R. Balakrishnaiah

Optical spectroscopy, 1.5μm emission, and upconversion properties of Er 3+ -doped metaphosphate laser glasses

Metaphosphate glasses doped with five concentrations of Er3+ ions have been investigated through absorption and emission spectra, decay curves, and upconversion measurements. Judd-Ofelt parameters have been evaluated from absorption spectrum of the 1.0mol.%Er3+-doped glass, which are in turn used to predict radiative properties of some important luminescence levels of Er3+ ions in these glasses. Gain bandwidths of an optical amplifier have been evaluated and are compared with those of reported Er3+:glass systems. Temperature dependence of the 1.5μm emission has been studied for the 2.0mol.%Er3+-doped glass from 13K to room temperature. Lifetimes of the I13/24 level were measured and are found to decrease with concentration of Er3+ ions after 0.1mol.%. Concentration quenching of lifetimes has been analyzed using the theory developed by Auzel [J. Lumin.94-95, 293 (2001); Opt. Mater.24, 103 (2003)]. Infrared to visible upconversion was also measured for three concentrations of Er3+-doped metaphosphate glasses with 794nm excitation. A mechanism, involving excited state absorption and energy transfer upconversion, has been proposed to explain the upconversion process.

Optical spectroscopy and energy transfer in Tm3+-doped metaphosphate laser glasses

Thulium-doped metaphosphate glasses with four concentrations (0.01, 0.1, 1.0 and 2.0 mol%) of Tm 3+ have been prepared and investigated by Raman, absorption and photoluminescence spectral studies. The phonon sideband spectrum has been measured for 1.0 mol% Eu 3+ -doped metaphosphate glass of the same composition and compared with the Raman spectrum. From vibronic spectra, various bands associated with different structural groups have been identified and assigned. Absorption band positions have been used to simulate the complete energ yl evel diagram for the Tm 3+ ion using the model Hamiltonian. Judd–Ofelt parameters have been determined from the absorption bands .U sing these parameters, transition probabilities, excited state lifetimes and transition branching ratios have been evaluated. The emission and decay curves of the 1 D2 level have been measured for all four glass samples both at RT and 15 K. Lifetimes show a strong quenching for Tm 3+ concentrations higher than 0.1 mol%. Fluorescence decay curves of the 1 D2 level have been well fitted to th eI nokuti–Hirayama model for S = 6, suggesting that the mechanism for energy transfer between Tm 3+ ions is of dipole–dipole type.

Fluorescence Properties of Nd3 + -Doped KNbO3 Phosphors

Nd 3+ -doped potassium niobate (K (1―x) NbO 3 :Nd 3+ (x) ) polycrystalline powder phosphors for x = 0.01, 0.03, 0.05, and 0.07 mol were prepared by the conventional solid-state reaction method and were characterized by X-ray diffraction (XRD), field-emission-scanning electron microscopy, transmission electron microscopy, and photoluminescence measurements. The XRD data have shown a single-phase orthorhombic structure for x = 0.01 and 0.03 mol concentrations of Nd 3+ ions, while an additional NdNbO 4 phase is observed at higher concentrations. The photoluminescence spectrum has shown an intense emission band at 1061 nm along with two weak emission bands at 881 and 1343 nm when the samples are excited with 514.5 nm radiation of an Ar + -ion laser. No drastic changes in the intensity of emissions are observed with concentration variation, except slight changes in the intensities and peak positions of crystal-field peaks.