SPECTROSCOPIC PROPERTIES OF HOLMIUM DOPED LITAO3 CRYSTALS

The spectroscopic properties of Ho3+ ions in LiTaO3 crystals have been investigated using optical absorption, luminescence and lifetime meas urements in the 5-300 K temperature range. The low temperature, polari zed absorption spectra of Ho3+ in this matrix have allowed us to ident ify the Stark levels of the different multiplets up to 30 000 cm(-1). The results are consistent with C-3 symmetry for the rare-earth ions a nd a singlet A character for the lowest Stark level of the I-5(8) grou nd state. Several transitions show additional structure which indicate s multi-site occupancy for the Ho3+ ions. The measured oscillator stre ngths of the transitions between the J manifolds at 300 K are compared with those derived from the Judd-Ofelt theory. The radiative transiti on rates and radiative lifetimes have been calculated. The luminescenc e observed at 5 K has been attributed to S-5(2) --> I-5(8) (18 100 cm( -1)), F-5(5) --> I-5(8) (15 060 cm(-1)) and S-5(2) --> I-5(7) (13 150 cm(-1)) transitions. The obtained data are used to discuss the radiati ve properties for luminescent levels of Ho3+ ions in the LaTaO3 matrix . The emission cross-section of a potential laser line at 2 mu m conne cted with the I-5(7) --> I-5(8) transition is estimated.