Phosphor powders elaborated by spray-pyrolysis: Characterizations and possible applications

Several well-known phosphors compositions based on rare earth orthoborates, with the general formula LnBO 3 with Ln = [Y 0.95− y Gd y Eu 0.05] or [Y 0.95− y Gd y Tb 0.05], and the cubic oxide (Y 0.96Eu 0.04) 2O 3 have been synthesized by spray-pyrolysis (SP) and additional thermal treatments. Samples with the unique hexagonal YBO 3 type phase have been obtained. The particles are spherical, the average diameter is around 2 μm, with a relatively narrow spreading. The borate spheres are not dense: porosities are observed, but do not exhibit the core-shell aspect observed for Y 2O 3:Eu 3+ spheres. The emission spectra, the relative intensities, and the transient characteristics of phosphors under VUV excitation by a pure Xe gas discharge have been measured in a specially developed experimental set-up. The integrated Eu 3+ emission intensities are at least 50% higher for SP yttrium borates than for SP yttrium oxide; the decay times τ 10 are 13 ± 1 msec and 4.6 ± 0.4 msec, respectively. Up to 80% efficiency of a commercial green phosphor (Zn 2SiO 4:Mn 2+), and τ 10 = 15 ± 1 msec were easily achieved in spray pyrolysed Tb 3+ yttrium borates. The Gd/Y substitution and the annealing temperature have a very weak effect on the europium and the terbium luminescence efficiencies and decay times.