Europium (II)-Doped CaF 2 Nanocrystals in Sol-Gel Derived Glass-Ceramic: Luminescence and EPR Spectroscopy Investigations.

The remarkable properties of Eu 2+ -activated phosphors, related to the broad and intense luminescence of Eu 2+ ions, showed a high potential for a wide range of optical-related applications. Oxy-fluoride glass-ceramic containing Europium (II)-doped CaF 2 nanocrystals embedded in silica matrix were produced in two steps: glass-ceramization in air at 800° with Eu 3+ -doped CaF 2 nanocrystals embedded followed by Eu 3+ to Eu 2+ reduction during annealing in reducing atmosphere. The broad, blue luminescence band at 425 nm and with the long, weak tail in the visible range is assigned to the d → f type transition of the Eu 2+ located inside the CaF 2 nanocrystals in substitutional and perturbed sites, respectively; the photoluminescence quantum yield was about 0.76. The X-ray photoelectron spectroscopy and Electron paramagnetic spectroscopy confirmed the presence of Eu 2+ inside the CaF 2 nanocrystals. Thermoluminescence curves recorded after X-ray irradiation of un-doped and Eu 2+ -doped glass-ceramics showed a single dominant glow peak at 85 °C related to the recombination between F centers and Eu 2+ related hole within the CaF 2 nanocrystals. The applicability of the procedure can be tested to obtain an oxy-fluoride glass-ceramic doped with other divalent ions such as Sm 2+ , Yb 2+ , as nanophosphors for radiation detector or photonics-related applications.