Magnetic susceptibility as a function of temperature (4–250K) and EPR spectra at room temperature were studied for thermoluminescence detectors (TLD) CaF2:Mn with either stored dose information or cleaned dose by annealing. No essential variations of Mn2+ number in detectors were found due to dose storage; however, the exchange interactions between manganese ions are observed as deviations from Curie–Weiss law. These deviations are removed when samples are irradiated with high doses (250–500Gy) and appear again after dose annealing. The effect is regarded as indirect evidence of trapped exciton formation in the close vicinity of Mn2+ impurity, with the exchange interaction being destroyed by fluorine displacement from regular lattice position. The unusually high stability of trapped impurity excitons is explained by partial relaxation of lattice distortion caused by substitution of Ca2+ with a smaller Mn2+.