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Sensitisation of the Tm3+-ion luminescence by Cr4+ ions in continuous 2-μm lasing in a YAG : Tm3+:Cr4+:Ca2+ crystal

Continuous lasing in the 2 μm wavelength range was achieved in a YAG : Tm3+:Cr4+:Ca2+ crystal as a result of a transition in the Tm3+ ion. The crystal was pumped longitudinally with radiation from a cw Nd laser at the wavelength of 1.06 μm, which was within the absorption band of the tetrahedrally coordinated Cr4+ ion. Quantum efficiency of the transfer process was estimated on the assumption that the excitation energy was transferred nonradiatively from the Cr4+ to the Tm3+ ions. The Cr4+ ions were used for the first time as the sensitisers of the luminescence of the active centres in a solid-state laser.