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3 Chapter 3
Chapter 3
Lasing characteristics of
PbO-Sb2O3-B2O3:Nd2O3 glasses
87
3.1 Introduction:
The laser materials doped with Nd3+ ions [1] have become the hotspot because
Nd3+ ion has large absorption coefficient, wide absorption band, long fluorescence
lifetime, very large fluorescence branching ratio, energy compaction and the possibility
of lasing at different wavelengths at room temperature. They are the most investigated
lanthanide ions, not only due to its NIR emission, but also because of its sensitivity to a
changing crystal field can be used to extrapolate the spectral properties of other Ln ions
in a similar matrices [2]. On the other hand, the study of ion-ion interaction in highly
concentrated Nd3+ doped materials is a matter of both practical and theoretical
importance. High Ln concentration allows reducing the size of the gain media and/or
the pump power required. However, due to inherent disorder of glasses, ions in a nearby
sites may have different physical environment with greatly varying properties and, as a
consequence, special migration of energy and spectral diffusion within the in-
homogeneously broadened spectral profile [3] can occur. It is worthy noticing that the
migration of the electron excitation over the inhomogeneous profile (spectral migration)
and the wavelength dependence of the laser emission under narrow spectral site-
selective pumping.
Nd3+ ion is 4f3 ion with 4I9/2 ground state. The absorption and emission of this
ion has been reported in a number of glasses and crystalline materials because of its
potential applications in laser technology [4-5]. The transition 4I9/2→2P1/2 of Nd3+ ion in
absorption spectra is characteristic of coordination of this ion. Generally it is a strong
band and is desirable in the construction of compact and efficient laser source pumped
by diode laser. The effective coordination of this ion is found to be varying between 6
and 9 with the variation in the transition energy 23,300 cm-1 to 23,400 cm-1 [6]. The J-O
theory works very well for this ion and radiative parameters can therefore be
conveniently evaluated from J-O parameters.
88
3.2 Brief review of previous work done on neodymium doped glasses
Kam and Buddudu [1] have studied luminescence enhancement on Nd3+ and
Ce3+ doped SiO2; Al2O3 sol gel glasses. Wilhelm et al. [7] have reported the
fluorescence life time enhancement of Nd3+ sol-gel glasses by Al codoped ping and
Co2 laser processing. Karthikeyan and Mohan [8] have reported the structural, optical
and glass transition studies on Nd3+ doped lead borate glasses. Sen et al. [9] have
studied spectroscopic properties of Nd3+ doped transparent oxyfluoride glass ceramics.
Annapurna et al. [10] have investigated the NIR emission and up conversion
luminescence spectra of Nd3+: Zno-SiO2-B2O3 glasses. Shen et al. [11] have reported
the compositional effects and spectroscopy of rare earth (Er3+, Tm3+ and Nd3+) in
tellurite glasses. Kumar et al. [12] have explored the stimulated emission and radiative
properties of Nd3+ ions in barium fluorophosphates glass containing sulfate. Chen et al.
[13] have studied ion-implanted waveguides in Nd3+ silicate glasses and Er3+/Tb3+ co
doped phosphate glass. Saisudha and Ramakrishna [14] have found large radiative
transitions probabilities in bismuth borate glasses doped with Nd3+ ions. Rosa-Cruz et
al. [15] have reported the results of their study on spectroscopic characterization of
Nd3+ ions on barium phosphate glasses. Fernandez et al. [16-17] have evaluated the
upconversion losses in Nd3+ doped fluoro arsenate glasses. Surana et al. [18] have
investigated the laser action in neodymium doped zinc chloride boro phosphate
glasses. Vijaya Praksh reported [19] his results of absorption studies of Pr, Nd, Sm,
Dy, Ho and Er ions in NASICON type phosphate glasses Na4 AlZnP3O12. Rao et al.
[20] have reported luminescence properties of Nd3+: emission in violet from yellow in
Nd3+ : SiO2-TiO2-Al2O3 sol-gel glasses. Bouderbala et al. [21] have reported the results
of their studies in infrared and visible room temperature florescence induced by
continuous laser excitation of new Nd3+: phosphate glasses. Cassanjes et al. [22] have
investigated Raman scattering, differential scanning calorimetry and Nd3+ spectroscopy
in alkali niobium tellurite glasses. Mehta et al. [23-24] have investigated the
spectroscopic properties including ESR of Nd3+ doped phosphate and borate glasses.
Kumar and Bhatnagar [25] have reported the effect of the modifier ions on the
covalence of Nd3+ ions in cadmium borate glasses. Srinivas rao et al. [26] have
89
reported the physical and absorption properties of Nd3+ doped mixed alkali fluoro-
borophosphate optical glasses. Ajit kumat et al. [27] have reported the spectroscopic
parameters of Nd3+ ions in phosphate glasses. Joshi and Lohani [28] have investigated
the non radiative energy transfer from Tm3+ to Ho3+ and Nd3+ in zinc phosphate glass.
Dewar et al. [29] have studied the optical and acousto-optical properties of Nd:
phosphate glasses. Ning et al. [30] have fabricated Ti: sapphire laser pumped Nd:
tellurite glass laser. Pozza et al. [31] have investigated the absorption and
luminescence spectroscopy of Nd3+ and Er3+ in zinc borate glass. Ratnakaran and
Buddudu [32] have reported the optical absorption spectra and laser analysis of Nd3+
ions in fluoroborate glasses. Sen and Stebbains [33] have studied structural role of
Nd3+ in SiO2 glass using NMR studies. Ebendorff et al. [34] have studied the
spectroscopic properties of Nd3+ ions in Phosphate glasses.
3.3 Sample preparation
The molar composition of the glasses under study is 30 PbO-25 Sb2O3-(45-x)
B2O3 –x Nd2O3 where x= 0, 0.2, 0.4, 0.6 and 1 .The samples were labeled as N0, N2,
N4, N6, N8 and N10 respectively. Appropriate amounts of AR grade reagents of PbO,
Sb2O3, B2O3, and Nd2O3 powders are thoroughly mixed in agate mortar and melted in a
silica crucible in the temperature range of 900 to 950 °C in a programmable electrical
furnace for thirty minutes until bubble free liquid is formed. The resultant melt is
poured in a brass mold and subsequently annealed at 250 °C for 2 h. The samples
prepared were then ground and optical polished to the dimensions of 1 cm × 1 cm × 0.2
cm. The detailed composition of the samples is
N0: 30 PbO-25 Sb2O3-45 B2O3-0 Nd2O3
N2: 30 PbO-25 Sb2O3-44.8 B2O3-0.2 Nd2O3
N4: 30 PbO-25 Sb2O3-44.6 B2O3-0.4 Nd2O3
N6: 30 PbO-25 Sb2O3-44.4 B2O3-0.6 Nd2O3
N8: 30 PbO-25 Sb2O3-44.2 B2O3-0.4 Nd2O3
N10: 30 PbO-25 Sb2O3-44 B2O3-1.0 Nd2O3
90
3.4 Physical parameters
Various physical properties like density, molar volume, oxygen mol%, oxygen
packing density, Nd3+ ion concentration, inter ionic distance, refractive index, polaran
radius, molar refraction and polarizability of Nd3+ doped glasses are calculated and
presented in Table 3.1.
As the concentration of Nd3+ ions increased, a considerable increase in the
density or a considerable decrease in the molar volume of samples is observed.
Modification of the geometrical configurations of the glass network, change in
coordination and the variation of dimensions of the interstitial holes can be considered
as responsible for such a variation of density. Oxygen packing density is also found to
increase with the increase in the concentration of Nd3+ ions. Such an increase indicates
an increase in the structural compactness of the samples.
3.5 Characterization
3.5.1 XRD
The X-ray difractograms are important to know the amorphous nature of the
sample. The X-ray diffraction of all the samples were recorded on Rigaku
diffractometer mini flex with CuKɑ radiation. The absence of sharp peaks in the X-ray
diffraction (Fig. 3.1 ) pattern indicates the amorphous (glass) nature of the samples.
3.5.2 Differential scanning calorimetry
The glass transition temperatures of these glasses were determined by differential
scanning calorimtry traces that were recorded using DSC Q20 (TA-Instruments) with a
programmed heating rate of 20 oC per minute in the temperature range 50-500oC and
presented in the figure Fig. 3.2. All DSC traces indicate typical glass transitions with
the inflection points between 380 oC to 390 oC. Although the inflection points of all the
samples appear to be nearly same, it is interesting that the glass transition temperature
shows increasing trend with increase in dopant concentration. The glass transition
temperature for all the samples were presented in the Table 3.2.
Table 3.1 Physical parameters of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.
Glass
Physical Parameter N0 N2 N4 N6 N8 N10
1 Average MW(g/mol) 171.16 171.7 172.23 172.76 173.3 173.83
2 Density, ρ (g/cc) (±0.001) 4.972 5.101 5.212 5.316 5.481 5.567
3 Refractive index, n (±0.001) 1.503 1.512 1.517 1.521 1.524 1.529
4 Molar Volume, Vm (MW/ρ) (±0.01) 31.99 33.93 33.41 32.62 32.06 31.31
5 Molar Refraction, RM (±0.001) 9.457 10.181 10.108 9.933 9.809 9.656
6 Polarizability, αe
(×10-24cm3) (±0.001) 3.75 4.034 4.005 3.936 3.886 3.826
7 Oxygen mol % , O (±0.01) 2.4 2.4 2.4 2.4 2.4 2.4
8 Oxygen packing density (gm atom/L) (±0.01) 75.02 70.73 71.83 73.57 74.86 76.65
9 Nd3+ ion concentration, Ni (×1021/cc)(±0.01) 0 0.11 0.22 0.33 0.45 0.58
10 Inter ionic distance, ri (Å) (±0.001) - 20.87 16.57 14.47 13.05 11.99
11 Polaran radius, rp (Å ) (±0.001) - 0.146 0.158 0.165 0.171 0.176
Fig. 3.1 X- ray difractograms of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.
Fig. 3.2. Variation of glass transition temperature of PbO-Sb2O3-B2O3 glasses with
increasing in Nd3+ ion concentration.
-0.8
-0.6
-0.4
-0.2
060 110 160 210 260 310 360 410 460
Hea
t flo
w (
W/g
m)
Temperature
N2
N4
N6
N8
N10
93
Table 3.2 Thermal parameters of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.
Name of the sample Glass Transition Temperature (C) (±1)
N2 384
N4 385
N6 387
N8 391
N10 392
3.5.3 FTIR spectra
Fourier transform infrared spectra of Nd3+ doped PbO-Sb2O3-B2O3 glasses is
shown in the Fig. 3.3. The infrared transmission spectra of PbO-Sb2O3-B2O3 :Nd2O3
glasses exhibited bands originated from borate groups at 1200 cm-1 to 1400cm-1 due
to asymmetric stretching of trigonal BO3 units, 1050 cm-1 due to stretching of
tetrahedral BO4 units and another band at 688 cm-1 due to bending of B-O-B
linkages in the borate network [35]. The 1 vibrational band of SbO3 units appeared
at 930 cm-1. The 3 vibrational bands of SbO3 units merged with the band due to
bending vibrations of B-O-B linkages and may have formed a common vibrational
band due to B-O-Sb linkages [36]. In addition, a band due to PbO4 structural groups
at about 462 cm-1 [37] is also observed for all the samples. The bands at 1750 cm-1
and 3000 cm-1 may be due to the stretching vibration of hydroxyl (OH) complexes,
which are due to the absorbed water molecules on the surface of the material.
Fig. 3.3 FTIR spectra of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ion.
400 800 1200 1600 2000 2400 2800 3200
Tra
ansm
itta
nce(
%)
Wavenumber (cm-1)
BO3 Units
B-O-B linkage
PbO4 Units ν1-Sb2O3 Units
BO4 Units
N0
N2
N4
N6
N8
N10
OH Units
OH Units
95
3.6 Optical absorption
The optical absorption spectra (Fig. 3.4) of Nd3+ doped PbO-Sb2O3-B2O3 glasses was
recorded at room temperature in the spectral wavelength range covering 300–2000 nm
with a spectral resolution of 1 nm, have exhibited twelve well resolved bands with
respect to its ground state 4I9/2 at
4D5/2 (368nm)
2D5/2 +2P1/2 (433nm)
4G11/2 (463nm)
2K15/2+2D3/2+
2G9/2 (478nm)
4G9/2 (516 nm)
4G7/2 (527 nm)
4G5/2 + 2G7/2 (583 nm)
2H11/2 (632 nm)
4F9/2 (681 nm)
4F7/2 + 4S3/2 (747 nm)
4F5/2 + 2H9/2 (804 nm)
4F3/2 (877 nm)
The increase in the concentration of neodymium ions in the glass matrix does
not alter the spectral positions of the absorption bands significantly but the absorption
strengths under given peek is found to be increased.
3.6.1 Optical parameters
The optical band gap energy is calculated from the extrapolation of linear region
of graph (α ħω)1/2 against ħω and presented in the Fig. 3.5. Optical band gap energies of
the samples were decreasing with increasing the concentration of Nd3+ ions. Urbach
plots are obtained by plotting ln(α) against ħω. The values of Urbach energy (ΔE) are
calculated by determining the reciprocals of the slopes of linear region of curve.
Fig. 3.4 Optical absorption spectra of PbO−Sb2O3−B2O3 glasses doped with Nd3+ recorded at room temperature. All
transitions are from the ground state 4I9/2.
350 450 550 650 750 850
Abs
orba
nce
(a.u
)
Wavelength (nm)
N0
N2
N4
N6
N8
N10
4F3/2
4F5/2+2H9/2
4F7/2+4S3/2
4F9/22H11/2
4G5/2+2G7/2
4G7/24G9/2
2K15/2 +2D3/2+2G9/2
4G11/2
2D5/2+2P1/2
4I9/2
4D5/2
Fig. 3.5 Tauc plots for evaluation of optical band gap energy of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
3.3 3.32 3.34 3.36 3.38 3.4 3.42 3.44 3.46
(αhυ
)1/2cm
-1/2
eV1/
2
hυ (eV)
N0
N2
N4
N6
N8
N10
98
The Urbach energy indicates the degree of disorder i.e. higher is the Urbach
energy, higher is the disorder. It is observed that the Urbach energy of all the samples is
increasing with increase in the concentration of Nd3+ ions. Similarly cut of wavelengths
are calculated for all the samples which are observed to be shifting towards lower
wavelength with increase in the concentration of Nd3+ ions. Table 3.3 shows the optical
parameters of PbO-Sb2O3-B2O3 doped with Nd3+ ions.
Table 3.3 Optical parameters of Nd3+ doped lead antimony borate glasses.
GlassPhysical Parameter N0 N2 N4 N6 N8 N10
1 Cutoff wavelength, λ (nm)(±1)
353 355 356 357 359 361
2 Optical bandgap energy, Eopt
(eV) (±0.001)3.399 3.391 3.386 3.383 3.38 3.374
3 Urbach Energy, ΔE (eV)(±0.001)
0.511 0.523 0.529 0.538 0.551 0.563
3.6.2 Oscillator strengths
The intensities of absorption transitions of optical absorptions are measured in
terms of oscillator strengths (fexp) and determined from the relative areas under the
absorption bands. The experimental oscillator strengths (fexp) and calculated oscillator
strengths are computed by using the equations 1.9 and 1.23 respectively and presented
in Table 3.4. The small value of root mean square (rms) deviations between
experimental and calculated oscillator strengths indicated good agreement between
them.
Table 3.4 The experimental (fexp x10-6) and calculated (fcal x10-6) spectral intensities of Nd3+ doped antimony lead borate
glasses. All the transitions are from its ground state 4I9/2.
Transitions fromground state 4I9/2
N2 N4 N6 N8 N10
f exp f cal f exp f cal f exp f cal f exp f cal f exp f cal
4F3/2 2.3 2.12 2.34 2.4 2.44 2.4 2.67 2.61 2.73 2.72
4F5/2 + 2H9/2 7.01 6.66 7.28 7.46 7.7 7.46 8.44 8.07 8.82 8.31
4F7/2 + 4S3/2 9.1 9.3 9.6 10.35 10.22 10.35 11.21 11.17 11.14 11.45
4F9/2 0.38 0.69 0.58 0.77 0.63 0.77 0.69 0.83 0.73 0.85
2H11/2 0.13 0.19 0.14 0.21 0.15 0.21 0.17 0.23 0.19 0.24
4G5/2 + 2G7/2 21.29 21.3 22.77 24.14 24.14 24.14 26.33 26.33 26.71 26.71
4G7/2 3.8 3.49 3.88 3.95 4 3.95 4.43 4.3 4.45 4.42
4G9/2 0.67 0.7 0.68 0.78 0.77 0.78 0.86 0.84 1.13 0.86
2k15/2+2D3/2+
2G9/2 0.76 0.76 1.17 1.17 1.27 1.38 1.38 1.38 1.46 1.46
4G11/2 0.84 0.98 0.86 1.1 0.98 1.1 1.09 1.2 1.07 1.24
2P1/2+2D5/2 0.47 0.47 0.72 0.54 0.94 0.54 0.97 0.59 1 0.61
4D5/2 3.92 5.1 4.67 5.79 5.21 5.79 5.41 6.31 5.56 6.56
RMS Deviation 0.4 0.6 0.24 0.32 0.39
100
3.6.3 Judd-Ofelt parameters
Judd-Ofelt theory has been used to investigate radiative nature of trivalent rare
earth ions in a variety of laser host materials [38-39]. The calculated oscillator strengths
fcal were determined by using the Judd-Ofelt theory. Judd–Ofelt intensity parameters Ωλ
for these glasses were evaluated with the usual procedure i.e. by performing least square
fit analysis between the experimental oscillator strengths( fexp) , theoretical oscillator
strengths (fcal), the wave numbers (cm-1) and doubly reduced matrix elements U(λ)2
with λ = 2, 4, 6.
The computed data of U(λ)2 for different absorption states of rare earth ions
[40] and also for different emission levels is available in literature. According to the
literature [41-45], the unit tensor operator will not significantly change their values
depending on host charge around the dopant rare-earth ions in host material. Therefore
the literature data have been used in the parameterization of absorption and
photoluminescence spectra of the Nd3+ glasses studied and presented in the Table 3.5.
The positions and the spectral intensities of certain transitions of rare earth ions
are very sensitive to the environment of the rare earth ions [46]. These transitions
follows selection rules such as [47-48] ΔJ ≤ 2, ΔL ≤ 2 and ΔS = 0, called as hyper
sensitive transitions. From Fig. 3.4, it is noticeable that the transition 4I9/2 →4G5/2 + 2G7/2
at about 583 nm is much brighter than the other transitions and is a hyper sensitive
transition. The hyper sensitive transitions (bands) are normally associated with the
larger values of U22 and hence intimately related to Ω2.The intensity parameter Ω2
indicates the covalency of the rare earth ligand bond and increases with increase in the
intensity of the hyper sensitive transition [49]. The same tendency is observed for the
present glass system.
The Judd-Oflet parameters of all the samples were calculated and presented in
Table 3.6. The intensity parameter Ω2 is associated with the symmetry of ligand field
around rare earth ion and hence the covalency of rare earth ion. For the present study,
Ω2 follows the order N10 > N8 > N6 > N4 > N2. This trend indicates that the symmetry
of the site associated with Nd3+ ion is highest for N2 glasses and lowest for N10 glasses.
Table 3.5 Energy level assignments and matrix elements of U(λ)2 for Nd3+ ions
S.No Transition Wave length λ (nm) wavenumber (cm-1) U22 U42 U62
1 4F3/2 877 11402 0 0.23 0.0571
2 4F5/2 + 2H9/2 804 12437 0.0005 0.2314 0.4001
3 4F7/2 + 4S3/2 747 13386 0.0009 0.0448 0.6583
4 4F9/2 681 14684 0.0009 0.0094 0.0402
5 2H11/2 632 15822 0.0006 0.0026 0.01
6 4G5/2 + 2G7/2 583 17152 0.9753 0.5995 0.0859
7 4G7/2 527 18975 0.0536 0.1557 0.0515
8 4G9/2 516 19379 0.0066 0.0002 0.0298
9 2k15/2+2D3/2+
2G9/2 478 20920 0.0000 0.0052 0.0143
10 4G11/2 463 21598 0.001 0.0404 0.0216
11 2P1/2+2D5/2 433 23094 0.0000 0.0366 0.0000
12 4D5/2 368 27173 0.0001 0.2542 0.0457
102
Table 3.6 Judd - Ofelt Ωλ×1020 (cm2) parameters of Nd3+ doped lead antimony borate
glasses along with trends of a number of other glass systems containing Nd3+ ions.
Glass Ω2 Ω4 Ω6 Trend Reference
N2 5.72 3.77 6.89 Ω6>Ω2>Ω4 Present work
N4 6.12 4.032 7.22 Ω6>Ω2>Ω4 Present work
N6 6.46 4.31 7.66 Ω6>Ω2>Ω4 Present work
N8 7.01 4.68 8.22 Ω6>Ω2>Ω4 Present work
N10 7.02 4.89 8.41 Ω6>Ω2>Ω4 Present work
PKMAN10 6.22 5.95 6.83 Ω6>Ω2>Ω4 [50]
K2O-PbO-B2O3 5.90 5.71 6.21 Ω6>Ω2>Ω4 [51]
30Li2O-70B2O3 4.20 3.89 4.74 Ω6>Ω2>Ω4 [52]
3Nd2O3-97[30PbO-70B2O3] 3.96 3.77 4.88 Ω6>Ω2>Ω4 [14]
3Nd2O3-97[40PbO-60B2O3] 3.59 3.50 5.62 Ω6>Ω2>Ω4 [14]
3Nd2O3-97[50PbO-50B2O3] 3.59 3.02 5.32 Ω6>Ω2>Ω4 [14]
3Nd2O3-97[60PbO-40B2O3] 3.61 3.02 5.34 Ω6>Ω2>Ω4 [14]
3Nd2O3-97[70PbO-30B2O3] 3.52 2.98 5.48 Ω6>Ω2>Ω4 [14]
LiCdBs 34.51 10.17 36.89 Ω6>Ω2>Ω4 [53]
NaCdBs 21.06 20.85 27.99 Ω6>Ω2>Ω4 [53]
Vitreous borate 4.30 3.60 4.70 Ω6>Ω2>Ω4 [54]
10Na2O-90B2O3 3.40 2.90 4.30 Ω6>Ω2>Ω4 [55]
PKBAFN(2) 6.60 6.36 7.30 Ω6>Ω2>Ω4 [56]
30CaO-70B2O3 4.4 3.7 4.6 Ω6>Ω2>Ω4 [57]
SBBI 4.72 2.12 3.93 Ω2 >Ω6>Ω4 [58]
SBBI 4.81 1.97 3.94 Ω2 >Ω6>Ω4 [58]
103
3.6.4 Radiative properties
Various radiative parameters such as electric dipole line strength (Sed), magnetic
dipole line strength (Smd), radiative transition probability (AR), total radiative transition
probabilities(AT), the radiative decay times (τR), and branching ratio(βR) of Nd3+ doped
lead antimony borate glasses were calculated using the equations
1.14,1.15,1.25,1.26,1.27 and 1.29 respectively. The radiative parameters of lead
antimony borate glasses for 1% of Nd3+ are presented the Table 3.7.
The values of the branching ratios βR for the 4F3/2 → 4IJ ( J=15/2, 13/2, 11/2 and
9/2) transition depends upon the Ω4/Ω6 since Ω2 does not contribute in determining the
intensity of these bands as U22 is zero for these transitions. In lead antimony borate
glasses, approximately 35% of transition terminates at the 4I9/2 state, 53% at 4I11/2 state,
11% at 4I13/2 state and 5% radiate to the 4I15/2 states.
104
Table 3.7 Electric dipole line strength (Sed), magnetic dipole line strength (Smd),radiative transition probability (AR) branching ratio(βR) , the total radiative transitionprobabilities(AT) and radiative decay times (τR) of Nd3+ doped lead antimony borateglasses.
InitialІ(S,L)J>
FinalІ(S',L')J>
wave number(cm-1)
Sed x1022
(cm2)Smd x1022
(cm2)A (s-1) βR %
4G9/24G7/2 483 204.31 16.72 0.06 02G7/2 2319 125.59 34.52 4.74 0.034G5/2 2408 258.2 0 8.34 0.052H11/2 3607 200.49 0.06 21.78 0.144F9/2 4890 199.56 3.27 54.99 0.354S3/2 6036 98.32 0 50.03 0.324F7/2 6126 479.5 0.21 255.22 1.63
2H9/2 7030 127.66 0.49 103.08 0.664F5/2 7078 189.68 0 155.64 0.994F3/2 8102 150.81 0 185.6 1.184I15/2 13626 272.15 0 1593.29 10.164I13/2 15690 894.2 0 7992.49 50.944I11/2 17672 320.69 0.04 4096.14 26.114I9/2 19531 67.7 0.01 1167.36 7.44
∑A (s-1)= 15688 τR (μs)= 63
4G7/22G7/2 1836 27.31 0.67 0.5 04G5/2 1925 144.39 27.19 3.61 0.032H11/2 3124 117.45 0 10.36 0.084F9/2 4407 14.79 0.02 3.67 0.034S3/2 5553 93.67 0 46.39 0.364F7/2 5643 147.81 1.1 77.47 0.6
2H9/2 6547 399.39 0 324.2 2.534F5/2 6595 256.17 0.7 213.19 1.664F3/2 7619 98.23 0 125.67 0.984I15/2 13143 15.78 0 103.64 0.814I13/2 15207 156.39 0 1590.89 12.414I11/2 17189 487.87 0 7167.14 55.934I9/2 19048 157.45 0 3147.53 24.56
∑A (s-1)= 12814 τR (μs)= 78
105
InitialІ(S,L)J>
FinalІ(S',L')J>
wave number(cm-1)
Sed x1022
(cm2)Smd x1022
(cm2)A (s-1) βR
4G5/24F9/2 2482 116.96 0 6.9 0.034S3/2 3628 88.1 0 16.23 0.084F7/2 3718 217.72 0.13 43.19 0.21
2H9/2 4622 10.91 0 4.16 0.024F5/2 4670 250.43 0.02 98.38 0.474F3/2 5694 364.55 0.03 259.58 1.254I15/2 11218 3.7 0 20.16 0.14I13/2 13282 57.02 0 515.28 2.494I11/2 15264 221.81 0 3042.42 14.684I9/2 17123 863.39 0 16717.54 80.67
∑A (s-1)= 48 τR (μs)= 20833
2H11/24F9/2 1283 92.78 4.1 0.4 0.094S3/2 2429 28.1 0 0.78 0.174F7/2 2519 129.37 0 3.99 0.88
2H9/2 3423 250.83 15.23 20.72 4.574F5/2 3471 21.03 0 1.7 0.374F3/2 4495 7.2 0 1.26 0.284I15/2 10019 118.32 0 229.47 50.614I13/2 12083 13.01 0.93 47.79 10.544I11/2 14065 12.49 0.26 68.59 15.134I9/2 15924 10.11 0 78.73 17.36
∑A (s-1)= 453 τR (μs)= 2205
4F9/24S3/2 1146 2.05 0 0.01 04F7/2 1236 140.32 28.68 0.75 0
2H9/2 2140 38.43 19.22 1.36 04F5/2 2188 124.08 0 3.01 04F3/2 3212 100.8 0 7.73 04I15/2 8736 657.82 0 1014.9 0.224I13/2 10800 553.08 0 1612.27 0.354I11/2 12782 331.65 0.16 1603.57 0.354I9/2 14641 43.39 0.11 316.03 0.07
∑A (s-1)= 4559 τR (μs)= 219
106
InitialІ(S,L)J>
FinalІ(S',L')J>
wave number(cm-1)
Sed x1022
(cm2)Smd x1022
(cm2)A (s-1) βR
4F5/24F3/2 1024 81.89 34.02 0.5 0.014I15/2 6548 194.09 0 210.17 4.094I13/2 8612 427.41 0 1052.89 20.494I11/2 10594 112.26 0 514.81 10.024I9/2 12453 451.22 0 3360.75 65.4
∑A (s-1)= 5139 τR (μs)= 194
4F3/24I15/2 5524 22.89 0 22.33 0.574I13/2 7588 177.93 0 449.73 11.434I11/2 9570 411.22 0 2085.1 53.014I9/2 11429 159.39 0 1376.6 34.99
∑A (s-1)= 3934 τR (μs)= 254
3.7 Photoluminescence
The fluorescence spectra of Nd3+ in the wavelength range 800nm to 1500 nm
recorded with an excitation wavelength of 808 nm and was shown in the Fig. 3.6. The
spectra shows a broad band at 898 nm, a strong band at 1058 nm and another band at
1328 nm. These bands are identified as
4F3/2→4I9/2 (898 nm)
4F3/2→4I11/2(1056 nm)
4F3/2→4I13/2(1328 nm)
respectively. The intensity of the bands is observed to be increasing with concentration
of Nd3+ ions, but no considerable shift in the position is observed.
Fig. 3.6 Normalized emission spectra of PbO - Sb2O3 - B2O3 glasses doped with Nd3+ ions recorded at room temperature(λexc=808 nm).
0
0.2
0.4
0.6
0.8
1
800 900 1000 1100 1200 1300 1400
Nor
mal
ized
inte
nsit
y (A
.U.)
Wavelength (nm)
N2
N4
N6
N8
N10
4F3/2 →4I11/2
4F3/2 →4I9/2
4F3/2 →4I13/2
3.7.1 Stimulated emission cross section
An efficient laser transition is characterized by a large stimulated emission
cross section while the induced emission cross sections are characterized by Judd-
Ofelt theory. The stimulated emission cross-section is given by Fuchtbabauer-
Ladenburg method [59]
),(8 2
4
JJAcn T
eff
p
3.1
where λP is the peak wavelength, Δλeff is the effective bandwidth of the emission
band, n is the refractive index of the sample and AT(ψJ,ψʹJʹ) is the total spontaneous
emission probability. The effective band width and emission cross- section values
are presented in the Table 3.8.
Table 3.8 Emission cross sections of Nd3+ doped lead antimony borate glasses for
the transitions 4F3/2 →4 I J ( J=13/2, 11/2,9/2).
Transition λP Δλeff σe (x10-20) cm2
4F3/2→ N2 N4 N6 N8 N10 N2 N4 N6 N8 N10
4I13/2 1329 29 30 31 33 34 2.22 2.26 2.32 2.35 2.34
4I11/2 1059 25 26 27 28 29 4.77 4.84 4.96 5.07 5.13
4I9/2 896 48 49 50 53 54 0.81 0.85 0.89 0.91 0.93
Fig 3.7 shows a partial energy diagram of the excited manifolds of Nd3+ ions
and several relevant transitions corresponding to the excited 4F3/2 state absorption
and emission. The three excited state absorption transitions correspond to the three
laser levels at 1.35 μm, 1.06 μm and 0.88 μm. The energy level separations between
the 4F3/2 and the upper 4G7/2,2G9/2 and 2P1/2 levels are in all cases close enough to the
energies of possible laser transitions from the 4F3/2 level to lower terminal levels4I13/2,
4I11/2 and 4I9/2, respectively. But among the three transitions from 4F3/2 , the
transition 4F3/2 → 4I11/2 will be a potential lasing transition because of its higher
stimulated emission cross- section (5.13×10-20 cm2) and higher branching ratio (53
%). An electric dipole transition between 4F3/2 and 2G9/2 level near 1.06 μm could
109
reduce the net cross-section for stimulated emission between4F3/2 and 4I11/2 level as
absorbed by Vance .
Fig. 3.7 Energy level diagram of Nd3+ doped lead antimony borate glasses.
3.7.2 Decay curves
The Fig 3.8. shows the decay profile of the 4F3/2→4I11/2 transition of Nd3+
doped lead antimony borate glasses excited at 808 nm wavelength recorded at room
temperature. The experimental life times along with the branching ratios and
emission cross-sections of all the glasses are presented in the Table 3.9
When the Nd3+ ion is excited from its ground state to the levels having energy
higher than that of 4F3/2, they decay non-radiatively to lower levels down to the 4F3/2
state due to very small energy gaps between the adjacent energy levels. As the
energy gap between the metastable 4F3/2 level and its lower level 4I13/2 is sufficiently
large (5600 cm−1 approximately), radiative transitions will predominate here over
the non-radiative transitions state depends upon the values of J-O parameters,
especially on Ω4 and Ω6 , as well as on the host refractive index. It represents a mean
110
value over the different sites occupied by the Nd3+ ions in the glass matrix and it is
higher than that determined experimentally from the luminescence decay. This
reduction in experimental lifetime can be explained by considering all the possible
relaxation processes relative to the excited Nd3+ ions. If the experimentally
measured lifetime of the emitting state is denoted by τ, then the total decay rate (1/τ)
is the sum of radiative (Ar ) and non-radiative(Wn−r ) decay rates. Therefore,
rnr WA 1
3.2
In glasses, principally, there are four non-radiative processes contributing to
the reduction of measured lifetime of the emitting level.
W n−r = Wm−p + W c−q + W e−t + WOH 3.3
where Wm−p, Wc−q, We−t and WOH denotes the non-radiative decay rates
corresponding to the multi phonon relaxation process, concentration quenching,
energy transfer to another doping impurity and hydroxyl (OH−) groups, respectively.
Wm−p decreases exponentially as the energy gap between the neighboring energy
levels increases [60-61]. For the Nd3+ ion, the energy gap between the 4F3/2 level and
its lower level 4I15/2 is sufficiently large enough that Wm−p is negligible compared to
the radiative decay rate of the 4F3/2 level of the Nd3+ ion in lead antimony borate
glasses. For weak concentrations, the non-radiative relaxations due to ion–ion
interactions (Wc−q and We−t) will be almost negligible and the radiative lifetime will
be in agreement with that of experimental values.
In the present glass systems the lifetime is decreased with increase in
concentration of acceptors (Nd3+ ions). The decay curves of the glasses are found to
be varying from exponential to non-exponential and this non- exponential nature
increases with increase of Nd3+ ion concentration due to enhanced energy transfer by
cross-relaxation between two Nd3+ ions [62]. This is also clearly evident from the
decreased lifetimes of the 4F3/2 level in Nd3+ lead antimony borate glasses decreased
from 328 µs to 254 µs 0.2 to 1.0 mol%. The non-exponential nature of the decay
curves is well fitted to the Inokuti–Hirayama model for S=6, indicating that the
dominant interaction for energy transfer through cross-relaxation between Nd3+ ions
is of dipole–dipole type.
111
Fig 3.8. The radiative lifetime of the 4F3/2
Fig. 3.8. Luminescence decay profiles for the 4F3/2 →4F11/2 transition of Nd3+ doped
lead antimony borate glasses.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000 2500 3000
Nor
mal
ized
inte
nsit
y (a
rb.u
nits
)
Time (μs)
N2
N4
N6
N8
N10
112
Table 3.9. Experimental life times, branching ratios (β%), and emission cross
sections (σe) of Nd3+ ion in lead antimony borate glasses for 4F3/2→4F11/2.
Sample τexp (μs) β% σe (×10-20) cm2
N2 207 53.5 4.77
N4 201 53.4 4.84
N6 194 53.3 4.96
N8 184 53.2 5.07
N10 182 53.1 5.13
From the table the branching ratios of samples are almost constant but
however the emission cross-sections are increasing with the concentration of Nd3+
glasses. The N10 glass with more than 50% of branching ratio and higher emission
cross-section is suitable for efficient laser emission.
3.8 Conclusions
Lead antimony borate glasses with different concentrations of neodymium
were prepared by the conventional melt quenching method. The amorphous (glass)
nature was confirmed by the characterization technics such as X-ray difractograms
and DSC traces.
The various physical and parameter of the samples were calculated and
analysed. The density of the glasses is increasing with increase in the mol% of rare
earth ions almost linearly because; the high dense rare earth ions are replacing low
dense B2O3. In general the density and molar volume show opposite behaviour and
the same thing is reflected here. The molar volume of the glass samples is
decreasing with increase in the Nd3+ concentration. The oxygen packing density of
the samples increased with increase in the mol% of rare earth ions. Refractive index
of the samples also increased with increase in concentration whereas molar
refraction and polarizability are decreased.
Fourier transform infrared spectra PbO-Sb2O3-B2O3:Er2O3 glasses exhibited
five conventional bands at 1330 cm-1 (BO3 units), 1050 cm-1 (BO4 units), 688 cm-1
113
(bending vibrations of B-O-B linkages) , 930 cm-1 ( 1 vibrational band of SbO3)
and 462 cm-1 (PbO4 structural groups).
The optical absorption spectra of Er3+ doped lead antimony borate glasses
has exhibited twelve absorption bands. All the bands are identified according to
Carnall. Cut of wavelength is shifting to higher wavelength with increase in Nd3+ ion
concentration. The systematic spectroscopic analysis of neodymium doped lead
antimony borate glass systems has been performed using Judd-Ofelt theory. It has
been found that the Judd–Ofelt intensity parameters follows the trend Ω6>Ω2>Ω4.
The Judd- Ofelt parameters were increasing with Nd2O3 concentration and found to
be maximum for 1 mol% of Nd2O3 (N10).
The fluorescence spectra of Nd3+ shows a broad band at 898 nm, a strong
band at 1058 nm and another band at 1328 nm. The luminescence intensity of
various emission bands increased with the concentration of rare earth ions indicates
that there is no luminescence quenching in these glasses within the concentration
range studied. It has been found that the efficiency of all the transitions i.e.4F3/2→4I9/2 , 4F3/2 →4I11/2 and 4F3/2 →4I13/2 increases as the difference between Ω4 and
Ω6 increases with increasing Nd2O3concentration. In addition, it has been observed
that the emission cross-section for the 4F3/2 →4I11/2 transition is more than 4F3/2→4I9/2
and the 4F3/2 → 4I13/2 transitions for all the glasses. The branching ratio βR values for
the transition 4F3/2→4I11/2 (1.06μm) is about 53% with emission cross-section of
5.13×10-20 cm2. Hence, the transition 4F3/2→4I11/2 will be a potential lasing transition.
To maximize lasing transition fluorescence intensity, preferable condition is Ω6>Ω4
which is observed in Nd3+ doped lead antimony borate glasses.
114
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