Spectroscopy of Tm3+-doped CaF2 waveguiding thin films grown by Liquid Phase Epitaxy

Thulium-doped calcium fluoride (Tm:CaF2) single-crystalline films are grown on (100)-oriented undoped bulk CaF2 substrates by Liquid Phase Epitaxy (LPE) using LiF as a solvent. Their spectroscopic properties are studied in details. For similar to 2 at.% Tm-doped films, the active ions are predominantly isolated and are located in oxygen assisted trigonal sites, C-3v(T-2). With increasing the Tm doping level, ion clustering is promoted but it is slowed down as compared to bulk crystals. For similar to 6 at.% Tm-doped films, the majority of active ions form clusters resulting in a "glassy-like" spectroscopic behavior (smooth and broad spectral bands). For such layers, the maximum stimulated-emission cross-section for the F-3(4) -> H-3(6) transition is 0.14 x 10(-20) cm(2) at 1856 nm, the luminescence lifetime of the F-3(4) state is 21.70 ms and the emission bandwidth exceeds 180 nm. The transition probabilities of Tm3+ ions are determined using the Judd-Ofelt theory. The waveguiding properties of the Tm: CaF2 films are confirmed. Highly-doped Tm:CaF2 epitaxial films are promising for waveguide lasers at similar to 2 mu m.