V.V. Ravi Kanth Kumar

Optical properties of Nd3+ doped bismuth zinc borate glasses.

Glasses with compositions of (100-x) (Bi2ZnOB2O6) -x Nd2O3 (where x=0.1, 0.3, 0.5, 1 and 2 mol%) were prepared by melt quenching method and characterized through optical absorption, emission and decay curve measurements. Optical absorption spectra have been analyzed using Judd-Ofelt theory. The emission spectra exhibit three peaks at 919, 1063 and 1337 nm corresponding to (4)F3/2 to (4)I9/2, (4)I11/2 and (4)I13/2 transitions in the near infrared region. The emission intensity of the (4)F3/2 to (4)I11/2 transition increases with increase of Nd(3+) concentration up to 1 mol% and then concentration quenching is observed for 2 mol% of Nd(3+) concentration. The lifetimes for the (4)F3/2 level are found to decrease with increase in Nd2O3 concentration in the glasses. The decay curves of the glass up to 0.3 mol% of Nd(3+) exhibit single exponential nature and thereafter the curves become nonexponential nature (0.5, 1 and 2 mol%). The nonexponential curve has been fitted to the Inokuti-Hirayama model to understand the nature of energy transfer process.

Fluorescence properties and electron paramagnetic resonance studies of γ-irradiated Sm3+-doped oxyfluoroborate glasses

The permanent photoinduced valence manipulation of samarium doped oxyfluoroborate glasses as a function of γ-ray irradiation has been investigated using a steady-state fluorescence and electron paramagnetic resonance techniques. An increase in SrF2 content in the glass led to the red shift of the peaks in as prepared glass, while in irradiated glasses this led to the decrease in defect formation as well as increase in photoreduction of Sm3+ to Sm2+ ion. The energy transfer mechanism of induced permanent photoreduction of Sm3+ to Sm2+ ions in oxyfluoroborate glasses has been discussed. The decay analysis shows exponential behavior before irradiation and non-exponential behavior after irradiation. The energy transfer in irradiated glasses increases with the increase in SrF2 content in the glass and also with the irradiation dose.

Third order nonlinear optical properties of bismuth zinc borate glasses

Third order nonlinear optical characterization of bismuth zinc borate glasses are reported here using different laser pulse durations. Bismuth zinc borate glasses with compositions xBi2O3-30ZnO-(70-x) B2O3 (where x = 30, 35, 40, and 45 mol. %) have been prepared by melt quenching method. These glasses were characterized by Raman, UV-Vis absorption, and Z scan measurements. Raman and UV-Vis spectroscopic results indicate that non-bridging oxygens increase with increase of bismuth content in the glass. Nonlinear absorption and refraction behavior in the nanosecond (ns), picosecond (ps), and femtosecond (fs) time domains were studied in detail. Strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with both ps and fs excitations. In the case of ns pulse excitations, TPA and free-carrier absorption processes contribute for the nonlinear absorption. Two-photon absorption coefficient (β) and the absorption cross section due to free carriers (σe) are estimated by theoretica...

Photoluminescence properties of Tb-Eu-Mn-codoped fluoroborate glasses under γ-irradiation

We report here an energy transfer from Tb3+ to Eu3+, Mn2+ and Eu2+ to Tb3+ and Mn2+ for an un-irradiated and γ-irradiated B2O3-Al2O3-Na2O-SrF2 glass samples, respectively. The blue emission from Eu2+ ions as well as green and red emission from Tb3+, Eu3+, and Mn2+ ions will contribute to the generation of white light while excited at 339 nm using a xenon lamp. Furthermore, the chromaticity color coordinates, correlated color temperature, and quantum efficiency parameters are calculated for all the glass samples, and their relative variations with respect to γ-irradiation dose are presented.

Synthesis, characterization and photoluminescence of Eu3+, Ce3+ co-doped CaLaAl3O7 phosphors

Powder phosphors of CaLa1− x Eu x Al3O7, CaLa1− x Ce x Al3O7 and CaLa0.99− x Eu x Ce0.01Al3O7, where x = 0.01, 0.03, 0.05 and 0.07, were prepared by a combustion method. The powders were well characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence techniques. Emission spectra of Eu3+-doped powder phosphors showed strong red emission at 613 nm (5D0 → 7F2); no concentration quenching was observed. Generally, Ce3+ acts as an efficient sensitizer when doped with other trivalent lanthanide ions. However, interestingly, in the CaLaAl3O7 powder phosphors, the addition of Ce3+ with Eu3+ exhibited an adverse effect–decreased photoluminescence intensity. The reasons for this behavior are discussed.

Luminescence performance of Eu3+-doped lead-free zinc phosphate glasses for red emission

In this study, the luminescence performance of zinc phosphate glasses containing Eu3+ ion with the chemical compositions (60–x)NH4H2PO4-20ZnO-10BaF2-10NaF–x Eu2O3 (where x = 0.2, 0.5, 1.0 and 1.5 mol%) has been studied. These glasses were characterized by several spectroscopic techniques at room temperature. All the glasses showed relatively broad fluorescence excitation and luminescence spectra. Luminescence spectra of these glasses exhibit characteristic emission of Eu3+ ion with an intense and most prominent red emission (614 nm), which is attributed to 5D0 → 7F2 transition. Judd-Ofelt (Ω2, Ω4) parameters have been evaluated from the luminescence intensity ratios of 5D0 → 7FJ (where J = 2 and 4) to 5D0 → 7F1 transition. Using J-O parameters and excitation spectra, the radiative parameters are calculated for different Eu3+-doped glasses. Effect of γ-irradiation at fixed dose has been studied for all the Eu3+-doped glass matrices. The lifetimes of the excited level, 5D0, have been measured experimentally through decay profiles. The colour chromaticity coordinates are calculated and represented in the chromaticity diagram for Eu3+-doped zinc phosphate glasses for all concentrations.

Energy transfer and color tunability in γ-irradiated Tb3+-Sm3+ codoped B2O3-Al2O3-SrF2 glasses

The present paper mainly focused on the tunable luminescence and energy transfer from Tb3+ to Sm3+; Sm3+ to Sm2+ ion in B2O3-Al2O3-SrF2 glasses. Moreover, the characteristic parameters of lighting materials are calculated and discussed systematically.