Rare Earth Centres in Mixed Compound Crystals

A review of the Yb impurity related centres in mixed InP-based crystals has been presented. It is shown that Yb$\text{}^{3+}$ ions can be utilized to probe alloy disorder, both in cationic (GaInP) and anionic (InPAs) alloys. The existence of alloy disorder manifested itself in the photoluminescence spectra reflecting local atomic structure of the Yb centres. The dominant emissions have been ascribed to the Yb-P$\text{}_{4}$Ga$\text{}_{12}$ and Yb-P$\text{}_{4}$-Ga$\text{}_{11}$In complexes in GaInP and to Yb-P$\text{}_{4}$ and Yb-P$\text{}_{3}$As centres in InPAs. The excitation and relaxation mechanisms of the 4f-shell of Yb$\text{}^{3+}$ ions were also investigated. It was found that the temperature quenching of the Yb$\text{}^{3+}$ luminescence was accompanied with the appearance of two thermally activated photoluminescence bands. It is suggested that photoluminescence at an energy of 25 meV below the energy gap is due to recombination of excitons bound at Yb-related centres. Relaxation of the excited 4f-shell of Yb$\text{}^{3+}$ ions proceeds via back transfer of the excitation energy from the 4f-shell to excitons bound at Yb-centres.