| Popis: |
This chapter aims to explain the basic mechanism of phosphor materials and the luminescence behaviour of glasses doped with certain rare earth ions. It will also describe phosphor based white light emitting diodes and their significance. The photoluminescence properties of Ca3Y2Si3O12 doped with Ce3+, Tb3+ and Tb3+& Ce3+ co-doped phosphors prepared by the sol-gel method are presented. Photoluminescence (PL) spectra revealed a brighter and broader violet-blue colour emission from the Ce3+ (5d(2D) - 2F5/2,7/2) and an intense sharp green emission (545 nm) colour from the Tb3+ (5D4 -7F5) doped phosphors respectively. For Tb3+ and Ce3+ co-doped phosphors, a strong green emission (5D4-7F5) has been observed upon excitation with a UV wavelength (242nm). An energy transfer phenomenon from Ce3+ to Tb3+ was seen in these co-doped nanocrystalline phosphors. A dependency of the PL intensity on the doping concentration of Ce3+ was found, for a fixed concentration of Tb3+. The luminescent properties of the Ce3+ or Dy3+ singly doped and (Ce3+ & Dy3+) co-doped Ca3Y2Si3O12 novel phosphors are also reported. The Ce3+ doped phosphor showed a brighter /broader violet-blue colour emission (389nm), which is attributed to the parity and spin allowed 5d-4f transition. Photoluminescence spectra reveal that the white emission originated from the mixtures of two characteristic luminescence of Dy3+ ion, i.e. the 4F9/2-6H15/2 at 473 nm blue emission, and 4F9/2-6H13/2 at 580 nm yellow emission. The co-doping of Ce3+ significantly enhanced the luminescence of Dy3+ upon UV excitation (at a wavelength of 242nm) and the optimum co-dopant concentration of Ce3+ was found to be 3 mol%. Finally, the visible-NIR luminescence performance of Nd3+and Er3+ ions in silver zinc borate host glasses are discussed by means of visible and NIR luminescence spectral profiles. |
