Luminescent properties of crystalline YAG:Ce for white LED applications
Performed is a comparative study of the characteristics of YAG:Ce luminescent converters with single-crystalline, cellular and polycrystalline structure obtained by the method of directed crystallization of the melt. Peculiarities of the structure and surface morphology of the converters are found to essentially influence their spectral characteristics and luminescence efficiency. It is shown that polycrystalline converters based on YAG:Ce are promising for application in white light emitting diodes.
Solid State Light Source Fabricated with YAG:Ce Single Crystal
A solid state, yellow-white emitting light source has been manufactured employing a YAG:Ce single crystal as a wavelength conversion material to analyze the conversion process quantitatively and also to explore the ultimate limit of the conversion efficiency. Excitation polarized coherent blue light is incident on to the crystal at the Brewster angle and is multiply reflected inside the crystal with internal total reflection. The generated light is shown to be efficiently extracted by providing a light guide with a suitable shape at the front surface of the crystal.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.