The upconversion of infrared radiation into green and red fluorescence has been studied for Er3+ and Yb3+ ions in BaF2/ThF4 fluoride glass over a wide temperature range and several dopant concentrations. At room temperature an upconversion efficiency of 3.3×10−5 has been obtained for the green emission from the glass with 1 mol % ErF3 and 19 mol % YbF3 pumped by 973-nm radiation with intensity of 16.5 mW/cm2. For an absorbed intensity of 10 W/cm2 the efficiency for green upconversion emission is predicted to be 2%. Radiative transition rates for the excited states of Er3+ were calculated using Judd–Ofelt theory and intensity parameters obtained from measured integrated absorption coefficients. The calculated values of the multiphonon relaxation and the upconversion fluorescence intensity, obtained from the rate equation model of Wright, are discussed in light of the experimental results.

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Enhancement of optical nonlinearity of heavymetal oxide glasses by replacing lead and bismuth with thallium Appl.The upconversion of infrared radiation to shorter wavelengths by Er3 + ions in heavy-metal fluoride glasses, some doped with Yb 3 + , has been studied over a wide intensity range and for various excitation wavelengths. The upconversion efficiency measured at room temperature varies linearly or quadratically with intensity and saturates at 100 W/cm* or higher, depending on emission wavelength. For 4 mol % ErF, in BaF,/ThF,, the 41, ,,* to 41,,,2 transition is over 10% efficient for 400 W/cm* of absorbed 1.5pm power, i.e., for 41,,,, to 41,,,, excitation. A rate equation model and Judd-Gfelt analysis of data for the glasses doped with just Er" + provide an understanding of the upconversion process while yielding values for Er" + energytransfer rates and excited-state populations. These results could be used to develop glasses for lasing and as infrared optical detectors.

If infrared light can be efficiently changed to visible light it would have important implications for optical detection and display devices. In this paper the efficiency of the two-photon upconversion process between Yb3+ and Tm3+ ions in BaF2/ThF4 heavy metal fluoride glass is investigated as a function of Tm3+ concentration and temperature. It is found that for the concentration of 0.05-mol % TmF3 and a projected incident infrared intensity of 1 W/cm2, the projected efficiency at 300 K would be 1.2%.