IR-visible upconversion and thermal effects in Pr3+/Yb3+-codoped Ga2O3 : La2S3 chalcogenide glasses

IR-visible upconversion fluorescence spectroscopy and thermal effects in pr (3+)/Yb3+-codoped Ga2O3:La2S3 chalcogenide glasses excited at 1.064 mum is reported. Intense visible upconversion emission in the wavelength region of 480-680 nm peaked around 500, 550, 620 and 660 nm is observed. Upconversio n excitation of the Pr3+ excited-state visible emitting levels is achieved by st combination of phonon-assisted absorption, energy-transfer and phonon -assisted excited-state absorption processes. A threefold upconversion emis sion enhancement induced by thermal effects when the codoped sample was hea ted in the temperature range of 20-200 degreesC is demonstrated. The therma l-induced enhancement is attributed to a multiphonon-assisted anti-Stokes p rocess which takes place in the excitation of the ytterbium and excited-sta te absorption of the praseodymium. The thermal effect is modelled by conven tional rate equations considering temperature-dependent effective absorptio n cross-sections for the F-2(7/2)-F-2(5/2) ytterbium transition and (1)G(4) -P-3(0) praseadymium excited-state absorption, and it is shown to agree ver y well with experimental results. Frequency upconversion in singly Pr3+-dop ed samples pumped at 836 nm and 1.064 mum in a two-beam configuration is al so examined.