Has been engaged in developing phosphors/ nanophosphors by different synthesis routes for applications in stratogic display devices. As luminescence quantum efficiency of phosphors play a very important role in improving the efficacy of display devices, a new experimental facility using an integrating sphere has been established for absolute quantum efficiency measurement of phosphors. The group has been working on “Synthesis of phosphors for Plasma Display Panels (PDP)” in association with M/s SAMTEL India Ltd, Gaziabad on a collaborative project on “Development of next generation Plasma Display Panel Technology and 50” High Definition (HD) TV Prototype” under NMITLI Program. Red, Green and Blue (RGB) PDP Phosphors have been developed. The developed phosphors were tested under vacuum ultraviolet (VUV) excitation using a VUV Xenon lamp and also under UV excitation attached to Luminescence Spectrometer available at NPL. Quantum efficiency of developed phosphors were measured with our new experimental facility and compared with commercial PDP phosphors used by SAMTEL Colour Lab Ltd. PDP phosphors developed at NPL have high quantum efficiency almost at par with commercial phosphors. Developed RGB phosphors and their luminescence emission spectra under VUV excitation (172 nm) are shown in Fig. 4.1.

New down conversion phosphors/ nanophosphors have been explored and developed for solid state lighting in conjunction with blue/ near UV LED. The main phosphors developed for this purpose are YAG:Ce codoped with Praseodymium for successful enhancement of red part of resultant white LED spectrum, SrAl2O4 doped with Praseodymium and SrAl12O19 doped with various rare earth activators for excitation by blue LED light. Binary & ternary nanophosphor powder and thin film of ZnO/ ZnMgO were developed which were excitable by near UV (350nm) light (commercial UV-LED) and can produce broadband white emission (Fig. 4.2). Optimum synthesis parameters for producing reliable and high brightness ZnO and ZnO1–xSx nanophosphors that could be excited efficiently in the near UV region (between 340-480 nm) were identified and established.

Synthesis of ZnO nanophosphor doped with alkali, alkaline earth and transition metal atoms through different precursor routes was taken up in an effort to obtain p-type conductivity in ZnO which is very difficult to achieve. p-type conduction in alkali doped ZnO and Mg doped ZnO has been achieved (Fig. 4.3). In addition, synthesis of strong green emitting ZnO phosphor, improvements in emission efficiency by doping Mm (misch-metal), Sb and surface passivation of ZnO nanophosphor by capping with inorganic as well as organic material was done for possible electroluminescent, biological and pharmaceutical applications. Production process for high yield ZnO nanorods/tetrapods/nanostructures was optimized for fabrication of futuristic field emission devices. Band gap engineering of ternary ZnO1–xSx nanophosphor system was successfully carried out using High Pressure Autoclave attached with a high pressure liquid chromatography pump.