Cr4+ ions as a new efficient sensitiser of laser materials for the wavelength range 1.5–3 μm, activated with Er3+, Tm3+, Ho3+, and Dy3+ ions

A technique has been developed in which Cr⁴⁺ ions are used for the direct sensitisation of the luminescence from the upper laser-active levels of the following rare-earth ions: Er³⁺ (⁴I_13/2), Tm³⁺ (³H₄), Ho³⁺ (⁵I₇), Dy³⁺ (⁶H_13/2). Energy is transferred directly from Cr⁴⁺ to these levels. Crystals of YAG containing Cr³⁺ and Cr⁴⁺, as well as Er³⁺, Tm³⁺, Ho³⁺, and Dy³⁺ were grown. The microscopic constants and the quantum efficiencies of the Cr⁴⁺ → Er³⁺ and Cr⁴⁺ → Tm³⁺ energy transfer processes were determined.