Eu3+-doped beta-Ga2O3 nanophosphors: annealing effect, electronic structure and optical spectroscopy

A comprehensive survey of electronic structure and optical properties of rare-earth ions-doped semiconductor is of vital importance for their potential applications. In this work, Eu3+-doped beta-Ga2O3 nanocrystals were synthesized via a combustion method. The evolution of the optical properties of nanophosphors with increasing the annealing temperature was investigated in detail by means of excitation and emission spectra at room temperature and 10 K. Eu3+ ions were proved to be incorporated into the crystal lattice of the beta-Ga2O3 phase after annealing the as-prepared nanoparticles at 1100 degrees C. It was observed that the substitution of Eu3+ for Ga3+ occurred at merely single site, in spite of two crystallographically nonequivalent sites of Ga3+ in beta-Ga2O3. Spectroscopic evidence corroborated and clarified the local symmetry of C-s for Eu3+ at this single site. From the high-resolution excitation and emission spectra, 71 crystal-field levels of Eu3+ in beta-Ga2O3 were identified and analyzed in terms of 19 freely varied free-ions and crystal-field parameters based on C-s symmetry. The standard deviation of the final fitting is as low as 12.9 cm(-1), indicating an excellent agreement between experimental and calculated energy levels. The temperature-dependent luminescence dynamics of the D-5(0) multiplet for Eu3+ in beta-Ga2O3 phosphors has also been revealed for the first time from 10 to 300 K.