Enhancement of encaged electron concentration by Sr2+ doping and improvement of Gd3+ emission through controlling encaged anions in conductive C12A7 phosphors

Abstract

Conductive C12A7:0.1%Gd³⁺,y%Sr²⁺ powders with different Sr²⁺ doping concentrations have been prepared in a H₂ atmosphere by a solid state method in combination with subsequent UV-irradiation. The encaged electron concentration could be modulated through tuning Sr²⁺ doping and its maximum value reaches 2.3 × 10¹⁹ cm⁻³. This is attributed to the competition between enhanced uptake and the release of the encaged anions during their formation and diffusion processes and the suppression of encaged electrons generation due to the increased encaged OH⁻ anions and the decreased encaged O²⁻ anions. Although there exists encaged electrons and different encaged anions (O²⁻, H⁻ and OH⁻) in C12A7 conductive powders prepared through the hydrogen route, a dominant local environment around Gd³⁺ could be observed using electron spin resonance (ESR) detection. It can be ascribed to the stronger coupling of the encaged OH⁻ to the framework of C12A7 than those of the encaged electrons, O²⁻ and H⁻ anions. In addition, emission of Gd³⁺ ions is enhanced under UV or low voltage electron beam excitation and a new local environment around Gd³⁺ ions appears through the thermal annealing in air because of the decrease of the encaged OH⁻ anions and the increase of the encaged O²⁻ anions. Our results suggested that Sr²⁺ doping in combination with thermal annealing in air is an effective strategy for increasing the conductive performance and enhancing the emission of rare earth ions doped into C12A7 conductive phosphors for low-voltage field emission displays (FEDs).