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Abstract: Rare-earth-doping and various post-growth heat treatments effects on OH− absorption in singly Er- and Yb-doped, doubly Er/Mg- and Er/Yb-doped LiNbO3 crystals have been investigated. The OH− absorption in the rare-earth-doped crystals shows definite anisotropy and is stronger in a Z-cut plate. Rare-earth-doping causes considerable OH− absorption reduction. MgO-codoping induces additional reduction. Slight/heavy rare-earth-doping causes slight/considerable spectral shape change. Thermal reduction treatment causes OH− absorption vanishing whether the crystal is originally congruent or near-stoichiometric. Further oxidation treatment renders the absorption reemerged. Li-rich vapor transport equilibration (VTE) treatment causes significant absorption decrease. For a slightly rare-earth-doped Li-rich VTE-treated crystal, its spectral feature is similar to that of the undoped near-stoichiometric crystal; for a heavily rare-earth-doped VTE-treated crystal, its spectral shape preserves the feature of the heavily rare-earth-doped as-grown crystal. For the Er/Mg-codoped crystal studied, the Li-rich VTE also induces an abrupt conversion of peaking position from 3483 cm−1 to 3535 cm−1. The absorption in the Li-rich VTE-treated crystals also reveals aging effects in spectral shape, peaking position and absorption intensity. Li-poor VTE induces significant absorption increase. In addition, the effect of OH− presence on lifetime of Er3+ emission at 1.5 μm was also studied. The results show that the effect is small for the as-grown congruent crystals and slight for Li-rich VTE-treated ones. [Copyright &y& Elsevier]

Dispersion relation is established for Er(NbO 3) 3 phosphor, which is an excellent candidate for optical thermometry based on thermal effect of Er3+ fluorescence intensity ratio. To achieve it, Er(NbO 3) 3 phosphor was dispersed into α-bromonaphthalene liquid to form a suspension. Then, refractive index values of the suspension were measured at wavelengths 473, 589.3, 632.8, 980, 1311 and 1553 nm by dropping it onto a plastic sheet. Subsequently, refractive indices of the Er(NbO 3) 3 phosphor were evaluated from these measured index values using Maxwell-Garnett relation. Finally, based on these Er(NbO 3) 3 index values, which have an error 0.03, a three-oscillator Sellmeier equation that considers contributions from Nb–O group, plasmons in far UV regime and phonons in infrared region is established. In parallel, a Cauchy dispersion equation is also established. Both equations can well fit the experimental data and the refractive indices predicted by the two equations can be regarded as identical within the error 0.03. Refractive indices of Er(NbO 3) 3 phosphor at different wavelengths ranging from 473 to 1553 nm have been obtained from the index values measured from an α-bromonaphthalene mixture suspended with Er(NbO 3) 3 phosphor grains. A three-oscillator Sellmeier equation n2(λ) = B UV - B IR λ2 + B 3 /(λ 3 −2-λ−2) is proposed that considers the contributions from plasmons in far UV, phonons in infrared region and the Nb–O group. A Cauchy dispersion equation n(λ) = A + B/λ2 + C/λ4 + D/λ6 is also attempted to fit the experimental data. The fitting results show that both equations can give accurate prediction of the refractive index value of the Er(NbO 3) 3 phosphor and have an accuracy better than 0.03 satisfying the demand for Judd-Ofelt spectroscopic analysis. Image 1 • Refractive indices of Er(NbO 3) 3 powder were measured at different wavelengths. • A three-oscillator Sellmeier equation n2(λ) = B UV -B IR λ2+B 3 /(λ 3 −2-λ−2) is suggested. • A Cauchy dispersion equation n(λ) = A + B/λ2+C/λ4+D/λ6 is also established. • Both equations give accurate prediction of refractive index value of Er(NbO 3) 3. • Both equations have an accuracy 0.03 satisfying demand for Judd-Ofelt analysis. [ABSTRACT FROM AUTHOR]