D.K. Rai

Optical properties of Sm3+ ions doped in tellurite glass.

Judd-Ofelt analysis of Sm(3+) ions doped in a tellurite glass has been accomplished. Fluorescence and life-time measurements have been carried out using Ar(+) laser and excimer laser. Stark splitting has been observed in the upper and lower levels in fluorescence. The life-time of 4G(5/2) level as a function of Sm(3+) concentration has been measured. Concentration quenching and the mechanism responsible for the same have been found.

Optical studies of Eu3+ ions doped in tellurite glass.

Absorption and fluorescence spectra of Eu3+ ions doped in a tellurite glass have been recorded and analysed. Judd-Ofelt analysis has been done in order to calculate the different optical parameters such as oscillator strength, Judd-Ofelt intensity parameters, stimulated emission cross-section, transition probability, branching ratio, radiative lifetime, etc. Lifetime measurements of the 5D0 level as a function of Eu3+ concentration have been used to explore the concentration quenching process. The mechanism of quenching is found to be of a dipole-dipole type.

Optical properties of Sm3+ doped calibo glass with addition of lead oxide.

Optical absorption and fluorescence spectra of Sm3+ doped calibo glasses and the effects on these on addition of lead oxide have been recorded. The concentration of lead oxide has been varied from 0 to 30 mol%. The Judd-Ofelt intensity parameters Omegalambda (lambda=2, 4, 6) for f-f transitions in Sm3+ ions trapped in these glasses are calculated and their variation with increase in proportion of lead oxide has been discussed. It is observed from the fluorescence spectra that the intensity of fluorescence reaches a maximum when 20% of PbO is present. Stimulated emission cross-section is calculated and compared with its value for other lattices.

Optical properties of Dy3+ doped calibo glass on addition of lead oxide.

The effects of PbO on optical properties of dysprosium doped calibo glass have been studied. The content of PbO in the glass has been varied from 0 to 60 mol%. The absorption and fluorescence spectra are analyzed in terms of the Judd-Ofelt theory. It is observed that the fluorescence yield is maximum for the glass containing 40 mol% PbO. The I-R absorption spectra of these glasses have also been recorded and interpreted in terms of changes in the structure of the glasses.

Light-into-heat conversion in La 2 O 3 :Er 3+ -Yb 3+ phosphor: an incandescent emission

Low-power-threshold cw laser-induced incandescence (CWLII) has been observed in La(2)O(3):Er(3+)-Yb(3+) phosphor on excitation by a 976 nm IR laser. It is suggested that incandescence originates from the extensive heating induced by the nonradiative processes taking place following the laser excitation. Other mechanisms for similar observations have also been suggested in the literature and have been discussed with the present observations. The estimated temperature for the CWLII approaches around 2650 K, and this seems to provide an effective way to rapidly attain high temperature in nano/microvolumes of phosphor. The phosphor exhibited efficient upconversion, and the ratio of the (2)H(11/2)→(4)I(15/2) and (4)S(3/2)→(4)I(15/2) band intensities of Er(3+) permits measurement of the temperature rise, from a distance.

White light upconversion emissions from Tm3++Ho3++Yb3+ codoped tellurite and germanate glasses on excitation with 798 nm radiation

White light has been produced using 798 nm laser excitation in Tm3++Ho3++Yb3+ codoped tellurite and germanate glasses. These glasses simultaneously generate the three primary colors, red, green, and blue, on 798 nm excitation. Thus, multicolor emission obtained was tuned to white luminescence by adjusting the Ho3+ ion concentration and excitation power. UV excitation and fluorescence spectra of these triply doped glasses give additional emissions, which do not appear on 798 nm excitation.

Effect of thermal neutron irradiation on Gd3+ ions doped in oxyfluoroborate glass: an infra-red study

Infrared spectra of oxyfluoroborate glasses of composition (70-x)H{sub 3}BO{sub 3}+20Li{sub 2}CO{sub 3}+xGd{sub 2}O{sub 3}, where x=0, 0.5, 1.0, 3.0 and 5.0 mol%, have been recorded to explore the role of Gd{sup 3+} ions in the structure of the glasses. We concluded that Gd{sup 3+} ion behaves as a glass modifier. The effect of thermal neutron irradiation on the structure of these glasses also has been explored and the changes compared with earlier results on {gamma}-irradiation.

Magnetic-field-induced optical bistability in multifunctional Gd 2 O 3 :Er 3+ ∕Yb 3+ upconversion nanophosphor

The effect of an external magnetic field (0-1 T) on the upconversion emission (lambda(exc)=976 nm) of Gd(2)O(3):Er(3+)Yb(3+) nanocrystalline phosphor has been studied. Optical bistability (hysteresis behavior in the intensity of the optical emission) for different transitions of the Er(3+) ion has been observed for a complete cycle of the magnetic field between 0 and 1 T. The phosphor shows paramagnetic behavior, consistent with the presence of Gd(3+) ions, at room temperature. Interaction between induced magnetization in the Gd(2)O(3) host and the intrinsic magnetic moment of the nanosized clusters of Er(3+) and Yb(3+) ion pairs is proposed to be responsible for the hysteresis behavior.

Spectroscopic studies and normal coordinate analysis of bilirubin

The infrared spectrum of bilirubin has been recorded in the spectral region 200-4000 cm(-1). The Raman spectrum has also been recorded using the second harmonic (530 nm) radiation of a 200 mW Nd-YAG laser. In order to confirm the vibrational assignment of the bands obtained from experimental observation, a normal coordinate analysis has been carried out using the semi-empirical AM1 method through MOPAC 5.1 computer program. Electronic absorption spectrum of bilirubin dissolved in CHCl3 has been recorded in the spectral region 300-600 nm. A broad spectrum is observed with peak maxima at 454.2 nm. The photoacoustic spectrum of this molecule (in the powder form) has also been recorded for the first time which shows certain discrete features.

Photoacoustic Studies on Neutron-Irradiated Rare Earth Oxide Powers

The effect of neutron irradiation on the photoacoustic spectra of Er2O3 and Nd2O3 in powder form has been studied. The irradiation shows a quenching effect on the photoacoustic signal which regains its intensity after a lapse of some time. It is believed that the irradiation changes the oxidation state of the rare-earth ions from M3+ to M2+. The half-life of the recovery process Er2+ to Er3+ in the case of irradiated Er2O3 is found to be 46 h.