In this article, we have investigated energy upconversion process in erbium doped oxyfuoride tellurite glasses exciated with 980 nm diode laser. The glasses used in measurements are with a mol% composition of 70TeO2-9PbF2-190AlF3-10BaF2-1Er2O3. The Ωs intensity parameters, the radiative rates, the branching ratios and the fluorescence lifetimes were calculated based upon the Judd-Ofelt theory and the experimental absorption spectrum. Under 980 nm excitation, efficient 530, 544, and 665 nm upconversion emission are due to two-photon absorption processes.
The solution precipitation is used to synthesize the Tb doped yttrium phosphates. The as-synthesized is the monoclinic phased YPO4×2H2O with churchite-type structure, which is transformed to the tetragonal phased YPO4 with xenotime-type structure as the temperature approaches 200°C during the thermal treatment process. This phase transformation process can not be observed in some routes that need a higher synthetic temperature, in which, only a high-temperature phase is obtained. The luminescent efficiency dependence on the heat-treatment temperature is investigated. The luminescent efficiency presents a two-step increase respectively around 300 and 700°C. Results indicate that the significant increase of luminescent efficiency at 300°C is not related to the phase structure transformation, but to the decrease of OH- ions content, and that the significant increase of luminescent efficiency at 700°C is related to the increase of crystallinity, which may increase the absorption to VUV light.
Ce-, Tb-doped and co-doped YBO3 were prepared by solid-state reaction. The structure of the powder is identified as vaterite-type structure. The photoluminescence of the samples under UV/ VUV excitation were investigated. The results indicate that the energy is transferred between Ce3+ and Tb3+ under UV excitation while Ce3+ is not beneficial to the emission of Tb3+ under VUV excitation due to the different luminescence mechanism. The blue emission of Tb3+ was observed at low Tb3+ concentration and disappeared at high activator concentration due to the relaxation.
Bulk Y2O3: Eu (1% in molar ratio) powders and nanocrystals with different particle size were prepared by chemical self-combustion, all of them exhibits cubic structure. Fluorescent decay curves at room temperature and 10k, excitation and emission spectra were measured. The dependence of fluorescence lifetime on the particle size and temperature were discussed. Meanwhile, the quantum efficiency of 5D0 level of europium ion occupying C2 site was estimated.
From the optical absorption measurements, the Judd-Ofelt parameters were computed using Judd-Ofelt theory. According to the radiative lifetime obtained from the Judd-Ofelt parameters and the measured lifetime, the1.5μm quantum efficiency was calculated. The quenching effect of OH upon the lifetime of 1.5μm emission was investigated. From the absorption sideband measurement of glass host, the value of optical band gap was estimated. The McCumber theory was used to calculate the stimulated emission cross-section and in approximate agreement with experimental one if the emission spectrum could be obtained accurately. The gain coefficient spectra were computed.
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