Excitation of the thulium /sup 1/G/sub 4/ level

Summary form only given. Infrared pumped upconversion lasers in the visible wavelengths range are of great interest. We have found an excitation scheme for diode pumping laser action has not yet been reached but we have measured spectral properties of crystal and glass samples with various thulium concentration in the range from 300 nm to 2300 nm. Ytterbium is needed sensitise the excited state absorption and to enable efficient diode pumping at 940 nm or 790 nm. Lifetimes of the /sup 1/G/sub 4/ level of thulium are presented for several host materials.