报告题目：Investigation of Eu doped silicate apatite phosphors for LED applications
Development of novel phosphors for white light generation using light emitting diodes (LEDs) is an active research area due to such advantages1over other light sources as high efficiency, low power consumption, long service life, compact size etc. Silicates with apatite structure have a high potential for LED phosphor applications because of their stability and high efficiency.2,3,4We investigated luminescence properties of silicate apatitesM2Ln8(SiO4)6O2(whereM= Mg, Ca, Sr;Ln= Y, La), pure and doped with Eu3+ions (0.5-2.0 at. %). Ceramics were prepared by high-temperature solid-state reaction using precursors synthesized under hydrothermal conditions. Some samples were annealed in H2/Ar reducing atmosphere in order to convert Eu3+into Eu2+and to evaluate compounds with coexisting 4f-4f and 5d-4f transitions.
The complex structure of silicate apatites offers good opportunities for material engineering. There are two crystallographic sites in theIXA14VIIA26(SiO4)6O2structure5, which can be occupied by the alkaline earth (M2+) and rare earth (Ln3+) cations, they are 9 and 7-fold coordinated for A1 and A2 sites, respectively. Small radius Mg2+ions and larger Sr2+occupy preferentially the A2 and A1 sites, respectively, which results in some differences in luminescence properties of Eu-doped Mg-based and Sr-based apatites. Medium size Ca2+ions seem to populate mainly A1 sites and properties of Eu luminescence in Sr- and Ca-based apatites are similar. The excitation mechanisms in the energy range from visible-to-VUV and the properties of observed emissions (4f and 5d luminescence of rare earths, intrinsic and defect emissions of hosts) including decay kinetics were analyzed taking into account the peculiarities of apatite structure. The potential of Eu-doped silicate apatite phosphors for LED applications will be discussed.