Characterization of various Eu2+ sites in Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+ by high-pressure spectroscopy

Photoluminescence of Ba2SiO4 and Ca2SiO4 activated with Eu2+ was investigated at various temperatures (from 10 K to 300 K) and pressures (from ambient to 200 kbar). At ambient pressure and room temperature, under UV excitation both phosphors yielded a green emission band with maxima at 505 nm and 510 nm for Ba2SiO4 and Ca2SiO4, respectively. The energies of these bands depended on pressure; the pressure shifts were −12:55 cm−1/kbar for Ba2SiO4:Eu2+; and −5:59 cm−1/kbar for Ca2SiO4:Eu2+. In the case of Ca2SiO4:Eu2+, we observed additional broadband emission at lower energies with a maximum at 610 nm (orange band). The orange and green emission in Ca2SiO4:Eu2+ had different excitation spectra: the green band could be excited at wavelengths shorter than 470 nm, whereas the orange band — at wavelengths shorter than 520 nm. The pressure caused a red shift of orange emission of 7.83 cm−1/kbar. The emission peaked at 510 nm was attributed to the 4f65d→4f7(8S7=2) transition of Eu2+ in the β — Ca2SiO4:Eu2+ phase, whereas the emission peaked at 610 nm — to the γ — Ca2SiO4:Eu2+ phase. The emission of Ba2SiO4:Eu2+ peaked at 505 nm was attributed to the 4f65d→ 4f7(8S7/2) transition of Eu2+ in the β — Ba2SiO4 phase.