chapter 3 the de-clustering influence of aluminium ions in...
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Chapter 3
The de-clustering influence of aluminium
ions on the emission features of Nd3+
ions
in PbO-SiO2 glasses
Nd3+
doped lead alumino silicate glasses with varying concentration of Al2O3
(from 5 to 10 mol%) have been synthesized. The IR and Raman spectral studies of
these glasses have indicated that there is a gradual increase in the depolymerization
of the glass network with increase in the concentration of Al2O3.The optical
absorption, luminescence spectra and fluorescence decay curves of these glasses were
recorded at room temperature. From these studies, the radiative parameters viz.,
spontaneous emission probability A, the total emission probability, the radiative
lifetime τ, the fluorescent branching ratio β of different transitions originated from
4F3/2 level of Nd
3+ ions have been evaluated. A clear increase in the quantum efficiency
and luminescence emission of the two prominent NIR bands of Nd3+
ions viz.,
4F3/2→
4I11/2, 13/2, is observed with increase in the concentration of Al2O3. The increase
has been attributed to the possible admixing of wavefunctions of opposite parities and
due to the declusterization of Nd3+
ions by Al3+
ions in the glass network.
The de-clustering influence of aluminium ions on the
emission features of Nd3+
ions in PbO-SiO2 glasses
3.1 Introduction
Aluminium containing silicate glasses are being widely used as low cost
optical connectors, dielectric and sealant materials for solid oxide fuel cells, in
actinide immobilization, as laser ion hosts, in optical lenses, seals and as in vivo
radiation delivery vehicles because of their high mechanical strength, high
electrical resistance and chemical durability [1-6]. Apart from these, it has been
widely accepted that aluminum ions produce greater enhancement on
fluorescence of all rare-earth ions embedded in the host material [7]; the
enhancement is ascribed to the association of RE ions with Al3+ ions in different
ways. The traditional interpretation, is that rare-earth ions will be preferably
partitioned by Al3+, forming Al‒O‒RE bonds, rather than sitting together to
form RE‒O‒RE bonds. Subsequently, the spacing among RE ions becomes
larger in the alumina-doped silica host rather than in the non–alumina-
containing host and facilitates for the enhancement of fluorescence [8].
Among various rare earth ions, Nd3+ ions are known due to their
significant emission transitions in NIR region. Out of three prominent emission
transitions of Nd3+ ions, the emission at 1.3 µm (4F3/2→4I13/2) is more important
because of its significant impact on telecommunications. In general, an efficient
73
host material for laser operation should exhibit large emission cross section to
provide high gain, long fluorescence lifetime to minimize pump losses incurred
from spontaneous emission, large absorption cross section at the pump
wavelength, good photothermal properties, absence of scattering centers and the
possibility to incorporate high concentration of rare earth ions. Aluminium
silicate glasses meet all the above requirements and can therefore be considered
as the most suitable glass for hosting Nd3+ ion with zero dispersion and low loss
at 1.3 µm wavelength. Majority of the studies on 1.3 µm emission are devoted
to Pr3+ doped glasses, whereas most of the studies on Nd3+ emission are
concentrated upon 1.06 µm emission [9-11].
Normally neodymium oxide is immiscible in silica glass and forms
aggregates or clusters in which cross relaxation can give rise to non-radiative
de-excitation of neodymium, resulting in very short lifetimes [12]. Different
research groups working in the field of luminescence have shown that the non-
radiative de-excitation of neodymium ions can be minimized and enhancement
of fluorescence is possible when Al is used as a co-dopant in the glasses
because aluminium ions disperse RE clusters, reduce inter-ionic interactions
and fluorescence quenching [7].
In this study we have synthesized PbO−Al2O3−SiO2: Nd2O3 glasses with
different contents of Al2O3 and investigated the influence of variation of Al2O3
74
concentration on 4F3/2→4I11/2,13/2 fluorescence transitions and fluorescence time
decays of Nd3+ ions in the titled glasses and evaluated the mechanism
responsible for the variation in the intensity of above transition in terms of
interactions between Al3+ ions and Nd3+ ions. The IR and Raman spectral
studies have also been included so as to asses some pre-structural information
on the glass network.
A particular composition (40-x) PbO–(5+x) Al2O3–54SiO2: 1.0 Nd2O3 (in
mol%) with three values of x ranging from 0 to 5.0, is chosen for the present study
The detailed compostions are as follows:
AN5: 40 PbO–5Al2O3–54SiO2: 1.0 Nd2O3
AN8: 37 PbO–8Al2O3–54SiO2: 1.0 Nd2O3
AN10: 35 PbO–10Al2O3–54SiO2: 1.0 Nd2O3
3.2 A brief review on the spectroscopic studies of Nd3+
ions in
various glass systems
The studies as such on spectroscopic properties of alumino silicate
glasses are very few. However, a brief review on recent studies on
luminescence properties of different other glass systems including some silicate
glass systems is presented here.
75
Pérez-Rodríguez et al. [13] have studied relevance of radiative transfer
processes on Nd3+ doped phosphate glasses for temperature sensing by means
of the fluorescence intensity ratio technique. Their studies the reabsorption
measurements in the samples with a higher Nd3+ content revealed that the
reliability of the sensing performance is compromised with the doping
concentration and the experimental conditions of the measurement. Pal et al.
[14] have reported fluorescence and radiative properties of Nd3+ ions doped
zinc bismuth silicate glasses. Their results have pointed out this glass system as
good candidate to be used in the development of photonics devices operating in
the near infrared spectral range. Sobczyk [15] has investigated temperature-
dependent luminescence and temperature-stimulated NIR-to-VIS up-conversion
in Nd3+-doped La2O3–Na2O–ZnO–TeO2 glasses. The results of this study
indicated that the investigated glasses are potentially applicable as a 1063 nm
laser host as well as an optical sensor for temperature measurements. Boetti et
al. [16] reported the results of spectroscopic investigations of Nd3 + single
doped and Eu3 +/Nd3 + co-doped phosphate glass for solar pumped lasers. This
study has indicated that although energy transfer from Eu3 + to Nd3 +occured, a
large Eu3 + concentration dependent quenching of Nd3 + fluorescence. This latter
process reported to decrease the radiative quantum efficiency of Nd3 +:4F3/2
emitting level. Gupta et al. [17] have studied the influence of bismuth on
76
structural, elastic and spectroscopic properties of Nd3+ doped Zinc–Boro-
Bismuthate glasses. These studies indicated that due to Bi2O3 incorporation
reduced host phonon energy and its high optical basicity effect remarkably
improved the Nd3+ luminescence properties such as emission intensity, quantum
yield and emission cross-section. Martin et al. [18] reported nanocrystal
formation using laser irradiation on Nd3+ doped barium titanium silicate glasses.
Evidence of nanocrystal formation induced by laser irradiation was confirmed
by optical spectroscopic, X-ray diffraction, scanning electron and atomic force
microscopy. Lu et al. [19] reported crystallization, structure and fluorescence
emission of Nd3+- and Yb3+-doped NCS transparent glass-ceramics. In this
report it was said that there is strong fluorescence emission in the Nd3+-and
Yb3+-doped NCS glass-ceramics when compared with the singly ion doped
glasses. Sola et al. [20] studied the stress-induced buried waveguides in the
0.8CaSiO3–0.2Ca3(PO4)2 eutectic glass doped with Nd3+ ions. The objective of
this study was to characterize and to evaluate in what extent their optical
properties could be modified by the waveguide fabrication process.
Brahmachary et al. [21] have investigated spectroscopic properties of Nd3+
doped zinc-alumino-sodium-phosphate (ZANP) glasses. Mahamuda et al. [22]
have studied the spectroscopic properties and luminescence behavior of Nd3+
doped zinc alumino bismuth borate glasses. From these studies it was
77
concluded that 1 mol% of Nd3+ ion concentration is optimum for zinc alumino
bismuth borate glasses to generate a strong laser emission at 1060 nm.
Kawamura et al. [23] have reported the extraction of Nd3+-doped LiYF4
phosphor from sol–gel-derived oxyfluoride glass ceramics by hydrofluoric acid
treatment. The photoluminescent (PL) properties were investigated for the
sample before and after HF treatment. The results indicated that the Nd3+ ions
were predominantly incorporated in LiYF4, and the extraction of LiYF4
crystallites was successfully carried out without changing the PL properties of
Nd3+ ions. da Silva et al. [24] have investigated the frequency upconversion in
Nd3+ doped PbO–GeO2 glasses containing silver nanoparticles. Their results
indicated that the nucleation of silver NPs in Nd3+-doped PGO glasses
contributes to increase the UC efficiency. Fu et al. [25] have reported studies on
single-mode waveguides generated in Nd3+-doped silicate glass by nickel ion
irradiation. Shanmugavelu et al. [26] have studied optical properties of Nd3+
doped bismuth zinc borate glasses.
Surendra Babu et al. [27] have recently reported the results of their
studies on 1.06 µm emission in Nd3+-doped alkali niobium zinc tellurite glasses.
From this study they have concluded that 4F3/2→4I11/2 is the probable lasing
transition excited with low threshold power. Cankaya and Sennaroglu [28] have
reported lasing emission of Nd3+ ions in TeO2–WO3 glasses at 1.37 µm. In this
78
report the authors have claimed to have measured the luminescence efficiency
as much as 78%. Saleem et al. [29] have reported optical absorption and near
infrared emission properties of Nd3+ ions in alkali lead tellurofluoroborate
glasses. In this study the authors have evaluated total radiative transition
probabilities (AT), stimulated emission cross-sections (σE) and gain bandwidth
parameters (σE × ∆λP) and compared with the earlier reports. Zhong et al. [30]
have reported 2.7 µm emissions of Nd3+, Er3+ codoped tellurite glass. In this
study the authors have observed the enhanced mid infrared emission due to the
co-doping. Verma et al. [31] have studied effect of modifiers (BaF2 BaCl2 and
BaCO3) and heat treatment on the fluorescence bands of Nd3+ ions in TeO2
glasses. Their study has indicated that the BaCl2 modified glass exhibits
maximum upconversion intensity among the three modifiers. From the
temperature dependent fluorescence studies of these glasses the authors have
concluded that Nd3+ doped tellurite glass can be used as a temperature sensor.
Courrol et al. [32] have studied spectral properties of lead fluoroborate
glasses doped with Nd3+. Wilhelm et al. [33] have reported the fluorescence life
time enhancement of Nd3+-doped sol–gel glasses by Al–codoping and CO2-
laser processing. Karthikeyan and Mohan [34] have reported the structural,
optical and glass transition studies on Nd3+ doped lead bismuth borate glasses.
Annapurna et al. [35] have investigated the NIR emission and upconversion
79
luminescence spectra of Nd3+:ZnO–SiO2–B2O3 glasses. Saisudha and
Ramakrishna [36] have found large radiative transition propabilities in bismuth
borate glasses doped with Nd3+ ions. Shen et al. [37] have reported the
compositional effects and spectroscopy of rare earths (Er3+, Tm3+, and Nd3+) in
tellurite glasses. Kumar et al. [38] have explored the stimulated emission and
radiative properties of Nd3+ ions in barium fluorophosphate glass containing
sulphate. Chen et al. [39] have studied ion-implanted waveguides in Nd3+ doped
silicate glass and Er3+/Yb3+ co-doped phosphate glass. Kam and Buddhudu [40]
have studied Luminescence enhancement in (Nd3++Ce3+) doped SiO2: Al2O3
sol-gel glasses. Rosa-Cruz et al. [41] have reported the results of their study on
spectroscopic characterization of Nd3+ ions on barium fluoroborophosphate
glasses. Fernandez et al. [42, 43] have evaluated the upconversion losses in Nd-
doped fluoroarsenate glasses. Surana et al. [44] have investigated the Laser
action in neodymium-doped zinc chloride borophosphate glasses. Vijaya
Prakash reported [45] his results of absorption spectral studies of Pr, Nd, Sm,
Dy, Ho and Er ions doped in NASICON type phosphate glass, Na4AlZnP3O12.
Rao et al. [46] have reported luminescence properties of Nd3+: TeO2–B2O3–
P2O5–Li2O glass. Xiang et al. [47] have studied the up-conversion emission in
violet from yellow in Nd3+: SiO2–TiO2–Al2O3 sol-gel glasses. Bouderbala et al.
[48] have reported the results of their studies on infrared and visible room
80
temperature fluorescence induced by continuous laser excitation of new Nd3+:
phosphate glasses. Cassanjes et al. [49] have investigated Raman scattering,
differential scanning calorimetry and Nd3+ spectroscopy in alkali niobium
tellurite glasses. Mehta et al. [50, 51] have investigated the spectroscopic
properties including ESR of Nd3+ doped phosphate and borate glasses. Kumar
and Bhatnagar [52] have reported the effect of modifier ions on the covalency
of Nd3+ ions in cadmium borate glasses. Srinivasa Rao et al. [53] have reported
the physical and absorption properties of Nd3+ doped mixed alkali fluoro-
borophosphate optical glasses. Ajit Kumar et al. [54] have reported the
spectroscopic parameters of Nd3+ ion in phosphate glasses. Joshi and Lohani
[55] have investigated the non-radiative energy transfer from Tm3+ to Ho3+ and
Nd3+ in zinc phosphate glass. Dawar et al. [56] have studied the optical and
acousto-optical properties of Nd: phosphate glasses. Ning Lei et al. [57] have
fabricated Ti: sapphire laser pumped Nd: tellurite glass laser. Pozza et al. [58]
have investigated the absorption and luminescence spectroscopy of Nd3+ and
Er3+ in a zinc borate glass. Ratnakaran and Buddhudu [59] have reported the
optical absorption spectra and laser analysis of Nd3+ ions in fluoroborate
glasses. Sen and Stebbins [60] have studied structural role of Nd3+ in SiO2 glass
using NMR studies. Ebendorff et al. [61] have studied the spectroscopic
properties of Nd3+ ions in phosphate glasses.
81
3.3 Results and Discussion
In the presence of modifiers SiO2 participates in the glass network with
meta, pyro and ortho−silicates in the order: [SiO4/2]0 (Q4), [SiO3/2O]− (Q3),
[SiO2/2O2]2−(Q2), [SiO1/2O3]
3−(Q1) and [SiO4]4− (Q0) [62]. Earlier NMR studies
on aluminium silicate glasses have indicated that aluminium ions occupy
mainly tetrahedral (AlO4) and octahedral (AlO6) sites [63].
2Al2O3 → [Al3+] o + 3[AlO4/2]t
The AlO4 tetrahedrons enter the glass network and alternate with SiO4
tetrahedrons, whereas octahedral Al3+ induce bonding defects in the glass
network and participate in the declusterization of Nd3+ ions. Recently, it was
demonstrated by Schmucker and Schneider [64] using NMR studies that the
edge-sharing [AlO4] tetrahedra also participate in inducing bonding defects in
the silicate glass network. The oxygen triclusters of such units (oxygen ion
bonded to two [AlO4] and one [SiO4] or one [AlO4] and two [SiO4]) take part in
inducing bonding defects in the glass containing Al2O3 and SiO2. PbO,
normally in the concentration range used in the present study acts
as a modifier and as a result Si-O-Si and Si-O-Al bonds are cleaved in
succession. Such behaviour also lead to a de-polymerization of the glass
network.
82
From the measured values of the density and average molecular weight
M of the samples, various other physical parameters such as Nd3+ ion
concentration Ni, mean Nd3+ ion separation Ri and molar volume for all the
glass samples were evaluated and presented in Table 3.1. The dependence of
density d on the concentration of Al2O3 for all the titled glasses shows slight
decrement with increasing Al2O3 content. The decrease of density can be
understood due to the replacement of PbO by Al2O3.
Table 3.1 Physical parameters of PbO−Al2O3−SiO2 glasses doped with different concentrations of Nd2O3.
Physical parameter↓ Glass →
Nd3+ series AN5 AN8 AN10
Density d (g/cm3)
4.6218 4.4147 4.3014
Refractive index
1.647 1.646 1.645
Nd3+ion conc. Ni (x1020 ions/cm3)
2.14 2.10 2.09
Interionic distance Ri (Å)
16.72 16.82 16.86
Polaron radius Rp ( Å ) 6.74 6.78 6.79
Field Strength Fi (1014, cm-2)
4.41 4.35 4.33
83
DSC studies on Nd2O3 doped PbO−Al2O3−SiO2 glasses mixed with
different concentrations of Al2O3 have been carried out. All DSC traces exhibit
typical glass transition (Tg) with the inflection point between 850–870 K; the
glass transition temperature decreases slightly with increasing Al2O3 content. At
about 1240 oC, the process of crystallization begins and all the traces exhibited
well defined exothermic peaks at TC.
To observe the mass change effects during heating process, we have also
recorded thermal gravimetric traces for all the samples; TG traces for two of the
samples along with corresponding DSC traces are shown. The thermal
gravimetric analysis for all the samples indicated that upto 1200 K virtually no
change in the mass of the samples. In Fig. 3.1 DSC and TG traces for the glass
AN5 are presented. In the inset of Fig. 3.1 we have presented the variation of
variation of Tc-Tg (a parameter that gives the information on thermal stability
of the glass) is found to be decreased slightly with the concentration of Al2O3. It
may be noted here that DSC traces of all the three series of glasses viz.,
PbO−Al2O3−SiO2:Nd3+/Dy3+/Yb3+ exhibited a similar trend. In view of this, the
DSC patterns PbO−Al2O3−SiO2:Dy3+/Yb3+ were not presented in the subsequent
chapters.
84
Fig. 3.1 DSC and TG Traces for the glass AN5. Inset shows the variation of Tc-Tg with the concentration of Al2O3.
The optical absorption spectra of PbO−Al2O3−SiO2: Nd2O3 glasses
recorded at room temperature in the wavelength region 300-2000 nm exhibited
conventional absorption bands corresponding to the following electronic
transitions [65]
4I9/2 → 2P1/2, 2D3/2+
4G11/2, 4G9/2+
4G7/2, 4G5/2,
2H11/2, 4F9/2,
4F7/2, 4F5/2 and
4F3/2
The pattern of absorption spectra for all the three glasses remains the same;
however, considerable variations in the peak positions and the intensity of these
bands have been observed (Fig. 3.2).
85
Fig. 3.2 Optical absorption spectra of PbO-Al2O3 -SiO2: Nd2O3 glasses in the visible region (all transitions are from 4I9/2).
2.0
3.0
4.0
5.0
6.0
7.0
8.0
400 450 500 550 600 650 700 750 800 850 900
2P1/2
2D3/2
4G9/2
4G7/2
4G5/2
2H11/24F9/2
4F7/2
4F5/2
4F3/2
AN5
AN10
AN8
Wavelength(nm)
Abs
orbt
ion
coef
fici
ent (
cm-1
)
86
The experimental oscillator strengths (OS) of the absorption transitions
were estimated from the spectra for all the three rare earth ion doped glasses in
terms of the area under absorption peaks. The procedure of fitting of the
calculated OS to those evaluated from the experimental spectra is described in
Ref.[66]. A set of matrix equations (which includes the U2, U4, and U6 matrices,
the matrices of the experimental OS and the energies of the corresponding
transitions) have been solved to minimize the difference between the calculated
fcal and observed fobs OS. The quality of fitting is determined by the root mean
squared deviation (RMS) defined as [67], and presented in Table 3.2 for all the
three glasses. The deviations indicate reasonably good fitting between theory
and experiment, demonstrating the applicability of JO theory. The values of
Ωλ are found to be in the following order for the three glasses Ω2 > Ω6 > Ω4 and
found to be consistent with the some recently reported values [68, 69]. For
evaluating the JO parameters from the absorption spectra the baseline was
drawn in such a way to remove the background in all absorption spectra, we
mean to leave only those features corresponding to the 4f-4f transitions, which
are clearly seen on the top of the background. Then such a baseline was
subtracted from the spectrum, and the spectrum modified in this way was used
for calculations of the experimental OS.
(3.1) ( )
31
2
exp
−
−=∑
=
N
ff
RMS
N
i
i
calc
i
87
Table 3.2 The absorption band energies, the oscillator strength for the transitions of Nd3+ ion PbO-Al2O3–SiO2 glasses. All transitions are from the ground state 4I9/2
Transition
AN5 AN8 AN10
Barycenter (cm-1)
fexp (×10-6)
fcal
(×10-6) Barycenter (cm-1)
fexp (×10-6)
fcal
(×10-6) Barycenter (cm-1)
fexp (×10-6)
fcal
(×10-6)
4I9/2 → 4F3/2 11358 3.2433 2.5644 11363 4.4655 2.9729 11358 1.4220 1.1288 4F5/2 12381 13.6470 11.7574 12336 15.5183 13.2551 12402 7.9474 7.0369 4F7/2 13403 11.3087 12.3779 13398 12.6297 13.9120 13399 7.4073 7.9067 4F9/2 14622 0.8325 1.6259 14620 1.1444 1.8298 14642 0.6452 1.0328
2H11/2 15735 0.55 0.3541 15686 0.4583 0.3979 15954 0.1115 0.2243 4G5/2 17113 34.7772 34.6050 17121 40.3518 40.1105 17120 24.8989 24.8292 4G7/2 18911 3.7539 5.9892 18912 3.7869 6.9099 18899 2.6207 3.5077 4G9/2 19575 1.1836 2.3194 19624 0.9381 2.6592 19552 0.6464 1.2909
2D3/2, 4G11/2
,
4G9/2 21091 1.6681 1.4947 21210 2.3500 1.7193 20991 0.5374 0.7828
2P1/2, 2D5/2 23141 1.0995 0.5657 23210 0.7121 0.6700 23213 0.4066 0.1776
rms deviation ±1.3349 ±1.7984 ±0.6150
JO parameters Ω2 Ω4 Ω6 Ω2 Ω4 Ω6 Ω2 Ω4 Ω6
( x 1020, cm2) 13.94 3.37 13.58 12.16 2.81 12.08 9.36 0.56 8.42
88
According to the Judd–Ofelt theory, crystal field parameter that determines the
symmetry and distortion related to the structural change in the vicinity of Nd3+ ions. In
the present context, this may be understood as follows: the larger the degree of disorder
or depolymerization in the glass network, the larger is the average distance between Si–
O–Si, Si–O–Pb chains causing the average Nd–O distance to increase. Such increase in
the bond lengths produces weaker field around Nd3+ ions leading to a low value of Ω2 for
the glass mixed with 10.0 mol% of Al2O3 [68]. Additionally the variations in the
concentration of silicate groups with different number of non-bridging oxygens, as
discussed before, also play an important role in the variation of value of Ω2.
The luminescence spectra of Nd3+ doped glasses excited at 582 nm recorded at
room temperature in the spectral range 0.95 to 1.6 µm region are shown in Fig. 3.3; the
spectra exhibited bands due to 4F3/2→4I11/2 (at 1.06 µm) and 4F3/2→
4I13/2 (at 1.3 µm)
transitions. Further a gradual growth of these bands is clearly observed with increase in
the concentration of Al2O3. From these spectra, various radiative parameters viz.,
spontaneous emission probability, A, the total emission probability, AT, the radiative
lifetime τ, the fluorescent branching ratio β of different transitions originated from 4F3/2
level of Nd3+ ions have been evaluated and presented in Table 3.3.
The fluorescence decay curve of the 4F3/2 excited level of Nd3+ doped glasses is
shown in Fig. 3.4; the curves viewed to be double exponential with a smaller (~ 20%) and
a larger (~ 80%) fast decay component (τfd). The evaluated lifetimes with possible errors
89
are presented in Table 3.4. The lifetimes, both experimental and calculated, were found to
be in the increasing order with increase in the concentration of Al2O3.
Fig. 3.3 Photoluminescence spectra of PbO-Al2O3 -SiO2: Nd2O3 glasses in the NIR region excited at 582 nm.
950 1050 1150 1250 1350 1450 1550 1650
4F3/2→ 4I11/2
4F3/2→ 4I13/2
Wavelength(nm)
PL I
nten
sity
(ar
b. u
nits
)
AN5 AN10AN8
90
Table 3.3 Various radiative properties of transitions of Nd3+ ions in PbO–Al2O3–SiO2 glasses
Transition AN5 AN8 AN10
A (s-1) β (%) A (s-1) β (%) A (s-1) β (%)
4F3/2 → 4I9/2 1796 29.38 1634 27.29 1657 28.01
→4I11/2 3499 57.26 3538 59.09 3731 63.08
→4I13/2 774 12.67 768 12.83 500 8.45
→4I15/2 42 0.69 47 0.78 27 0.46
τ = 164 µs τ = 167 µs τ =169 µs
Table 3.4 Summary of the data on life measurements of 4F3/2 excited level
Glasses Life time Nd doped samples; λexcitation = 582 nm and λemission = 1064nm
Quantum efficiency
η%
measured (µs) Calculated (µs) τcal
χ2 (possible error in τexpt ) τfd τsd
AN5 67 (21%) 171 (79%) 164 1.6 72.5
AN8 69 (21%) 187 (79%) 167 1.5 76.6
AN10 73 (19%) 191 (81%) 169 1.6 78.1
The Infrared spectra of PbO Al2O3 SiO2: Nd2O3 glasses (Fig. 3.5) exhibited conventional
bands at about 1025 cm-1 due to Si-O-Si asymmetric vibrations, 760 cm-1 due to Si-O-Si
symmetric vibrations and at about 450 cm-1 due to Si-O-Si rocking motion [62, 70].
Incidentally, the vibrational frequency of Al O stretching in AlO4 structural units is
found to exhibit band at about 750 cm-1 and band due to AlO6 structural units lie
91
Fig.3.4 Decay curves of Nd3+ (4F3/2→
4I11/2) doped PbO−Al2O3−SiO2 glasses recorded at room temperature excited at 582 nm.
at about 450 cm-1 [71]. Hence, it is quite likely that tetrahedral Al ion to cross link
with the neighbouring Si-O-Si structural units and form Al-O-Si linkages. Hence the
band observed at 760 cm-1 may be considered as the band due to Si-O-Al linkages. The
band due to the vibrations of PbO4 structural units about 470 cm-1 is also present in these
glasses. With increase in the concentration of Al2O3, the intensity of the bands due to Si-
O-Si asymmetric vibrations and Si-O-Si rocking motion increases at the expense of band
due to Si-O-Si/ Si-O-Al symmetric vibrations. A visible increase in the intensity of the
band due to AlO6 structural units is also observed with the increase in the concentration
of Al2O3. Such features of the spectra indicate an increasing concentration of Al3+ ions
that act as modifiers with increasing content of Al2O3 in the glass matrix.
AN8
AN10
AN5
Inte
nsity
(cy
cles
/s)
103
104
Time (x106, µs)0.32 0.72 1.12 1.52
92
Fig. 3.5 IR spectra of PbO-Al2O3 -SiO2: Nd2O3 glasses.
400500600700800900100011001200
Si–O
–Si a
sym
met
ric
units
Si–O
–Si s
ymm
etri
c/ A
lO 4
uni
ts
Si–O
–Si r
ocki
ng
mot
ions
/AlO
6 un
its
Sym
met
rica
l ben
ding
vi
brat
ions
of
PbO 4
Tra
nsm
ittan
ce %
Wavenumber (cm-1)
AN5
AN10
AN8
93
The Raman spectra of PbO–Al2O3–SiO2:Nd2O3 glasses (Fig.3.6) exhibited bands
at 1050 cm-1 and at 815 cm-1 due to Si–O–Si asymmetric modes and symmetric vibrations
of SiO4 tetrahedra respectively. In the region of Si-O-Si symmetric modes, Al–O
stretching vibrations of Al tetrahedral coordination are also possible. The spectra also
exhibited a band at 550 cm-1 attributed to the bridging oxygen breathing mode in (Si, Al)
three-membered rings and another band at 475 cm-1 due to Si-O-Si rocking vibrations
[72]. The spectra also exhibited a weak envelope at about 330 cm-1 due to the vibrations
of PbO4 units [73]. As the concentration of Al2O3 increases a noticeable enhancement in
the intensity of the bands due to Si–O–Si asymmetric modes and Si-O-Si rocking
vibrations of SiO4 tetrahedra is observed at the expense of the band due to symmetric
vibrations of SiO4. Such changes clearly indicate an increasing disorder in the glass
network with increasing content of Al2O3. Thus both IR and Raman spectra of the studied
glasses suggests that there is an increase in the concentration of Al3+ ions that act as
modifiers (which may de-cluster Nd3+ ions) with increase in the concentration of Al2O3 in
the glass network.
94
Fig. 3.6 Raman spectra of PbO-Al2O3 -SiO2: Nd2O3 glasses.
Neodymium oxide normally exhibits immiscible tendency in silica glass and as a
result it forms aggregates or clusters in which cross relaxation can give rise to non-
radiative de-excitation of neodymium, resulting in very short lifetimes. Comparatively
weak fluorescence intensity and short emission lifetime observed for glass AN5 indicates
possible formation of more concentration of Nd3+ clusters that are responsible for
luminescence quenching in this glass matrix [9]. The observed increase of PL peak
intensity with increase in the Al2O3 concentration clearly suggests that Al increases PL
200 400 600 800 1000 1200Wavenumber (cm-1)
Si-O
-Si r
ocki
ng
grou
ps/A
lO6
units
(Si,
Al)
- T
hree
mem
bere
d ri
ngs
Si-O
-Si b
endi
ng
grou
ps/A
lO 4
units
Ram
an in
tens
ity (
a.u.
)
AN5
AN8
Si-O
-Si
stre
tchi
ng
grou
ps
PbO
4 te
trag
onal
pyr
amid
s
AN10
95
output indicating the possibility of admixing of wavefunctions of opposite parities which
lead to increase the radiative probabilities of all the f-f transitions [74]. Among the two
life time components observed from the decay curves, the value of τfd is found to be
virtually invariant while τsd is found to increase significantly with increase in the
concentration of Al2O3.The fast decay component is obviously due to the emission from
clusterized Nd3+ ions which cross relax (concentration quenching) and give rise to non-
radiative de-excitation of neodymium ions. The slow decay component can be attributed
to the emission from Nd3+ ions that are uniformly dispersed in the silica matrix; the
increasing value of this component with increase in the concentration of Al2O3 indicates
aluminum ions gradually disperse Nd3+ ions uniformly in the glass matrix and reduces
fluorescence quenching due to cross-relaxation. Branching ratio ‘β’ (that defines the
luminescence efficiency of the transition) of the orange emission due to 4F3/2→4I11/2
transition, among various transitions originated from 4F3/2, is found to be the highest
(~63%) for the glass AN10 and it is ∼ 57% for the glass AN5.
The quantum efficiency (η = τexp/τcal), defined as the radiative portion of the total
relaxation rate of a given energy level is found to be increasing (Table 3.3) with increase
in the concentration of Al2O3 (τexp is taken as an average of two components). As has
been discussed earlier, the degree of dispersion of Nd3+ ions is higher in the glass
containing higher concentration of Al2O3 which lead to high non–radiative losses causing
higher value of η.
96
3.4 Conclusions
Lead alumino silicate glasses of the composition (40-x) PbO–(5+x) Al2O3–
54SiO2: 1.0 Nd2O3 (in mol%) with three values of x ranging from 0 to 5.0 were prepared.
IR, Raman, optical absorption, photoluminescence and luminescence decay have been
studied.
(i) The IR and Raman spectral studies have indicated that there is a gradual
depolymerization of the glass network with increase in the concentration of
Al2O3.
(ii) The optical absorption spectra of these glasses exhibited bands due to
4I9/2 → 2P1/2, 2D3/2+
4G11/2, 4G9/2+
4G7/2, 4G5/2,
2H11/2, 4F9/2,
4F7/2, 4F5/2 and
4F3/2
transitions. The spectra have been characterized by JO theory and a reasonable
matching between experimental and theoretical oscillator strengths could be
achieved.
(iii) The luminescence spectra of these glasses excited at 582 nm exhibited two
prominent transitions viz., 4F3/2→4I11/2,13/2 in the spectral region 950 to 1600
nm. An increase in the PL output of these transitions is observed with increase
in the concentration of Al2O3.
(iv) The quantitative analysis of these results has revealed that the Al3+ ions cause
declusterization of Nd3+ ions and thereby decrease the luminescence quenching
due to cross relaxation.
97
References
[1] S.L. Lin, C.S. Hwang, J. Non-Cryst. Solids 202 (1996) 61
[2] J.E. Shelby, J.T. Kohli, J. Am. Ceram. Soc. 73 (1990) 39
[3] Y. Gandhi, M. V. Ramachandra Rao, Ch. Srinvasa Rao, T. Srikumar, I. V. Kityk and N. Veeraiah, J. Appl. Phys. 108 (2010) 023102
[4] T.M. Gross, Ceram. Trans. 230 (2012) 113
[5] A.R. Hanifi, A. Genson, M.J. Pomeroy, S. Hampshire, J. Am. Ceram. Soc. 95 (2012) 3355
[6] T.M. Hau, R. Wang, X. Yu, D. Zhou, Z. Song, Z. Yang, X. He, J. Qiu, J. Phys.
Chem. Sol. 73 (2012) 1182
[7] J. Laegsgaard, Phys. Rev. B 65 (2002) 174114
[8] M. Gu, Q. C. Gao, S.M. Huang, X.L. Liu, B. Liu, C. Ni, J. Lumin. 132 (2012) 2531
[9] T. Satyanarayana, M.G. Brik, N. Venkatramaiah, I.V. Kityk, K.J. Plucinski V. Ravi Kumar and N. Veeraiah, J. Am. Ceram. Soc. 93 (2010) 2004
[10] B. Burtan, Z. Mazurak, J. Cisowski, M. Czaja, R. Lisiecki, W. Ryba-Romanowski, M. Reben, J. Wasylak, Opt. Mater. 34 (2012) 2050
[11] A.A. Andrade, V. Pilla, S.A. Lourenço, A.C.A. Silva, N.O. Dantas, Chem. Phys.
Lett. 547 (2012) 38
[12] S. Shinoya, W. M. Yen, Phosphor Handbook, CRC Press, Boca Raton, 1999
[13] C. Pérez-Rodríguez, L.L. Martín, S.F. León-Luis, b, I.R. Martín, b, K. Kiran Kumar, C.K. Jayasankar, Sens. Actuators B: Chem., 195 (2014) 324
[14] I. Pala, A. Agarwal, S. Sanghi, M.P. Aggarwal, S. Bhardwaj, J. Alloys Compd. 587 (2014) 332
[15] Marcin Sobczyk, J. Quant. Spect. Rad. Transfer, 119 (2013) 128
[16] N.G. Boetti, D. Negro, J. Lousteau, F.S. Freyria, B. Bonelli, Silvio Abrate, Daniel Milanese, J. Non-Cryst. Solids, 377 (2013) 100
[17] G. Gupta, A.D. Sontakke, P. Karmakar, K. Biswas, S. Balaji, R. Saha, R. Sen, K. Annapurna, J. Lumin. 149 (2014) 163
98
[18] L.L. Martin, S. Ríos, I.R. Martín, c, P. Haro-González, J.M. Cáceres, A. Hernández-Creuse, J. Alloys Compd. 553 (2013) 35
[19] A. Lu, X. Hu, Y. Lei, Z. Luo, X. Li, Ceram. Intern., 40 (2014) 11
[20] D. Sola, J. Martínez de Mendibil, J.R. Vázquez de Aldana, G. Lifante, R. Balda, A.H. de Azae, P. Penae, J. Fernándeza, Appl. Surface Sci. 278 (2013) 289
[21] K. Brahmachary, D. Rajesh, S. Babu, Y.C. Ratnakaram, J. Mol. Struc. 1064 (2014) 6
[22] Sk. Mahamuda, K. Swapna, A. Srinivasa Rao, M. Jayasimhadri, T. Sasikala, K. Pavani, L. Rama Moorthy, J. Phys. Chem. Solids, 74 (2013) 1308
[23] G. Kawamura, R. Yoshimura, K. Ota, S.Y. Oh, H. Muto, T. Hayakawa, A. Matsuda, Opt. Mater. 35 (2013) 1879
[24] Diego S. da Silva, , Thiago A.A. de Assumpção, Luciana R.P. Kassab, Cid B. de Araújo, J. Alloys Compd. 586 (2014) S516
[25] Gang Fu, Shiling Li, Xifeng Qin, Xiuquan Zhang, Nucl. Instr. Meth. Phys. Res. Sec.
B: Beam Int. Mater. Atoms, 315 (2013) 325
[26] B. Shanmugavelu, V. Venkatramu, V.V. Ravi Kanth Kumar, Spectrochim. Acta
Part A: Mole. Biomole. Spec. 122 (2014) 422
[27] S. Surendra Babu, R. Rajeswari, K. Jang, C. Eun Jin, K. Hyuk Jang, H. Jin Seo, C.K. Jayasankar, J. Lumin. 130 (2010) 1021
[28] H. Cankaya, A. Sennaroglu, Appl. Phys. B 99 (2010) 121
[29] S.A. Saleem, B.C. Jamalaiah, J.S. Kumar, A.M. Babu, L.R. Moorthy, M. Jayasimhadri, K. Jang, (...), J.H. Jeong, Solid State Sci. 11 (2009) 2093
[30] H. Zhong, B. Chen, G. Ren, L. Cheng, L. Yao, J. Sun, J. Appl. Phys. 106 (2009) 083114
[31] R.K. Verma, K. Kumar, S.B. Rai, Spectrochim. Acta - Part A 74 (2009) 776
[32] L.C. Courrol, L.R.P. Kassab, V.D.D. Cacho, S.H. Tatumi, N.U. Wetter, J. Lumin. 102 (2003) 101
[33] B. Wilhelm, V. Romano, H.P. Weber, J. Non-Cryst. Solids 328 (2003) 192
[34] B. Karthikeyan, S. Mohan, Physica B 334 (2003) 298
99
[35] K. Annapurna, R.N. Dwivedi, P. Kundu, S. Buddhudu, Mater. Lett. 57 (2003) 2095
[36] M.B. Saisudha, J. Ramakrishna, Opt. Mater. 18 (2002) 403
[37] S. Shen, A. Jha, E.Zhang, S.J. Wilson, Comptes Rendus Chimie 5 (2002) 921
[38] G.A. Kumar, A. Martinez, E.De La Rosa, J. Lumin. 99 (2002) 141
[39] Feng Chen, Xue-Lin Wang, Xi-Shan Li, Li-Li Hu, Qing-Ming Lu, Ke-Ming Wang, Bo Rong Shi, Ding-Yu Shen, Appl. Surface Science 193 (2002) 92
[40] C.H. Kam, S. Buddhudu, Opt. Lasers Engg. 35 (2001) 11
[41] E. De la Rosa-Cruz, GH.A. Kumar, L.A. Diaz-Torres, A. Martinez, O. Barbosa Garcia, Opt. Mater. 18 (2001) 321
[42] J. Fernandez, R. Balda, M. Sanz, L.M. Lacha, A. Oleagha, J.L. Adam, J. Lumin. 94 (2001) 325
[43] R. Balda, L.M. Lacha, A. Mendioroz, M. Sanz, J. Fernandez, J.L. Adam, M.A. Arriandiaga, J. Alloys Comp. 323 (2001) 255
[44] S.S.L. Surana,Y.K. Sharma, S.P. Tandon, Mater. Sci. Engg. B 83 (2001) 204
[45] G.V. Prakash, Mater. Lett. 46 (2000) 15
[46] T.V.R. Rao, R.R. Reddy, Y. Nazeer Ahammed, M. Parandamaiah, N. Sooraj Hussain, S. Buddhudu, K. Purandar, Infrared Phys. & Tech. 41 (2000) 247
[47] Q. Xiang, Y. Zhou, Y.L. Lam, Y.C. Chan, C.H. Kam, B.S. Ooi, H.X. Zhang, S. Buddhudu, Mater. Res. Bull. 35 (2000) 571
[48] M. Bouderbala, H. Mohmoh, A. Bahtat, M. Bahtat, M. Ouchetto, M. Druetta, B. Eloudai, J. Non-Cryst. Solids 259 (1999) 23
[49] Fabia C. Cassanjes, Younes Messaddeq, Luiz F.C. de Oliveria, Lilia C. Courrol, Laercio Gomes, Sidney J.L. Ribeiro, J. Non-Cryst. Solids 247 (1999) 58
[50] V. Mehta, G. Aka, A.L. Dawar, A. Mansingh, Opt. Mater. 12 (1999) 53
[51] V. Mehta, D. Gourier, A.L. Dawar, A. Mansingh, Solid State Commun. 109 (1999) 513
[52] V.V. Ravi Kanth Kumar, Anil K. Bhatnagar, Opt. Mater. 11 (1998) 41
100
[53] A. Srinivasa Rao, J. Lakshmana Rao, Y. Nazeer Ahammed, R. Ramakrishna Reddy, T.V. Ramakrishna Rao, Opt. Mater. 10 (1998) 129
[54] G. Ajit Kumar, P.R. Biju, C. Venugopal, N.V. Unnikrishnan, J. Non-Cryst. Solids 221 (1997) 47
[55] B.C. Joshi, R. Lohani, J. Non-Cryst. Solids 215 (1997) 103
[56] A.L. Dawar, V. Mehta, Abhai Mansingh, Raj Rup, Opt. Mater. 7 (1997) 33
[57] Ning Lei, Bing Xu, Zhonghong Jiang, Opt. Commun. 127 (1996) 263
[58] G. Pozza, D. Ajo, M. Bettinelli, A. Speghini, M. Casarin, Solid State Commun. 97 (1996) 521
[59] Y.C. Ratnakaram, S. Buddudu, Solid State Commun. 97 (1996) 651
[60] S. Sen, J.F. Stebbins, J. Non-Cryst. Solids 188 (1995) 54
[61] H. Ebendorff-Heidepriem, W. Seeber, D. Ehrt, J. Non-Cryst. Solids 183 (1995) 191
[62] K.J. Rao, Structural Chemistry of Glasses, Elsevier, Amsterdam, 2002
[63] D. Muller, G. Berger, I. Grunze, G. Ladwig, E. Hallas, and U. Haubenreisser, Phys.
Chem. Glasses 24 (1983) 37
[64] M. Schmucker and H. Schneider, J. Non-Crsyt. Solids, 311 (2002) 211
[65] T. Srikumar, M.G. Brik, Ch. Srinivasa Rao, Y. Gandhi, D. Krishna Rao, V. Ravi Kumar and N. Veeraiah, Spectrochim. Acta A, 81 (2011) 498
[66] C. Görller-Walrand, K. Binnemans, Handbook on the Physics and Chemistry of
Rare Earths, Elsevier, Amsterdam, 1998
[67] W. T. Carnall, G. L. Goodman, K. Rajnak, and R. S. Rana, J. Chem. Phys. 90 (1989) 3443
[68] K.S. Zou, H.T. Guo, M. Lu, W.N. Li, C.Q. Hou, W. Wei, J.F. He, B. Peng, X.L. Bin, Opt. Exp. 17 (2009) 10001
[69] T. Izumitani, H. Toratani and H. Kuroda, J. Non-Cryst. Solids, 47 (1982) 87
[70] M. Nakamura, Y. Mochizuki, K. Usami, Y. Itoh and T. Nozaki, Solid State
Commun. 50 (1984) 1079
[71] F. Moreau, A. Duran and F. Munoz, J. Eur. Ceram. Soc. 29 (2009) 1895
101
[72] P.F. McMillan, A. Grzechnik, H. Chotalla, J. Non-Cryst. Solids 226 (1998) 239
[73] J. Schwarz, H. Tichá, L. Tichý, R. Mertens, J. Optoelectronics Adv. Mater. 6 (2004) 737
[74] Y. Qiao, N. Da, D. Chen, Q. Zhou, J. Qiu, T. Akai, Appl. Phys. B 87 (2007) 717