Photoluminescence of (Ba1−xEux)Si6N8O (0.005≤x≤0.2) phosphors

Eu2+-doped BaSi6N8O phosphors (Ba1−xEuxSi6N8O, 0.005≤x≤0.2) were synthesized by gas-pressure sintering of the powder mixture of BaCO3, Si3N4, and Eu2O3 at 1750 °C under 0.5 MPa N2. The fired powder consists of a major BaSi6N8O phase and a trace amount of impurity phases. The structural result of the BaSi6N8O powder, refined by the Rietveld method, agrees well with that of single crystals. A wide blue luminescence band peaking at about 500 nm is observed in BaSi6N8O:Eu2+, upon excitation with the ultraviolet light of 310 nm. Although Eu is covalently bonded to six nearest neighbor nitrogen atoms, the luminescence of Eu2+ is not significantly redshifted but shows a very narrow excitation spectrum at high energies. The origin of the short-wavelength luminescence is mainly ascribed to a small crystal-field splitting as a result of extremely long distances between europium and nitrogen ligands in BaSi6N8O:Eu2+.