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Abstract: Influence of thermal reduction on intrinsic (bipolarons), extrinsic (Er3+) defects and OH− groups in Er:LiNbO3 crystals, which were as-grown and VTE-treated (VTE: vapor transport equilibration) before being reduced, was studied by measuring the polarised or unpolarised optical absorption in visible and near infrared regions. A wide and strong band extending from the optical absorption edge up to the infrared region and peaking around 500nm (∼2.5eV), resulting from the absorption of reduction-induced bipolarons, is observed. Meanwhile, the thermal reduction also induces an additional, relatively much narrow absorption band around 370nm in a crystal whether it is Er-doped or undoped and whether it is congruent or originally VTE-treated. Both the 500nm and the 370nm bands show similar polarisation dependence. The thermal reduction treatment hardly influences Er3+ spectroscopic properties such as absorption amplitude, linewidth, peaking position and polarisation dependence. The original VTE effects on the spectroscopic properties of Er:LiNbO3 crystal are essentially retained still. The thermal reduction has a similar effect on the OH− absorption to a strong VTE treatment: the removal of the OH− groups contained in the crystal. [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]

A previous paper [J. Lumin. 177 (2016) 219] has studied Judd-Ofelt spectroscopic properties of Er3+ (0.5 at%)-doped Gd 3 (Al, Ga) 5 O 12 garnet single-crystal, and reported the Judd-Ofelt intensity parameters Ω 2 = 1.47 × 10−20 cm2, Ω 4 = 1.38 × 10−20 cm2 and Ω 6 = 1.19 × 10−20 cm2. We have performed a re-study on the Judd-Ofelt spectroscopic properties of a similar garnet single-crystal Er3+(20 at%)-doped Gd 3 (Al 0.4 Ga 0.6) 5 O 12 , and obtained quite different values of Judd-Ofelt intensity parameters Ω 2 = (0.34 ± 0.11) × 10−20 cm2, Ω 4 = (0.48 ± 0.16) × 10−20 cm2 and Ω 6 = (1.05 ± 0.17) × 10−20 cm2. The quite different Ω t values given by two studies are mainly due to remarkably different absorption characteristics of Er3+ in the crystals employed in two studies, and factors that lead to quite different absorption characteristics are discussed. Another reason is that the hypersensitive transition at 380 nm was excluded from the Judd-Ofelt calculation in that paper, resulting in deviation of their result. Instead, all of the Er3+ absorption bands were included in our calculation, allowing to obtain more accurate Ω t values. Quite different Ω t values lead to considerable differences of relevant spectroscopic parameters, such as radiative rates and lifetimes of typical Er3+ emissions, for which the difference from each other is as much as three times. In addition, visible, near-infrared and mid-infrared fluorescence spectra and lifetimes of Er3+ in the studied crystal were measured, and the emission characteristics are discussed. • Er:Gd 3 (Al,Ga) 5 O 12 crystal was grown and its spectroscopic properties are studied. • Judd-Ofelt analysis was done and the result is compared with previously reported. • The Judd-Ofelt data obtained show large differences from the previously reported. • Main reason is large difference of Er3+ absorption features in two studies. • Sellmeier equation, lattice constant and segregation coefficient are presented. [ABSTRACT FROM AUTHOR]