Eu3+-doped CaF2 nanocrystals in sol–gel derived glass–ceramics

Glass–ceramics containing Eu3+-doped CaF2 nanocrystals of about 16 nm size have been made using the controlled crystallization at higher temperatures of the Eu3+-doped CaF2–SiO2 xerogels. In the glass–ceramic material the Eu3+ ions are embedded in both silica network and in the non-centrosymmetric sites of the CaF2 nanocrystals structure. Lower phonon energy of CaF2 and the dehydratation processes reduce the probability of non-radiative de-excitations and as a result a luminescence enhancement and an increase of the PL lifetime is observed. Eu-doping modifies the traps distribution within the glass–ceramics and as a result an additional broad thermoluminescence peak at about 380 °C was observed. The peak was assigned to the recombination of the electrons thermal released from the Eu3+-related traps in the glass matrix and in the CaF2 nanocrystals.

Research highlights
► Annealing of Eu3+-doped SiO2–CaF2 xerogel induces the crystallization of CaF2 nanocrystals.
► Eu3+ ions are embedded in the glass and in non-centrosymmetric sites of the CaF2 nanocrystals.
► Luminescence enhancement and an increase of the PL lifetime was observed in the glass-ceramics.
► Recombination of Eu3+ related electron traps gives rise to thermoluminescence.