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Oxide Phosphors and Thin Film Electroluminescent Devices

Thin film electroluminescent (TFEL) devices are one of the upcoming and sought after Flat Panel Displays (FPD) owing to its ruggedness and solid state nature. Although the conventional TFEL devices are mainly based on sulphide phosphors (ZnS, SrS etc), progressive research has been accelerated over the last decade towards improving oxide phosphors for flat panel display applications over commercially available sulphide phosphors. Their ability to serve as potential substitutes arise from their excellent stability in vacuum under irradiation of electrons and emission of fewer harmful gases on electron bombardment. These phosphors are also widely investigated as candidates for vacuum fluorescent displays, electroluminescent displays and field emission displays.

Several oxide phosphor hosts like ZnGa2O4, Zn2GeO4, Zn2SiO4, Y2O3 etc are being extensively studied in our lab. These inorganic materials are made to luminesce in the red/green/ yellowish-white regions of the visible spectrum by suitably doping with transition metals like Mn2+ and rare-earths like Eu3+ and Dy3+. Works have been carried out in the bulk phosphors as well as in thin films grown by RF magnetron sputtering/Pulsed Laser Deposition (PLD) technique.

The high crystallization temperature of oxide phosphors necessitates high temperature post-deposition annealing for the realization of oxide phosphor based TFEL devices. Thick Dielectric Electroluminescent (TDEL) devices fabricated on ceramic substrates have been reported to exhibit high luminance after post deposition annealing at temperatures as high as 1000oC. The deposition of these materials on low temperature substrates like glass was therefore investigated. Fabrication of ACTFEL devices based on ZnGa2O4:Mn2+ and Zn2GeO4:Mn2+ active layers on glass substrates in the conventional MISIM structure are also being accomplished.  

Sulphide Phosphors and Thin Film Electroluminescent Devices

Recent advances with SrS:Ce and SrS:Cu phosphors have determined that they are extremely important phosphors for the realization of full colour ACTFEL displays. Excellent charge injection and polycrystallinity at low processing temperatures make the sulfides phosphors unique among phosphor materials. We fabricate EL devices based on strontium sulphide.