Narrow-band red phosphors of high colour purity based on Eu3+-activated apatite-type Gd9.33(SiO4)6O2

A series of new red phosphors based on apatite-type gadolinium silicate host, Gd9.33−xEux(SiO4)6O2 (0.03 < x < 1.87), have been synthesised and analysed. The phosphors show excellent chemical and thermal stability, losing only 10% of their emission intensity at 150 °C (working LED temperature) relative to that at room temperature through the electric dipole–dipole interaction. They exhibit efficient Eu3+ narrow-band red emission (quantum yield up to 75%; full-width at half-maximum (FWHM) = 7 nm; CIE colour coordinates x = 0.65, y = 0.35) of exceptional colour purity (94.2%), and the host can be heavily doped with Eu3+ (up to 10 at%) without concentration quenching of the emission. Variable-temperature powder X-ray diffraction, photoluminescence spectroscopy and Judd–Ofelt analysis of the phosphors’ radiative properties reveal the favourable influence of the structural properties of the apatite-type host on the efficiency and thermal stability of the Eu3+-activated Gd9.33(SiO4)6O2 emission.