Sesquioxides are outstanding host materials for rare-earth doped laser gain media. Unfortunately, their very high melting points make it challenging for them to be fabricated in high quality. Recently, we demonstrated that some mixed sesquioxides exhibit significantly reduced melting temperatures compared to their constituents. This enables their growth by the established Czochralski method yielding rare-earth doped mixed sesquioxides of high optical quality. Due to their inhomogeneously broadened gain spectra caused by the intrinsic disorder, mixed sesquioxides are very promising for the generation and amplification of ultrashort pulses. To envisage the potential of this emerging class of gain materials, this paper reviews the spectroscopic as well as continuous wave and pulsed laser properties of crystalline and ceramic rare-earth doped mixed cubic sesquioxides of the form (Scx,Luy,Yz)2O3 with x + y + z = 1.

Cubic rare-earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large-size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3–Sc2O3–Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1 µm range.

Stimulated-emission cross-sections for the 4I11/2→4I13/2 and 4I13/2→4I15/2 transitions of Er3+ ions in three cubic sesquioxides Y2O3, Lu2O3 and Sc2O3 are revised. The transition probabilities in emission are determined using the Judd-Ofelt theory and lifetime studies.

We report on a detailed revision of the spectroscopic properties of Er3+ ions in the cubic sesquioxide host crystals R2O3 (R = Y, Lu and Sc). The 4f-4f transition probabilities are calculated by applying a modified Judd-Ofelt theory accounting for configuration interaction based on the measured absorption spectra. The stimulated-emission cross-sections for the 4I11/2 → 4I13/2 (at ∼2.8 µm) and 4I13/2 → 4I15/2 (at ∼1.6 µm) transitions of Er3+ ions are determined and the luminescence dynamics from the 4I11/2 and 4I13/2 manifolds are studied at different temperatures. It is found that the luminescence lifetime of the 4I11/2 state strongly depends on the host-forming R3+ cation even at low temperatures due to a non-negligible non-radiative multiphonon decay channel. Er:Y2O3 exhibits the lowest phonon energies and consequently the longest 4I11/2 luminescence lifetimes. A disagreement between the absorption and emission probabilities for the 4I15/2 ↔ 4I11/2 transition of Er3+ ions is observed at room temperature and explained considering the distribution of Er3+ ions over two non-equivalent crystallographic sites, C2 and C3i.

We represent the multi‐band's laser media as example principle possibility of application of laser diodes for radiation excitation in visible and UV spectrum ranges. Possibility of excitation luminescence in region from 230 to 650 nm from the high laying 4f and 5d states of ions Pr3+ and Ce3+ in active media of BaY2F8:(Yb3+, Pr3+, Ce3+), excited by radiation of 960 nm, 840‐808 nm and 405 nm laser diodes is considered. Spectra of the realized visible luminescence are shown at one‐wave and multi‐wave pumps by infrared (IR) laser diodes. The up‐conversion schemes of excitation the 5d‐UV luminescence from Pr3+ and Ce3+ by laser diodes is reported. Possibility of the realization 5d‐ luminescence from Pr3+ and Ce3 ions is discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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We report on the Czochralski growth, spectroscopy, and laser operation of Er- and Yb-doped mixed sesquioxide crystals. Er(7 at.%):(Y,Sc)2O3 enables 19% slope efficiency at 2.7 µm, Yb(0.4 at.%):(Y,Sc)2O3 yields 87% at 1.04 µm.

We report on observation of up‐converted ultraviolet (UV) luminescence due to 5d–4f transitions from Pr3+ and Ce3+ ions doped into Ba(Y,Yb)2F8single crystals under excitation by IR laser diodes. The dependence of population of crucial intermediate 3P0 level Pr3 + from absorbed energy is discussed. The point of view of adaptation of the active medium in structure and concentration of activators to developed up‐conversion scheme is considered (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)