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Abstract: Er3NbO7 phosphor was synthesized by sintering a mixture of Er2O3 and Nb2O5 powder in a molar ratio of 3:1 at 1600°C over 55h. Optical absorption and emission characteristics of Er3+ ions in the calcined Er3NbO7 powder were investigated and discussed compared with ErNbO4 phosphor and a Z-cut congruent Er (2mol%):LiNbO3 single crystal. The absorption and emission studies show that, due to different crystal structures, the spectroscopic properties of these niobates have some differences in spectral shape, peak position, and relative intensity, especially at 1.5μm. The most obvious spectral feature of the Er3NbO7 is that the spectral structure of band instead of peak is observed in its absorption or emission spectrum due to the existence of local structural disorder and multiple Er3+ sites. The Er3NbO4 shows stronger upconversion emission than the single crystal but weaker than the ErNbO4. Experimental results show that energy transfer upconversion and/or excited state absorption play a dominant role in the upconversion emissions, and, at higher pump level (>200mW), the thermal effect becomes significant and results in drop of the upconversion intensity. The 1.5μm lifetimes of Er3+ ion in the Er3NbO7, ErNbO4 phosphor, and in the Er:LiNbO3 crystal are measured to be ∼5.3, 2.0, and 2.4ms, respectively. In combination with the measured Raman spectra, the quantum efficiency, multiphonon nonradiative decay rate, and theoretical radiative lifetime of the 1.5μm emission of the two powder materials are expected. The differences in upconversion intensity and measured 1.5μm lifetime between the three materials are explained qualitatively. [Copyright &y& Elsevier]

Visible and near infrared absorption and emission (488 nm excitation) characteristics of ErNbO4 powder, which were prepared by calcining the Er2O3 (50 mol%) and Nb2O5 (50 mol%) powder mixture at 1100 and 1600 °C for different durations, have been investigated at room temperature. The absorption and emission characteristics of these calcined ErNbO4 powder were summarized and discussed in comparison with those of Er2O3. Weak emission of Er2O3 relative to the calcined ErNbO4 is mainly conducted with absorption difference at the excitation wavelength 488 nm. The obvious spectral changes from Er2O3 to calcined ErNbO4 samples are related to an elevated-temperature-assisted phase transformation according to the solid-state chemical reaction equation: Er2O3 + Nb2O5 ⇌ 2ErNbO4, which results in the changes of the ion environment of Er3+ and hence changes of the Stark levels of Er3+. The further spectral change as the strengthened calcination results from the improvement of ErNbO4 purity in the calcined mixture. The borders between two green transitions and between two near infrared transitions in the emission spectra of both calcined samples and Er2O3 were tentatively identified by referencing earlier reported emission spectra of the precipitated Z-cut VTE Er(2.0 mol%):LiNbO3 crystal and the match relation between absorption and emission spectra of the ErNbO4 powder. A comparison was performed on the spectra of calcined ErNbO4 powder and those of VTE Er(2.0 mol%):LiNbO3 crystals. The results allow to preliminarily deem the contribution of ErNbO4 precipitates, generated inside these crystals by the VTE procedure, to the spectra of these crystals. [Copyright &y& Elsevier]

At room temperature, alpha-polarized absorption spectra of as-grown and annealed Er3+/Yb3+ co-doped, Z-cut LiNbO3 single crystals, grown by using Czochralski method, were measured in the wavelength range of 300-1 650 nm. The spectroscopic properties of Er3+ were analysed by using Judd-Ofelt theory. The experimental values of the electron transition strengths of several major transitions from the ground state to excited-state manifolds were evaluated from the measured integrated absorption coefficients of Er3+. The Judd-Ofelt parameters were determined by using least square method. According to the fitted Judd-Ofelt parameters, the spontaneous emission rates, the fluorescence branch ratios from the excited-state manifolds J to the lower-lying manifolds J', as well as the radiative lifetimes of the excited states were numerically calculated. In addition, Yb3+ co-doping and thermal anneal effects on the spectroscopic properties of Er3+ were also considered in this work.