Ulrich Peuchert

Reference based optical characterization of glass-ceramic converter for high power white LEDs

Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools and detection methods for product and process control, material sciences, environmental and bio-technical analysis, molecular genetics, cell biology, medical diagnostics and drug screening. According to DIN/ISO 17025 certified standards are used for fluorescence diagnostics having the drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is necessary to calculate absolute numbers like absorption/excitation cross section and quantum yield. This can be done for different types of dopants in different materials like glass, glass ceramics, crystals or nano crystalline material embedded in polymer matrices. Here we consider a special type of glass ceramic with Ce doped YAG as the main crystalline phase. This material has been developed for the generation of white light realized by a blue 460 nm semiconductor transition using a yellow phosphor or converter material respectively. Our glass ceramic is a pure solid state solution for a yellow phosphor. For the production of such a kind of material a well controlled thermal treatment is employed to transfer the original glass into a glass ceramic with a specific crystalline phase. In our material Ce doped YAG crystallites of a size of several µm are embedded in a matrix of a residual glass. We present chemical, structural and spectroscopic properties of our material. Based on this we will discuss design options for white LEDs with respect to heat management, scattering regime, reflection losses, chemical durability and stability against blue and UV radiation, which evolve from our recently developed material. In this paper we present first results on our approaches to evaluate quantum yield and light output. Used diagnostics are fluorescence (steady state, decay time) and absorption (remission, absorption) spectroscopy working in different temperature regimes (10 - 350 K) of the measured samples in order to get a microscopic view of the relevant physical processes and to prove the correctness of the obtained data.

New heavy metal oxide silicate amplifier glass for compact and broadband amplifiers

Properties of a new rare-earth doped heavy metal oxide containing silicate glass are presented. The glass has potential for fabrication of ultra-short wideband fiber and planar waveguide amplifiers. We report specific results for a fiber amplifier geometry, discussing achieved improvements in device compactness (Giles gain g* = 210 dB/m allowing up to 100 times shorter fiber) and amplification bandwidth (50% more bandwidth in C-/L-band) compared to the conventional EDFA. We also access the potential of this material for fabrication of active planar integrated waveguide devices.

Yb:YAG composite ceramic laser

Yb:YAG ceramic laser materials, fabricated by vacuum sintering technology, were optically investigated within different laser set-up configurations. The established nanopowder vacuum sintering process shows good potential for mass fabrication of multicomposite ceramic laser materials with different dopant concentrations. 5%, 7%, 10% single dopant and 7%/20% core-cladding multi-composite Yb:YAG materials were fabricated and investigated. The highest measured slope efficiency, for the composite ceramic laser materials was 81%, at 1030 nm emission wavelength, similar to Yb:YAG single crystals.