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The use of the green emission in Er3+-doped CaF2 crystals for thermometry application

We report here the use of the green upconversion emissions originating from the thermally coupled levels 2H11/2 and 4S3/2 of the Er3+ ion in CaF2:Er (0.01 at.%) for thermometry application in the range 303–423 K. The mechanism responsible for excitation of the green emitting levels is a sequential two-photon absorption process. The fluorescence intensity ratio (FIR) of the green upconversion emissions at wavelengths of about 519 and 551 nm is studied as a function of temperature in the range 303–423 K using a 634 nm tunable dye laser as an excitation source. It is found that the logarithm of the FIR varies linearly with the inverse of temperature. The gap between the two thermally coupled levels 4S3/2 and 2H11/2 was determined to be about 721 cm−1. This value is in good agreement with that found by spectroscopic investigations. The calibration curve is established, and the temperature is calculated.