Y. Gandhi

Influence of aluminum ions on fluorescent spectra and upconversion in codoped CaF2–Al2O3–P2O5–SiO2:Ho3+ and Er3+ glass system

The glasses of the composition 20CaF2–xAl2O3–(59−x)P2O5–20SiO2:1.0Ho2O3/1.0Er2O3 and 20CaF2–xAl2O3–(59−x)P2O5–20SiO2:(0.6Ho2O3+0.4Er2O3) with x varying from 2 to 10 mol % have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350–2100 nm were studied at ambient temperature. The Judd–Ofelt theory was applied to characterize the absorption and luminescence spectra of Ho3+ and Er3+ ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio β, and the radiative life time τ for blue (B), green (G), and red (R) emission levels of these glasses have been evaluated. The radiative life times for these transitions of Ho3+ and Er3+ have also been measured. The variations observed in these parameters were discussed in the light of varying coordinations (tetrahedral and octahedral positions) of Al3+ ions in the glass network. The energy transfer between the two rare earth ions (Ho3+ and Er3+) in codoped CaF2–...

Dielectric and spectroscopic investigations of lithium aluminium zirconium silicate glasses mixed with TiO2

Li2O–Al2O3–ZrO2–SiO2 glasses mixed with different concentrations of TiO2 (ranging from 0 to 5.0 mol%) were synthesised and their dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) investigated over wide ranges of frequency and temperature. Studies of optical absorption, ESR, infrared (IR) and photoluminescence properties have also been undertaken. A decrease in dielectric parameters with increasing concentrations of TiO2 has been observed and this is attributed to an increasing proportion of titanium ions occupying network-forming positions rather than going into interstitial positions. A.C. conductivity in the high-temperature region appears to be connected both to electronic transfer and ionic movements, but conduction attributed to such processes seems to be hampered by the entry of titanium ions into the network-forming positions. Analysis of the results of the IR spectral studies have indicated that there is a decreasing degree of disorder in the glass network with increasing TiO2 content. The optical absorption and ESR spectral studies have revealed that titanium ions exist in both Ti3+ and Ti4+ states in the glasses. Luminescence spectra exhibited an emission band in the visible region and the luminescence efficiency increased with TiO2 content. The excitation of substitutionally positioned octahedral Ti4+ ions is identified as being responsible for the observed luminescence emission.

Electrical, dielectric and spectroscopic studies on MnO doped LiI–AgI–B2O3 glasses

LiI–AgI–B2O3 glasses doped with different concentrations of MnO (ranging from 0 to 0.8 mol%) were prepared. Electrical and dielectric properties have been studied over a wide frequency range of 10−2 – 106 Hz and in the temperature range from 173 to 523 K. The valence states of manganese ions and their coordination in the glass network have been investigated using optical absorption, luminescence, and ESR spectroscopy. The analysis of the spectroscopic results has indicated that the manganese ions exist in both Mn2+ and Mn3+ states and occupy octahedral and tetrahedral positions. With increasing MnO concentration there is a gradual increase in the tetrahedral occupancy of Mn2+ ions at the expense of octahedral occupancy in the glass network. The results of dc conductivity have indicated that when T > θD/2, the small polaron hopping model is appropriate and the conduction is adiabatic in the nature. Further, the analysis of experimental data indicates that there is a mixed, ionic and electronic, conduction....

Role of modifier oxide in emission spectra and kinetics of Er–Ho codoped Na2SO4–MO–P2O5 glasses

The glasses of the composition 19Na(2)SO(4)-20MO-60P(2)O(5): 1.0Ho(2)O(3)/1.0Er(2)O(3) (M=Mg, Ca, and Ba) have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350-2100 nm were studied at ambient temperature. The spectra were characterized using Judd-Ofelt theory. From the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for blue (B), green (G) and red (R) emission levels of these glasses have been evaluated. The energy transfer between the two rare earth ions (Ho(3+) and Er(3+)) in co-doped Na(2)SO(4)-MO-P(2)O(5) glass systems in the visible and NIR regions has also been investigated. Highest intensity, the highest quantum efficiency and maximum energy transfer with low phonon losses of B, G, and R lines has been observed in BaO mixed glasses. The reasons for such higher values of these parameters have been discussed in the light of varying field strengths at the rare earths ion site due to replacement of one modifier oxide with the other. The enhanced intensity of NIR emission (at 2.0 μm) has also been discussed in terms of cross relaxation of Er(3+) ions from (4)I(13/2) level to (5)I(7) of Ho(3+) ions.

Spectral and fluorescent kinetics features of Nd3+ ion in Nb2O5, Ta2O5 and La2O3 mixed lithium zirconium silicate glasses.

Li(2)O-ZrO(2)-SiO(2):Nd(3+) glasses mixed with Nb(2)O(5), Ta(2)O(5) and La(2)O(3) were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The Judd-Ofelt theory was successfully applied to characterize Nd(3+) spectra of all the three glasses. From this theory, various radiative properties like transition probability A, branching ratio β(r), the radiative lifetime τ(r), for (4)F(3/2) emission level in the spectra of these glasses has been evaluated. The radiative life time for (4)F(3/2) level of Nd(3+) ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied, the La(2)O(3) mixed glass has exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Nd(3+) ions.

Spectroscopic features of Ni2+ ion in PbO–Bi2O3–SiO2 glass system

Glasses of the composition (30-x)PbO-5Bi2O3-65SiO2: xNiO (with x ranging from 0 to 1.0 mol%) were synthesized. A variety of spectroscopic studies, viz., IR, Raman optical absorption and luminescence properties of these glasses have been carried out as a function of NiO concentration. The analysis of results of all these studies has indicated that the nickel ions occupy both octahedral and tetrahedral positions. However, with the increase of NiO concentration the octahedral occupancy of Ni(2+) ions prevailed over the tetrahedral ions. The luminescence spectra of these glasses have exhibited a broad NIR emission band in region 1100-1500 nm. This band is identified as being due to (3)T2(3F)→(3)A2(3F) octahedral transition of Ni(2+) ions. The luminescence efficiency and cross section have been found to be the highest for the glass containing the highest concentration of NiO. The reasons for such high luminescence efficiency have been discussed in the light of structural variations taking place in the host glass network.