Low temperature microwave study of photoconductivity in rare-earth-doped dielectric crystals

Transient photoconductivity induced by UV (355 nm) laser pulses in doped dielectric crystals CaF2:Sm2+, CaF2:Eu2+ and LSO:Ce3+ was studied by 8-mm microwave technique in a wide range of temperatures, from 300 K down to 5 K. It was possible to study the dynamics of free and bound photoexcited electrons. In LSO:Ce3+, the thermally-activated photoionization process at room temperature changes to a two-step photoionization at liquid helium temperature. In CaF2:Eu2+, two-step photoionization was detected at any temperature and electronic traps cause broadening of the photoconductivity signal at low temperature. In CaF2:Sm2+, the one-step photoionization process was confirmed at any temperature.