Vacuum ultraviolet and ultraviolet spectroscopy of BaMgF4 codoped with Ce3+ and Na+

Ce3+/Na+-doped BaMgF4 (BMF) crystals with a nonlinear property show strong absorption in the vacuum ultraviolet (VUV) and ultraviolet (UV) ranges. Three different fluorescence bands (A, B, C) at 300, 340, and 430 nm were observed when pumped at different wavelengths. Under excitation of the fourth harmonic (266 nm) from a pulsed Nd:YAG laser the BMF crystal changed its colour from transparent to brown due to formation of colour centres. The A, B and C bands are assigned to three different sites of Ce3+: site A is Ce3+ substituting for perfect Ba2+ sites; site B is Ce3+ (Ba2+) perturbed by Na+ as a charge compensator; and site C is a complex composed of Ce3+ and F− vacancies, which trapped one or two electrons.