INFRARED TO VISIBLE LUMINESCENCE UPCONVERSION BY Yb³⁺ RE³⁺ ENERGY TRANSFER IN β'' -ALUMINA (RE³⁺=Er³⁺, Ho³⁺, Tm³⁺)

Abstract
Beta"-alumina crystals containing mixed Yb³⁺-RE³⁺(RE³⁺=Er³⁺,Ho³⁺,Tm³⁺) pairs are synthesized by ion exchange techniques. Under a 970 nm excitation from a C.W. Ti-sapphire laser, a fluorescence is observed in the visible range with the three codoped samples. This work presents the efficiency results in the β''-alumina matrix. The mechanism and upconversion efficiencies for the Yb³⁺-Er³⁺ systems are discussed as well as the choice of the host for the upconversion mechanisms. A good matrix should have the capacity to be doped with a high concentration of rare earth ions and to have low phonon energies to discourage non-radiative and to encourage radiative processes.