Thermal quenching of luminescence and isovalent trap model for rare-earth-ion-doped AlN

Investigations of the luminescent properties of Pr-, Eu-, Tb- and Tm-implanted AlN thin films at temperature in the range 9-830 K are reported. The temperature studies of photoluminescence and cathodoluminescence spectra revealed unexpectedly weak thermal quenching for all investigated rare earth (RE) ions. The maximum CL emission is observed from Eu (red) at 485 K, Tb (green) at 590 K and Tin (blue) at 530 K, respectively. For Tb- and Tm-doped AlN samples, temperature-dependent crossrelaxation processes were observed. Photoluminescence excitation spectra, obtained under UV excitation in the spectral range 200-400 nm, exhibit several bands. It is proposed that the RE ions exist in semiconductors as isolated ions (singlet), nearest-neighbor (nn) ion pairs (dimer), and three ions (trimer). The Koster-Slater and simple spherical potential-well models for RE-structured isovalent (RESI) hole trap are proposed. The exciton binding energies of RESI traps are calculated and compared with experimental thermal-quenching energies. The energy-transfer processes between the AlN host and the 4f-shell systems are emphasized as the main mechanisms for thermal-quenching processes rather than nonradiative decay of 4f transitions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.