Papers by Author: M. Zachau

Abstract: Nano-crystalline YAG:Ce (Y3Al5O12:Ce) with an average particle size of 10-50 nm was synthesized by the vapour phase reaction (CVR) in a hot-wall reactor. This nano-crystalline luminescent material has the advantage of a high light-conversion efficiency associated with superior light-scattering properties. Phases and compositions were analyzed by XRD and EDX, respectively. Photoluminescence was used to investigate the optical properties of the YAG host lattice doped with Cerium. As a first step the conditions for the in-situ production of the YAG phase were established. On the basis of previous DSC investigations of YAG phase formation, the DSC results were analyzed according to the Kissinger theory for thermally activated transformations. From the results it is predicted that, with sufficient heat transfer during the residence time of the particles in the hot zone of the reactor, YAG can be obtained in-situ during the CVR process. By modifying the parameters and the CVR setup it was possible to achieve conditions, which allow the production of in-situ YAG. Samples with Ce doping concentrations ranging from 0 to 2.65 at.% Ce were prepared to investigate the influence of the doping concentration on the luminescence of YAG:Ce.

Abstract: Luminescent and non-luminescent nano materials are used today in a variety of lighting applications. One example is the thin layer of densely packed nano alumina between glass and phosphor in fluorescent lamps that serves to increase the efficiency, to improve the maintenance and to reduce the mercury consumption of the lamps. Further, non-luminescent nano materials may be used to form a thin conformal coating around phosphor particles that protects the phosphor particles and improves the efficiency and maintenance of fluorescent lamps. Luminescent nano materials have been the subject of extensive research in the last 15 years. For particle sizes below 20 nm, the optical properties of nano phosphors change, e.g. the exciton energy increases and perhaps even more important, scattering decreases. We have synthesized nano Y2O3:Eu of particle sizes down to 10 nm, derived its optical properties, and investigated its use in Hg-free fluorescent lamps based on the Xe-excimer discharge. The possibility of using nano phosphors, e.g. semiconducting nano phosphors as CdSe or rare-earth doped phosphors as LaPO4:RE in LEDs, will be discussed.