Toward a new generation of white phosphors for solid state lighting using glassy yttrium aluminoborates†
We present a new family of highly emissive white phosphors. These phosphors are based on original glassy yttrium aluminoborates (g-YAB) compositions, obtained at low temperatures without any melting, from non-toxic and low cost precursors through the generic polymeric precursor method. Their photoluminescence (PL) arises from structural defects, whose energy levels are widely extended within the large bandgap of these materials. One of the main objectives of this work, is to enhance the point defect concentrations by accurately controlling the powder annealing (temperature and atmosphere) in order to generate intense and broadband PL. Moreover, these g-YAB powders exhibit excellent thermal and chemical stabilities and tunable PL properties, from bluish to warm white emissions, by simply adjusting the annealing temperatures. We determined the internal quantum yields of g-YAB powders using near ultraviolet excitations, which reached values above 90%. We quantified the relative amounts of point defects by electronic paramagnetic resonance and their distribution within the bandgap by means of thermally stimulated luminescence and we directly correlated this defect density to the PL properties. Finally, based on these promising lighting properties, a prototype was firstly developed to estimate the lighting performances of this new g-YAB phosphors family.