A heavy metal oxide glass selected from germanate, tellurite and bismuth oxide glasses provides a host for highly efficient Thulium doped 2 .mu.m oxide glass and fiber lasers. The concentration of Thulium ions is high enough that energy transferred by the phenomenon of cross-relaxation will enhance laser emission at 2 .mu.m and suppress emission at 1.5 .mu.m so that 2 .mu.m emission is dominant.