IR-visible upconversion and thermal effects in Pr3+/Yb3+-codoped Ga2O3:La2S3chalcogenide glasses

IR-visible upconversion fluorescence spectroscopy and thermal effects in Pr 3+ /Yb 3+ -codoped Ga 2 O 3 :La 2 S 3 chalcogenide glasses excited at 1.064 µm is reported. Intense visible upconversion emission in the wavelength region of 480-680 nm peaked around 500, 550, 620 and 660 nm is observed. Upconversion excitation of the Pr 3+ excited-state visible emitting levels is achieved by a combination of phonon-assisted absorption, energy-transfer and phonon-assisted excited-state absorption processes. A threefold upconversion emission enhancement induced by thermal effects when the codoped sample was heated in the temperature range of 20-200 °C is demonstrated. The thermal-induced enhancement is attributed to a multiphonon-assisted anti-Stokes process which takes place in the excitation of the ytterbium and excited-state absorption of the praseodymium. The thermal effect is modelled by conventional rate equations considering temperature-dependent effective absorption cross-sections for the 2 F 7/2 - 2 F 5/2 ytterbium transition and 1 G 4 - 3 P 0 praseodymium excited-state absorption, and it is shown to agree very well with experimental results. Frequency upconversion in singly Pr 3+ -doped samples pumped at 836 nm and 1.064 µm in a two-beam configuration is also examined.