Münster University of Applied Sciences

About: Münster University of Applied Sciences is a education organization based out in Münster, Germany. It is known for research contribution in the topics: Luminescence & Laser. The organization has 694 authors who have published 1067 publications receiving 12597 citations.

On the Photoluminescence Linearity of Eu2+ Based LED Phosphors upon High Excitation Density

Abstract: h t t p : / / w w w . f h m u e n s t e r . d e / j u e s t e l Background The current standard architecture for SSL is the phosphor-converted light-emitting diode (pc-LED) in which high brightness LEDs based on (In,Ga)N are combined with one or more down-converting phosphors to produce composite white light of nearly any color temperature and color rendering quality. Nonetheless their tremendous success in pc-LED design, blue LEDs have one well-known and central drawback: a non-thermal drop in efficacy with increasing power density. This “efficacy droop” restricts operation to reasonably low input power densities, disagreeing to the wish to extract more photons per unit area of the LED chip and thereby make SSL more affordable. A solution to overcome the efficacy droop of blue LEDs, could be the use of LDs. Operated in stimulated emission, in principle high efficacies at much higher input densities than for LEDs can be reached. Certainly, at high input power densities state-of-the-art, high power blue, edge emitting LDs have already reasonably high (30-40%) powerconversion efficiencies, and a steady increase within the next years in efficiency can be expected. A requirement of LDs for SSL is the ability to create white light. In principle, the same phosphors used in the pc-LED architecture can also be used with LDs. Indeed there are various reports dealing with phosphor-converted LDs (pc-LDs). Especially, Eu2+ activated phosphors are commonly used. These phosphors, excited by high radiance pump sources, like high power LDs, offer considerable potential for high radiance conversion in SSL. Remarkably, theoretical arguments suggest that the radiance of the luminescent spot should increase linearly with the excitation density of the incoming light source up to 1 kW/mm2. In practice, however, thermal quenching and (non-thermal) optical saturation limit the maximum attainable radiance of the luminescent material. In this work we present experimental data of the widely applied LED phosphors (Sr,Ba)2SiO4:Eu 2+ (OSE), (Sr,Ca)2Si5N8:Eu 2+ (258:Eu), and CaAlSiN3:Eu 2+ (CASN:Eu), in which these limits have been investigated. These systems are particularly good for high radiance conversion by virtue of their short luminescence lifetimes and little thermal quenching.

Highly efficient energy transfer from Ge-related defects to Tb3+ ions in sol–gel-derived glasses

Abstract: Luminescence and excitation spectra of sol–gel derived silica co-doped with Ge and Tb and treated in reducing atmosphere are reported. Energy transfer from Ge-related defects to Tb centers is demonstrated with an efficiency close to unity, resulting in all-inorganic sol–gel-derived materials with up to 30% quantum efficiency upon excitation under 254 nm radiation.