Wolfgang Rossner

Single Chip White LEDs

The operation principles of the various single chip luminescence conversion (LUCO).white LEDs, that can be realized with blue or ultraviolet (UV) LED chips, are briefly reviewed. In order to demonstrate the feasibility of the so far almost unexplored case of UV pumped tricolor LUCO white LEDs, In x Ga 1-x N single quantum well LED layer sequences were grown by MOCVD and processed into near-UV LED pump chips. Europium doped oxide and sulfide phosphors emitting in the blue, the green and the red spectral range were used for UV to visible conversion. With white blends prepared from these phosphors, housed white LEDs with high color quality were realized.

Ultraviolet Pumped Tricolor Phosphor Blend White Emitting LEDs

Near-UV and violet emitting AlGaInN single quantum well LED structures were grown by MOCVD on sapphire substrates. On-wafer tests before processing gave an output power at 40 mA between 1.4 mW at 380 nm and 6.7 mW at 420 nm. LED chips with wavelengths between 380 and 404 nm were selected for manufacturing radial UV LEDs and white emitting LEDs. The UV to white converters were prepared from broad band red, green and blue emitting powder phosphors with individual luminescence peaks near 610, 550 and 460 nm, respectively. White luminescence conversion (LUCO) LEDs with a warm hue and color temperatures in the range 4000-4300 K are demonstrated.

The conversion of high energy radiation to visible light by luminescent ceramics

The properties of luminescence ceramics which are roughly based on rare-earth doped oxides, oxysulfides, garnets, and silicates have been investigated. The characteristic luminescence data of the ceramics considered, such as emission spectra and decay, are similar to those of corresponding powders or single crystals. However, conversion efficiency, afterflow, and energy resolution are strongly affected by ceramic processing due to its influence on the microstructure, final optical quality, and defect structure. In this connection residual pores and grain boundaries play an important role. For example, the insufficient optical quality of Gd/sub 2/O/sub 2/Sr:Pr,Ce-ceramics is the main reason not only for a reduced light output but also for a rather pronounced degradation of the energy resolution, beyond the merely statistical limit. Consequently, luminescent ceramics, at least in their present form, appear not be suited for spectrometric applications. In the case of scintillation counting, the presented ceramics exhibit rather high decay constants giving low count rates. This drawback can be improved by using activator dopants with faster optical transition. >

The influence of aliovalent impurities on the luminescence of (Y,Gd)2O3a: Eu

Abstract The effect of Mg2+ and Ti4+ additions on X-ray excited luminescence of (Y,Gd)2O3:Eu3+ ceramic specimens is investigated. While Mg2+ has minor influence, Ti4+ additions reduce luminescence light yield and afterglow, assuming that non-radiative transitions and competitive optical absorption by Ti3+ formation are involved.

AlGaIn)N ultraviolet LED chips and their use in triphosphor luminescence conversion white LEDs

We report on the development of (AlGaIn)N quantum well LEDs covering the 380 to 430 nm wavelength range, which serve as the primary light source for tri-phosphor luminescence conversion white LEDs. Epitaxial layer growth was performed by low-pressure metal-organic chemical vapor deposition on sapphire substrates. Mesa LEDs were fabricated and either mounted in standard epoxy-based 5 mm radial LED packages or flip-chip bonded on ceramic submounts. Then, LED-chips with peak wavelengths matching the absorption spectrum of an appropriately chosen inorganic tri-phosphor blend, were used for the fabrication of single-chip tri-color luminescence conversion white LEDs. These de-vices allowed us to demonstrate the feasibility of the above concept for improved color rendering and tunability.

Pressureless Sintering of Luminescent CaAlSiN3:Eu Ceramics

CaAlSiN 3 :Eu powder compacts were pressureless-sintered in a nitrogen atmosphere between 1400 and 1800 °C. The sintering behavior and the dependence of the luminescence properties on the sintering temperature were investigated. It is shown for the first time that it is possible to sinter CaAlSiN 3 :Eu ceramics that efficiently emit light starting from a micrometer-sized phosphor powder optimized for high luminescence efficiency. The maximum densities of the ceramics were achieved at ≥ 1700 °C and are limited to 80 % of the solid-state density owing to inhomogeneities of the powder compacts caused by the applied binder-free dry-pressing procedure. The phase composition of the ceramic specimens as well as the luminescence properties remained unchanged during sintering. These results demonstrate that pressureless sintering is suitable for fabricating CaAlSiN 3 :Eu bulk ceramics that can be used for LED applications.