Spectroscopy of Ho:Lu2O3 with respect to the realization of a visible laser

Recent progress in the development of GaInN laser diodes in the blue region enables solid-state lasers in the visible spectral range without frequency conversion. This was demonstrated to be a highly efficient process in for example praseodymium doped materials [1]. But also the trivalent holmium ion provides absorption lines in the blue spectral region and emission lines around 550 nm. However, so far laser action on this transition has only been realized at low temperatures [2,3]. Since the energy gap between the thermally coupled ⁵S2 and ⁵F4 manifolds - the initial states of the green emission - and the adjacent ⁵F5 level is only about 2700 cm⁻¹, low phonon hosts as for example Lu2O3 (Eeff,phon = 550 cm⁻¹) are required to minimize non-radiative losses. We report a fundamental spectroscopic research of Ho:Lu2O3 in order to evaluate the laser potential of the green transition. Crystals were grown by the Heat-Exchanger and Nacken-Kyropoulos method and the spectroscopic investigations include temperature dependent lifetime measurements as well as the determination of the ground state absorption, the excited state absorption, and the emission cross sections.