Single-phase white-emitting phosphors based on apatite-type gadolinium silicate, Gd9.33(SiO4)6O2 doped with Dy3+, Eu3+ and Tb3+

Abstract

Two series of new apatite-type silicate materials were synthesised and characterised with the aim of achieving white light emission from single-phase phosphors. The Gd_9.33(SiO₄)₆O₂ host was doped systematically with Dy³⁺, Tb³⁺ and Eu³⁺ to tune the emission to the white light region. Eight new phosphors with emission very near the ideal white light point are reported. The best properties are found for the 0.5%Tb, 0.03%Eu co-doped Gd_9.33(SiO₄)₆O₂, with colour coordinates (0.340, 0.341) and a correlated colour temperature of 5190 K, corresponding to the white light region. The temporal decay of emission from the doped ions was measured following pulsed excitation of the Gd³⁺ host. An evaluation of energy transfer and quenching effects in the phosphors has been made based on the lifetimes so obtained. In particular, a comparison of the Eu³⁺ lifetimes in the Dy,Eu co-doped phosphors with those in the Tb,Eu-containing materials suggests quenching of the ⁵D₀ excited state of Eu³⁺ by the Dy³⁺ ions. These observations imply that the combination of Eu³⁺ and Dy³⁺ ions may not provide optimal efficiencies in phosphors, and that the combination of Eu³⁺ and Tb³⁺ is likely to be superior for optimising the emission properties.