Luminescent behaviour of SrF2 and CaF2 crystals doped with Eu ions under different annealing temperatures

The photoluminescent (PL) properties of europium (Eu) doped SrF2 and CaF2 nanoparticles have been investigated after annealed in an Ar/H2 atmosphere at different temperatures for possible down-conversion applications in solar cells. PL investigations revealed that the Eu doped samples exhibited emission from both Eu2+ and Eu3+ ions. The emission spectrum’s shape of the Eu2+ doped SrF2 sample stayed unchanged, unlike the Eu2+ doped CaF2 sample. Temperature treatments significantly affected the Eu3+ emission. A complete reduction of Eu3+ to Eu2+ occurred during heating under H2 atmosphere. Degradation of the Eu2+ emission intensity occurred during prolonged laser irradiation of the annealed SrF2 as-prepared samples, but it was stable at 800 °C annealing temperature. These results demonstrated that temperature treatment destroyed the surface trap centers and enhanced the photoemission stability of the Eu2+. [Display omitted] •Nanocrystalline alkaline earth fluoride materials influence the Eu ion emission stability.•Annealing treatment enhanced the stability of Eu emission.•Existence of impurities in a fluoride material alters the Eu emission characteristics.