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

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