Optical properties of Eu2+Eu2+ ions in BaY2F8BaY2F8 for completely-solid-state cw UV laser emission

Eu-doped BaY2F8BaY2F8 single crystals have been grown with two different Eu ion concentrations: 0.5%, 1% Eu doping levels. It was found that part of the Eu3+Eu3+ ions added in the melt were reduced during the growth process and the ratio between the Eu2+Eu2+ and Eu3+Eu3+ content in the crystal depends on the duration of the growth process. A complete room-temperature polarized spectroscopic characterization of the divalent Eu ions in this host crystal is presented with particular insights in the laser potentialities of the compound in the UV region. Polarized absorption, emission and excitation spectra are presented together with the lifetime measurement of the emitting level. It was found that due to the weak nephelauxetic effect the 4f7→4f65d14f7→4f65d1 band is located at higher energy than the 4f→4f(8S7/2→6P7/2)4f→4f(8S7/2→6P7/2) transition. As a result, when pumped in the 200–300nm range, this crystal shows an interesting emission that extends from 351 to 366 nm and has a decay-time as long as τ=(1.5±0.1)ms. This opens the possibility to obtain completely-solid-state laser emission in the UV region with potentialities for cw or mode-locked emission.