Spectroscopic analysis of Eu3+ in single-crystal hexagonal phase AlN

A detailed spectroscopic analysis of the crystal-field splitting of the energy levels of Eu3+(4f(6)) in single crystals of hexagonal phase aluminum nitride is reported based on assignments made to the high-resolution cathodoluminescence spectra observed between 500 nm and 750 nm obtained at 11 K and room temperature. Single crystals doped with trivalent europium were grown by high pressure, high temperature technology, and the crystal structure was confirmed by x ray diffraction methods to be the hexagonal phase. The Eu3+ ions substitute for Al3+ ions in sites of C-3v symmetry during crystal growth. More than 97% of the observed spectra are attributed to Eu3+ in the majority site. The spectra are identified as transitions from the excited D-5(0) and (5)D(1)multiplets of Eu3+ to the ground-state multiplets F-7(0), F-7(1), F-7(2), F-7(3), F-7(4), F-7(5), and F-7(6) split by the crystal field into energy (Stark) levels. A parameterized Hamiltonian defined to operate within the 4f(6) electronic configuration of Eu3+ was used to model the experimental Stark levels and their symmetry assignments or irreducible representations (irreps). The crystal-field parameters were determined through use of a Monte Carlo method in which the six B-q(k) were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting, which involved 20 Stark levels and their irreps from D-5(1), D-5(0), and F-7(0-4), resulted in a rms deviation of 6.7 cm(-1). The predicted splitting of the F-7(5) and F-7(6) multiplets was used to assign the experimental splitting for these manifolds since the spectra involved are weak and broad, precluding detailed Stark-level assignments. (C) 2011 American Institute of Physics. [doi:10.1063/1.3609076]