Wide‐bandgap materials doped with rare‐earth ions are currently of great interest as new vacuum ultraviolet (VUV) phosphors for lighting and displays. This paper reports the development of a highly sensitive green phosphor, CaSO4:Tb,Na, which exhibits a quantum efficiency higher than 100 % by exploiting the energy‐transfer mechanism from anion excitons to the activator ions, Tb3+. The VUV excitation spectra of CaSO4:Tb3+ with Na+ as a charge compensator show two prominent excitation bands at 147 and 216 nm. The former band is attributed to the charge‐transfer excitations within SO42– complexes while the latter was assigned to the 4f8 → 4f75d transitions on Tb3+. The energy‐transfer mechanism from anion excitons to Tb3+ strongly raises the possibility of two‐photon emission via a second‐order down‐conversion under the VUV excitation, which is basically a new approach in the goal of achieving a quantum‐splitting phosphor.
New Recipes for rare earth doped CaSO 4 luminescence phosphors which give high photoluminescence efficiency combined with high thermal stability desired for noval display applications are described. The influence of cooling rate, thermal treatments and water washing as well as crystal size and morphology on the luminescence efficiency are described. While a modified co-precipitation technique was found best suited for preparing thermostimulated luminescence phosphors required for radiation dosimetry, those made by solid state diffusion reactions at high temperatures were found best suited to achieve the high photoluminescence efficiency required for lighting and display applications.www.pss-a.com fect phosphor surface is required. This is optimally achieved with the production of small (2-4 µm) spherical grains at the preparation stage itself without the need to grind larger grains. Another important requirement of display phosphors is the stability of luminescence efficiency against high temperature treatments usually adopted during the baking process of the display panel used for binder burn-off. This paper describes briefly the CaSO 4 phosphors successfully developed by the authors for the first time using different techniques with high fluorescence efficiency, thermal stability and the desired crystal morphology. The potential application of these phosphors for novel display devices such as PDP, fluorescent lamps, liquid crystal display (LCD) backlight and light emitting diodes (LED) will be highlighted A new co-precipitation technique which yields high TSL sensitivity with the desired glow curve structure for applications in radiation dosimetry will also be presented.
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