The thermoluminescent (TL) response to ultraviolet irradiation of CaF2:Tm phosphor is affected by pre-irradiation high-temperature treatment. The experimental results indicate that the maximum intrinsic TL output is about 2000 times higher for 1000 degrees C treatment than when not treated. TL stability for this phosphor occurs when the optimum temperature range and time are 800 degrees to 900 degrees C and 1 h. However, the intrinsic sensitivity is only about 50 times higher than with no treatment, which limits the application of this phosphor as a personal UV dosimeter.