Emission Characteristics of Eu2+ and Eu3+ under X-Ray and Alpha Irradiation in Eu-Doped CaF2 Crystals

Abstract Calcium fluoride crystals doped with europium (CaF2:Eu) have long been used as conventional inorganic scintillators. Their luminescence is primarily attributed to emission from Eu2+ centers, typically around 420 nm. However, it has been reported that increasing the Eu concentration leads to enhanced Eu3+ emission in the wavelength range of 590-700 nm. In this study, CaF2:Eu:Eu crystals with various Eu concentrations (0, 0.3, 1, 2, 3, and 5 mol%) were grown and irradiated with both X-rays and alpha-particles from a 241Am source. Radioluminescence spectra were measured for each excitation condition and compared across samples.The results clearly show that the relative contribution of Eu3+ emission is approximately twice as high under alpha-particle irradiation compared to X-ray excitation. This enhancement was found to be consistent for Eu concentrations above 1%, and independent of the crystal thickness or geometry. To the best of our knowledge, this is the first report demonstrating that the emission intensity ratio of Eu2+/Eu3+ centers in CaF2:Eu scintillators depends on the type of incident radiation.