Spectroscopy and upconversion processes in YAlO3:Ho3+ crystals

Emission from the high lying excited states, energy transfer, and upconversion processes are investigated in YAlO3:Ho3+. Selectively excited emission spectra in the range from 300 to 800 nm starting from the D-3(3), (3)G(5), F-5(3), S-5(2) and F-5(5) multiplets were measured at 15 K. This, together with the detailed absorption and excitation measurements at 15 K allowed determination of the Stark energy levels of Ho3+ ions in YAlO3 up to UV energies. The S-5(2) fluorescence decays were recorded as a function of temperature and Ho3+ concentration in order to investigate the process of quenching of fluorescence due to cross relaxation among two ions. Conversion of red and infrared laser radiation to green S-5(2) and blue F-5(3) emission is reported. Under pulsed resonant excitation of the F-5(5) or I-5(5) levels the upconversion was found to be due to energy transfer process between two excited ions. The photon avalanche effect was observed under cw excitation around 585 nm. (C) 1999 Elsevier Science B.V. All rights reserved.