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.