Upconversion emission enhancement induced by thermal effects in infrared excited Pr/sup 3+//Yb/sup 3+/-codoped Ga/sub 2/O/sub 3/:La/sub 2/S/sub 3/ chalcogenide glasses

Summary form only given. Thermally induced enhancement of infrared-to-visible frequency upconversion in Pr/sup 3+//Yb/sup 3+/-codoped chalcogenide glasses excited at 1.064 /spl mu/m is demonstrated. The Pr/sup 3+//Yb/sup 3+/-codoped 70%Ga/sub 2/O/sub 3/:30%La/sub 2/S/sub 3/ glass samples were excited at 1.064 /spl mu/m, and heated in the temperature range of 20 to 200/spl deg/C. For a fixed excitation power and temperature, the upconversion emission spectrum obtained from the sample is depicted. It presents three bands centered around 500, 546, and 650 nm corresponding to the /sup 3/P/sub 1/-/sup 3/H/sub 4/, /sup 3/P/sub 1/-/sup 3/H/sub 5/, and /sup 3/P/sub 0/-/sup 3/F/sub 2/ transitions, respectively. The temperature dependence of the fluorescence intensity was studied and the results revealed an upconversion efficiency enhancement of /spl times/3.5 in the temperature range of 20-130/spl deg/C. The behavior of the system is described by conventional rate equations for the pertinent Pr/sup 3+/-Yb/sup 3+/ energy-levels, including an effective temperature dependent absorption cross-section /spl sigma//sub d/(T)=/spl sigma//sub d//sup 0/F(T) for the Yb/sup 3+/-sensitizer, where /spl sigma//sub d//sup 0/ is the cross-section at resonance and F(T)=[exp(h/spl nu//sub phonon//k/sub B/T)-1]/sup -p/. The exponent p is the number of phonons involved in the sensitizer excitation. The population of the P/sup 3+/ excited-state emitting levels was accomplished through anti-Stokes multiphonon-assisted excitation of the Yb/sup 3+/ ions and subsequent energy-transfer to and excited-state absorption from the Pr/sup 3+/ ions.