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Crystal field absorption and emission spectra originated by 5I8 ↔ 5F5 transitions, due to Ho3+ (1% molar fraction) in a YPO4 single crystal, were investigated in the 15000 to 16000 cm-1 range. Fourier Transform high resolution absorption measurements, performed in the 9 to 300 K range, and photoluminescence, monitored at 10 K upon 540 nm excitation, supplied the sublevel separations within both 5I8 and 5F5 manifolds. The sublevel positions were compared to those calculated by diagonalization of the full 4f-configuration matrix in the framework of a single-ion model. The results are discussed also in relation with experimental data previously reported for similar systems containing Ho3+. [ABSTRACT FROM AUTHOR]

Several weak absorption bands have been observed in the optical absorption spectra of pure and rare-earth-doped YAl3(BO3)4 single crystals in the 3350– 3650 cm−1 wave number region. Two of them, peaking at about 3377 cm−1 and 3580 cm−1 in the 8 K spectra, appear in most of the samples. They are tentatively attributed to the stretching mode of OH− ions incorporated in the crystal during the growth. An additional absorption band at about 5250 cm−1 at 8 K has also been detected in almost all samples. The temperature and polarization dependences of these bands, and their possible origin, are discussed. [ABSTRACT FROM AUTHOR]

Abstract: FTIR spectroscopy is applied to monitor the effects caused by fluorinated precursors (1–10mol%) in the sol–gel synthesis of silica glasses, either pure or doped with Ce and Er. In pure samples the Si–OH level is heavily reduced to ∼3×10−3 mol%. In doped samples the effect is more limited. The presence of residual fluorine, proved by the Si–F vibrational absorption at ∼950cm−1, causes deep changes in the rare-earth (RE) crystal field spectra, which are characterized by narrow absorption lines. The lines broaden if the temperature is increased from 9 to 300K. The result is discussed in terms either of local ordering around the rare earth ion or by its partial decoupling from the disordered host matrix, due to the creation of network terminating sites. [Copyright &y& Elsevier]