Energy transfer and sensitization blue-upconversion in Tm3+/Yb3+co-doped tellurite glasses

This paper reports on energy transfer and infrared-to-blue upconversion of Tm3+/Yb3+co-doped tellurite glasses upon excitation with 800 and 980 nm laser diode (LD). The glasses were prepared by the conventional melting method. Their optical spectroscopic properties, direct and indirect sensitization upconversion have been discussed. An intense 475 nm blue upconversion was clearly observed upon excitation of a 980 nm LD. It is interesting to note that the peaks of the blue upconversion at 475 nm changed first to 452 nm, then to 468 nm with increasing Yb-doping concentration upon excitation of a 800 nm LD, which might be due to the indirect sensitization upconversion. To our knowledge, a similar result has not been reported before. The mechanism involved has been explained.