Stokes and anti-Stokes luminescence in LiTaO3:Ho

This paper deals with the excitation and decay of excited state of holmium in LiTaO3 single crystals. Particular attention is paid to processes governing a population build up on the 5S2 and 5I7 metastable states whose quantum efficiencies are sufficiently high to be considered as initial levels for a laser transition. We observed for the first time, to our knowledge, an efficient conversion of the 647.1 nm light of a krypton ion laser into green luminescence in the material studied. Based upon analysis of excited state relaxation dynamics it is concluded that the mechanism involved is the excited state absorption from the long lived 5I7 level. Efficient single wavelength excitation is due to coincidence of transition energies of the ground state absorption and excited state absorption.