We present, to the best of our knowledge, the first laser demonstration of an Yb-doped ${\mathrm{Gd}}_2{\mathrm{O}}_3$ cubic crystal. This crystal was obtained by the flux method using an original borate-based solvent, which was particularly well suited to the growth of rare earth sesquioxide crystals at half the working temperature of classical growth techniques. This flux method is a very interesting alternative for the production of laser sesquioxide crystals, not only because it provides access to new matrices of the cubic polymorph, but also because it permits high ${\mathrm{Yb}}^{3+}$-doping levels for these crystals. The first laser results of two highly ${\mathrm{Yb}}^{3+}$-doped sesquioxides, namely ${\mathrm{Gd}}_2{\mathrm{O}}_3$ and ${\mathrm{Y}}_2{\mathrm{O}}_3$, grown by this flux method are presented here, including the Ti:sapphire and diode pumping configurations. Laser efficiencies and emission spectra for these two crystals were studied and compared.

The influence of erbium ion concentration on the optical properties of BaF₂:ErF₃ crystals was investigated. Four ErF₃ concentration (0.05, 0.08, 0.15 and 0.5 mol% ErF₃)-doped BaF₂ crystals were obtained using the Bridgman technique. Room temperature optical absorption in the 250–850 nm spectral range was measured, and the photoluminescence (PL) and decay times were also investigated. The Judd–Ofelt (JO) approximation was used, taking into account four absorption peaks (at 377, 519, 653 and 802 nm). The JO intensity parameters, Ω_t (t = 2, 4, 6), were calculated. The influence of the ErF₃ concentration on the JO parameters, branching ratio, radiative transition probability and radiative lifetime were studied. The obtained results were compared with measured values and with those reported in the literature. Under excitation at 380 nm, the well-known green (539 nm) and red (668 nm) emissions were obtained. The calculated and experimental radiative lifetimes were in millisecond range for green and red emissions. The intensity of the PL spectra varied with the Er³⁺ ion concentration. The emission intensity increased linearly or exponentially, depending on the ErF₃ concentration. Under excitation at 290 nm, separate to the green and red emissions, a new UV emission band (at 321 nm) was obtained. Other research has not reported the UV emission or the influence of ErF₃ concentration on emission behavior.