YAl3(BO3)4:Yb&Tm a nonlinear crystal: Up- and down-conversion phenomena and excited state relaxations

Abstract Excitation and relaxation phenomena within the Yb 3+ –Tm 3+ system in the YAl 3 (BO 3 ) 4 (YAB) crystal were investigated upon continuous wave and short pulse excitation at 975 and 660 nm. With the 975 nm excitation, an unusually intense luminescence from 3 H 4 , and a considerably weaker one from 1 G 4 of Tm 3+ have been observed at 800 (IR) and 480 nm (VIS), respectively. The intensity ratio of the IR to VIS up-converted emissions is strongly affected by dopant concentrations. The dependence of the anti-Stokes emission intensities on the excitation power implies a two-step excitation mechanism of the 3 H 4 luminescence and a three-step excitation of the 1 G 4 one. Down-converted emission from the 2 F 5/2 ytterbium level has been observed following the 660 nm excitation of the 3 F 2 thulium state. The optical and kinetics results provided that energy transfer processes are responsibly for the up- and down-conversion phenomena. Even though the Yb 3+ –Tm 3+ energetic system is far from resonance, the energy transfer processes are surprisingly efficient in the YAB host. A high intensity of the up-converted emission at 800 nm may offer a laser potential.