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

Several well-known phosphors compositions based on rare earth orthoborates, with the general formula LnBO3 with Ln = [Y0.95−yGdyEu0.05] or [Y0.95−yGdyTb0.05], and the cubic oxide (Y0.96Eu0.04)2O3 have been synthesized by spray-pyrolysis (SP) and additional thermal treatments. Samples with the unique hexagonal YBO3 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 Y2O3:Eu3+ 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 Eu3+ emission intensities are at least 50% higher for SP yttrium borates than for SP yttrium oxide; the decay times τ10 are 13 ± 1 msec and 4.6 ± 0.4 msec, respectively. Up to 80% efficiency of a commercial green phosphor (Zn2SiO4:Mn2+), and τ10 = 15 ± 1 msec were easily achieved in spray pyrolysed Tb3+ 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.