer plots [15,24,25].

In this paper, Pyrromethene 567 (PM567) as the energy donor,and Rhodamine 610 (Rh610) as the energy acceptor were codoped

1500

2000

2500

3000

3500

4000

4500

σ A (1

08 cm2 /m

ol)

scen

ce In

tens

ity (a

.u.)

Fluorescence PM567

1.0

1.5

2.0

2.5

3.0Absorption

Rh610

X. Li et al. / Journal of Luminescence 145 (2014) 202–207 203

into the ethanol modified PMMA (MPMMA) matrices to enhancethe laser properties of the solid dye lasers. The fluorescence andlaser properties of the solid dye samples were investigated withthe 532 nm output of a Q-switched Nd:YAG laser as the pumpingsource. The radiative rate constant (KR) and nonradiative rateconstant (KNR) were obtained using the Stern–Volmer plots, andthe acceptor concentration dependence of radiative and nonradia-tive transfer efficiencies were also obtained to determine thedominant energy transfer mechanism in the present system.

450 500 550 600 650 7000

500

1000

Fluo

re

Wavelength (nm)

0.0

0.5

Fig. 1. The overlap between the emission spectrum of the donor of 1�10�4 M andthe absorption spectrum of the acceptor of 0.5�10�4 M in ethanol.

500 550 600 650 7000

2500

5000

7500

10000

12500

Fluo

resc

ence

inte

nsity

(a.u

.)

Wavelength (nm)

concentration ratioPM567:Rh610=2:0.5

PM567:Rh610=2:2 PM567:Rh610=2:5 PM567:Rh610=2:8 PM567:Rh610=2:15 PM567:Rh610=2:0

Fig. 2. The fluorescence spectra of PM567:Rh610 dye mixture doped MPMMAsamples with fixed donor concentration at 2�10�4 M and varying acceptorconcentrations.

2. Experimental

PM567 and Rh610 (Exciton Inc.) were used as received withoutfurther purification. The methyl methacrylate (MMA) was purifiedusing the method described in Ref [28]. The dye mixtures withadequate molecular concentration ratios were firstly solved inpure ethanol (spectroscopic grade, 499.9%) and then mixed withthe purified MMA with the volume ratio of ethanol:MMA fixed to1:10. Thermal initiator α,α-azoisobutyronitrile (AIBN) was added tothe mixture and then the mixture was sonicated. The resulted dyesolution was filtered into cylindrical mounds and sealed. Thepolymerization was performed in the dark in a thermostatic baseat 40 1C until solidification. The MPMMA samples were cut intocylindrical disks (2 mm in thickness) and rods (25 mm in length).The disk samples were prepared for the fluorescence measure-ments and the rod samples were prepared for the laser propertyinvestigation. The samples were machine polished for themeasurements.

The absorption spectra of the dye molecules were measuredusing a Shimadzu UV-3010PC spectrophotometer. The fluorescespectra were obtained by pumping the disk samples with thesecond harmonic generation (SHG, 532 nm, ∼13 ns) of a home-made Q-switched Nd:YAG laser and detecting the fluorescence atthe right angle with a high resolution (∼0.25 nm) portablespectrometer (HR4000, Ocean Optics). The laser properties suchas the laser spectra and slope efficiencies were obtained in alongitudinally pumped solid state dye laser system [12]. Thepumping source was the SHG of the home-made Q-switched Nd:YAG laser. The dye laser cavity was 10 cm, and consisted of adichroic mirror with high transmittance at 532 nm and highreflectance from 550 nm to 650 nm, and an output mirror with70% transmission from 550 nm to 590 nm. The fluorescence life-time of the donors with the absence of the acceptor was measuredusing the 530 nm, ∼50 fs output of a femtosecond optical para-meter amplifier (OPA, TOPAS, Coherent) as the pumping source. Acombination of fast silicon PIN detector (DET210, Thorlabs) and a1 GHz digital storage oscilloscope (DPO7104, Tektronix) was usedas the detection system.

3. Results and discussion

3.1. Fluorescence spectra analysis

The effective energy transfer between the donor and theacceptor depends greatly on the overlap between the emissionspectrum of the donor and the absorption spectrum of theacceptor. Shown in Fig. 1 is the overlap between the fluorescencespectrum of the donor of 1�10�4 mol/L (M) and the absorptionspectrum of acceptor of 0.5�10�4 M in ethanol solution. The largearea of overlap indicates that the energy transfer between thedonor and the acceptor should be possible [18,20,23].

The fluorescence spectra of MPMMA solid dye samples withfixed donor concentration as 2�10�4 M and varying acceptorconcentrations are shown in Fig. 2. There are two peaks in the

fluorescence spectra when the acceptor concentration is lowerthan 8�10�4 M, one around the donor peak emission wavelength,and one around the acceptor peak emission wavelength. This isconsistent with the results of Sesha Bamini et al. [23], who alsoreported two emission peaks in the fluorescence spectra of theC480:C535 dye mixture doped MPMMA matrices. With theincrease of the acceptor concentration, the intensity of the donoremission peak decreases gradually while the intensity of theacceptor emission peak increases gradually. This is a clear indicationof the effective energy transfer between the donor and the acceptor.When the acceptor concentration approaches 15�10�4 M, thedonor emission peak is totally absorbed by the acceptor. The intensityof the acceptor peak with acceptor concentration of 15�10�4 Mdecreases a bit relative to that corresponding to 8�10�4 M. Thedecrease is perhaps due to the concentration quenching effect or dueto the formation of nonradiative dimers[29]. The wavelength of theacceptor peak is red-shifted, which is due to the self-absorption andre-emission effect [30].

Shown in Fig. 3 are the fluorescence spectra of the MPMMAsolid dye samples with fixed acceptor concentration at 2�10�4 Mand varying donor concentrations. It is shown that with theincrease of the donor concentration, the intensity of the acceptorpeak increases gradually. The largest enhancement is obtained as9 fold with the donor:acceptor concentration ratio of 10:2. Itindicates that the energy transfer between the donor and theacceptor is an effective method to improve the fluorescence

500 550 600 650 7000

2000

4000

6000

8000

10000

12000

14000

16000

Fluo

resc

ence

inte

nsity

(a.u

.)

Wavelength (nm)

concentration ratio PM567:Rh610=1:0 PM567:Rh610=1:2 PM567:Rh610=2:2 PM567:Rh610=5:2 PM567:Rh610=10:2 PM567:Rh610=15:2 PM567:Rh610=0:2

Fig. 3. The fluorescence spectra of PM567:Rh610 dye mixture doped MPMMAsamples with fixed acceptor concentration at 2�10�4 M and varying donorconcentrations.

540 560 580 600 620 640 6600.0

0.2

0.4

0.6

0.8

1.0

Inte

nsity

(a.u

.)

Wavelength(nm)

concentration ratioPM567:Rh610=2:0.5PM567:Rh610=2:1PM567:Rh610=2:2PM567:Rh610=2:5PM567:Rh610=2:8PM567:Rh610=2:10PM567:Rh610=2:15PM567:Rh610=2:0

Fig. 4. The laser spectra of PM567:Rh610 dye mixture doped MPMMA sampleswith fixed donor concentration at 2�10�4 M and varying acceptor concentrations.

540 560 580 600 620 640 6600.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1 concentration ratio

PM567:Rh610=1:0 PM567:Rh610=1:2 PM567:Rh610=2:2 PM567:Rh610=5:2 PM567:Rh610=10:2 PM567:Rh610=15:2 PM567:Rh610=0:2

Inte

nsity

(a.u

.)

Wavelength (nm)

Fig. 5. The laser spectra of PM567:Rh610 dye mixture doped MPMMA sampleswith fixed acceptor concentration at 2�10�4 M and varying donor concentrations.

0 10 20 30 40 50 60 70 80 90

0

5

10

15

20

25

30

35

40

45

50

concentration ratioPM567:Rh610=2:0.5 K=39.6% PM567:Rh610=2:1 K=51.1% PM567:Rh610=2:2 K=63.7% PM567:Rh610=2:5 K=54.7% PM567:Rh610=2:8 K=47.4% PM567:Rh610=2:10 K=44.7% PM567:Rh610=2:15 K=23.9% PM567:Rh610=2:0 K=72.4%

Out

put e

nerg

y (m

J)

Input energy (mJ)

Fig. 6. The slope efficiencies of PM567:Rh610 dye mixture doped MPMMA sampleswith fixed donor concentration at 2�10�4 M and varying acceptor concentrations.

X. Li et al. / Journal of Luminescence 145 (2014) 202–207204

intensity of laser dyes with low efficiencies when directly pumpedby the commercial lasers. It should be noted that the donoremission peak also exists when the donor concentration is lowerthan 5�10�4 M, indicating that the energy transfer is not com-plete even for the lowest donor concentration used here. There-fore, the further increase of the donor concentration over5�10�4 M leads to the self-absorption within the donor mole-cules [30], causing the donor peak to disappear.

It is also shown in Figs. 2 and 3 that, if the concentration ratioof the donor and the acceptor is appropriate (for example, thesample with PM567:Rh610¼5:2 in Fig. 3), the width of thefluorescence spectra of the dye mixture doped samples can begreatly broadened relative to that of the samples solely dopedwith the donor or the acceptor. It creates the condition for thebroadband tunability of the dye mixture doped samples. Actually,broad tunability has been achieved by several research groupsbased on the energy transfer of dye mixtures [22,31,32].

3.2. Laser property investigation

The laser spectra were measured with the portable spectro-meter (HR4000, Ocean Optics). The laser spectra of the MPMMAsolid dye samples with fixed donor concentration and varyingacceptor concentrations, and fixed acceptor concentration andvarying donor concentrations are shown in Figs. 4 and 5, respec-tively. For the samples with fixed donor concentration at2�10�4 M and varying acceptor concentrations, the laser wave-length is red-shifted relative to the sample doped with the donoronly. The laser wavelength increases gradually with the increasingacceptor concentration. This is consistent with the red-shift of thefluorescence spectra of the samples with the increasing acceptorconcentration. The red-shift of the laser wavelength is probablyalso due to the self-absorption and re-emission effect. The resultsagree well with the results of Nhung et al. [18], who also reportedthe red-shift of the laser wavelengths with the increasing acceptorconcentrations in the RhB:P-red dye mixture doped xerogelmatrices. For the samples with fixed acceptor concentration at2�10�4 M and varying donor concentrations, the laser wave-length is also red-shifted with the increasing donor concentration.This is also consistent with the red-shift of the fluorescencespectra with the increasing donor concentration shown in Fig. 3.

The slope efficiencies of the MPMMA solid dye samples withfixed donor concentration and varying acceptor concentrations,

0 40 80 120 160 200 240 2800

20

40

60

80

100

120

140

160 concentration ratio

PM567:Rh610=1:0 k=57.2%PM567:Rh610=1:2 k=70.4%PM567:Rh610=2:2 k=54.4%PM567:Rh610=5:2 k=43.5%PM567:Rh610=10:2 k=36.6%PM567:Rh610=15:2 k=11.4%PM567:Rh610=0:2 k=9.03%

Out

put e

nerg

y (m

J)

Input energy (mJ)

Fig. 7. The slope efficiencies of PM567:Rh610 dye mixture doped MPMMA sampleswith fixed acceptor concentration at 2�10�4 M and varying donor concentrations.

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0

50

100

150

200

250

300

350

Acceptor concentration (1 ×10-4mol/L)

I 0d /

I d (a

.u.)

Fig. 8. Plot of I0d/Id vs. acceptor concentration for PM567:Rh610 dye mixture dopedMPMMA samples.

X. Li et al. / Journal of Luminescence 145 (2014) 202–207 205

and fixed acceptor concentration and varying donor concentra-tions are shown in Fig. 6 and 7, respectively. It is shown that theslope efficiency of the solid dye samples is closely related to thedonor:acceptor concentration ratios. For the samples with fixeddonor concentration, there is an optimum donor:acceptor concen-tration ratio to obtain the highest slope efficiency. When PM567:Rh610¼2:2, the highest slope efficiency is obtained as 63.7%. It iseasy to understand this phenomenon. When the acceptor con-centration is too low, the large distance between the donor andacceptor may inhibit the effective energy transfer. However, if theacceptor concentration is too high, the concentration quenchingeffect and the formation of nonradiative dimers will then lowerthe slope efficiency [29]. Therefore, there should be an optimumdonor:acceptor concentration ratio for the highest slope efficiency.

For samples with fixed acceptor concentration and varyingdonor concentrations, all the slope efficiencies of the dye mixturecodoped samples are higher than that of the sample doped withthe acceptor only. The results are consistent with Yang et al. [22]and Nhung et al. [18] who also demonstrated the laser efficiencyenhancement of the acceptor due to the energy transfer from thedonor. The highest slope efficiency is obtained with the concen-tration ratio of PM567:Rh610¼1:2 as 70.4%, which is nearly8 times that of the sample solely doped with the acceptor. Furtherincrease of the donor concentration will then decrease the slopeefficiency gradually. This phenomenon may be due to the cross-relaxation [20] between the donor molecules with the decreasedintermolecular separation as the donor concentration increases,thereby decreasing the energy for the acceptor considerably.

3.3. Energy transfer investigation

3.3.1. Energy transfer rate constantThe total energy transfer rate constant can be obtained using

the Stern–Volmer plot [20,24,25]

I0dId

¼ 1þ KSV A½ � ¼ 1þ KTτ0d A½ � ð1Þ

where I0d and Id are the fluorescence intensity of the donor in theabsence and presence of the acceptor, respectively, [A] is theacceptor concentration, KSV is the quenching rate constant, τ0d isthe fluorescence lifetime of donor in the absence of acceptor, andKT is the total energy transfer rate constant.

The Stern–Volmer plot of the MPMMA samples is shown inFig. 8. It is shown that the plot is linear up to a limiting acceptor

concentration of about 8�10�4 M. Beyond the limiting concen-tration, the plot develops into an upward curve. The resultsindicate that the dynamic quenching mechanism only holds forthe lower acceptor concentration range [33]. We processed thelinear fit in the linear acceptor concentration range, and obtainedthe quenching rate constant KSV as 1.05�104 M�1. With themeasured τ0d of 9.6 ns, the total energy transfer rate constant KT

was calculated as 1.09�1012 M�1s�1.The deviation of the Stern–Volmer plot from linearity may be

attributed to the ground state complex formation or the quenchingsphere of action (i.e. transient quenching) [33]. The ground statecomplex formation is discarded because no change is observed inthe absorption spectra of the samples with the presence of theacceptor [33]. Thus the deviation of the plot from linearity isrelated to the transient quenching.

According to the quenching sphere of action model [33,34],

I0dId

¼ expðKP A½ �Þ ð2Þ

which can rewrite as

lnðI0d=IdÞ ¼ VN0½A� ð3Þ

where I0d and Id are the same as in Eq. (1), Kp is the transientquenching constant, V is the volume of the quenching sphere incm3, N0 is the Avogadro's constant, and [A] is the acceptorconcentration.

Then the radius of the quenching sphere can be calculated as

R¼ ð3V=4πÞ1=3 ð4Þ

The plot of ln(I0d/Id) vs. acceptor concentration for the MPMMAsamples is shown in Fig. 9. The plot fits Eq. (3) very well. Itindicates that the transient quenching mechanism is taking placewhen the acceptor concentration is higher than the limitingconcentration [33]. The radius of the quenching sphere is calcu-lated as 16.26 Å using Eq. (4) from the slope of Fig. 9, which ismuch larger than the typical intermolecular separation (3–10 Å).Thus the dominant energy transfer mechanism should be longrange type, either the radiative transfer or the nonradiativetransfer due to long range dipole–dipole interaction.

The nonradiative energy transfer rate constant can be obtainedusing the following Stern–Volmer plot [20,25]

ϕ0d

ϕd¼ 1þ KNRτ0d A½ � ð5Þ

0 2 4 6 8 10 12 14 16

0

1

2

3

4

5

6

Acceptor concentration (1×10-4mol/L)

ln (I

0d/I d)

(a.

u.)

Fig. 9. Plot of ln(I0d/Id) vs. acceptor concentration for PM567:Rh610 dye mixturedoped MPMMA samples.

-2 0 2 4 6 8 10 12 14 16

1.000

1.005

1.010

1.015

1.020

1.025

Acceptor concentration (1×10-4mol/L)

φ 0d /

φd (

a.u.

)

Fig. 10. Plot of ϕ0d=ϕd vs. acceptor concentration for PM567:Rh610 dye mixturedoped MPMMA samples.

0 2 4 6 8 10 12 14 16

0.0

0.2

0.4

0.6

0.8

1.0

Tota

l ene

rgy

trans

fer e

ffic

ienc

y (a

.u.)

Acceptor concentration (1×10-4mol/L)

Fig. 11. Plot of total energy transfer efficiency vs. acceptor concentration forPM567:Rh610 dye mixture doped MPMMA samples.

0 2 4 6 8 10 12 14 16

0.000

0.005

0.010

0.015

0.020

0.025

Acceptor concentration (1×10-4mol/L)

Non

radi

ativ

e en

ergy

tran

sfer

ef

ficie

ncy

(a.u

.)

Fig. 12. Plot of nonradiative energy transfer efficiency vs. acceptor concentrationfor PM567:Rh610 dye mixture doped MPMMA samples.

X. Li et al. / Journal of Luminescence 145 (2014) 202–207206

where ϕ0d and ϕd are the quantum yields of the donor in theabsence and presence of the acceptor, respectively, [A] andτ0d isthe same as in Eq. (1), and KNR is the nonradiative energy transferrate constant.

The ϕ0d=ϕd can be obtained from the following equation [25]:

ηnr ¼ 1� ϕd

ϕ0dð6Þ

where ηnr is the nonradiative energy transfer efficiency, which canbe calculated with the theoretical expression for the long rangedipole–dipole interaction nonradiative transfer [35]

ηnr ¼ π1=2XexpðX2Þð1�erf XÞ ð7Þ

where X ¼ ½A�=½A�0 is the molar concentration of the acceptor,½A�0 ¼ 3000=ð2π3=2NR0Þ and erf X ¼ 2

π1=2

R X0 expð�t2Þdt.

The variation of ϕ0d=ϕd vs. acceptor concentration is shown inFig. 10. The nonradiative energy transfer rate constant KNR isobtained as 1.73�109 M�1 s�1 from the slope of Fig. 10.

Then the radiative energy transfer rate constant KR is obtainedusing the following equation [20]:

KR ¼ KT�KNR ð8Þ

The KR is obtained as 1.089�1012 M�1 s�1, which is threeorders of magnitude higher than the KNR, thus the dominantenergy transfer mechanism is the radiative type.

3.3.2. Energy transfer efficiencyThe total energy transfer efficiency ηT and the radiative energy

transfer efficiency ηr can be obtained as [15]

ηT ¼ 1� IdI0d

ð9Þ

ηr ¼ ηT�ηnr ð10ÞThe variation of ηT with the acceptor concentration is shown in

Fig. 11. It is shown that the ηT increases gradually with theincreasing acceptor concentration. When the acceptor concentra-tion is higher than 15�10�4 M, the ηT approaches 100%.

The nonradiative energy transfer efficiency is calculated usingEq. (7), and the variation of ηnr with the acceptor concentration isshown in Fig. 12. It can be seen that, the ηnr increases linearly withthe increasing acceptor concentration. The radiative transferefficiency ηr was obtained using Eq. (10). The variation of ηr=ηnrwith the acceptor concentration is presented in Fig. 13. It is shownthat the ηr=ηnr decreases gradually with the increase of acceptor

0 2 4 6 8 10 12 14 160

100

200

300

400

500

600

Acceptor concentration (1×10-4mol/L)

η r/η

nr (a

.u.)

Fig. 13. Plot of ηr/ηnr vs. acceptor concentration for PM567:Rh610 dye mixturedoped MPMMA samples.

X. Li et al. / Journal of Luminescence 145 (2014) 202–207 207

concentration. However, the ηr=ηnr is always higher than 80 for theacceptor concentrations investigated in this paper.

4. Conclusion

Laser dyes PM567 and Rh610 as energy donor and acceptorrespectively, were codoped into the ethanol modified poly (methylmethacrylate) solid dye matrices to enhance the properties of thesolid dye samples. Due to the energy transfer between the donorand the acceptor, the fluorescence intensity of the acceptor wasenhanced by up to 9 fold, and the slope efficiency of the solid dyesamples was enhanced by up to 8 times. The radiative andnonradiative energy transfer rate constants (KR and KNR) werecalculated using the Stern–Volmer plots. The KR was three ordersof magnitude higher than the KNR, indicating the dominance of theradiative energy transfer in the present system. Both the dynamicand transient quenching mechanism were found to exist in thepresent system with the deviation from linearity of the Stern–Volmer plot. The results demonstrate that the laser properties ofthe solid dye samples especially the laser efficiency can be greatlyenhanced with the energy transfer between the donor andacceptor dyes. This is useful for the laser dyes with low efficiencieswhen directly pumped by the common commercial lasers. Thiswill help to promote the development and extend the applicationrange of the solid dye lasers. Meanwhile, the broadening of thefluorescence line width of the dye mixture doped samples can beused for the broadband tuning operation of the solid dye lasers,and such work is in process now.

Acknowledgments

The authors gratefully acknowledge the financial support fromthe National Natural Science Foundation of China with Grant No.61275127.

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