EVIDENCES OF THE SELF-TRAPPED EXCITONS IN GAPO4 AND ALPO4 CRYSTALS

The self-trapped excitons (STE) are discovered in GaPO4 and AlPO4 crys tals. The PL bands at 2.9 eV with a strong Stoke's shift are excited o nly in the fundamental absorption range of GaPO4 and AlPO4 crystals wi th quantum yield eta about 0.4. Eta(T) possess two stages' thermal que nching with activation energies 0.12 and 0.2 eV for GaPO4 and 0.15 and 0.19 eV for AlPO4. Tau(T) follows eta(T) for both crystals. The non-q uenched values of tau are 0.55 ms and 0.27 ms for GaPO4 and 0.6 ms and 0.33 ms for AlPO4. STE's luminescence is polarized. The degree and th e orientation are different for different stages of STE GaPO4. They co mpose 33% with angle 45-degrees to c axis for low temperature stage an d 8% parallel to c axis for high temperature stage. In AlPO4 crystals both STEs give one orientation with 13% parallel to c axis. At 4.5 K P L decay kinetics split into two components with tau(f) = 0.28 ms and t au(s), = 3 ms for GaPO4 and tau(f) = 0.23 ms and tau(s) = 6 ms for the AlPO4 crystals. These two components are due to the triplet states sp lit in the zero magnetic field. The similarity between STE in GaPO4, A lPO4 crystals and in SiO2 and GeO2 crystals allows to use early propos ed model.