Pixelated phosphors for high-resolution and high-contrast white light sources: erratum.

Erroneous absolute luminance values of the pixelated phosphor structure B25 (pixel size of 25 microns by 25 microns) have been corrected. The updated figure shows clearly the potential of the investigated structure as light-converter for high-resolution lighting systems.

Pixelated phosphors for high-resolution and high-contrast white light sources.

Porous phosphor microstructures are studied for their potential as light converter in laser-based, high-resolution lighting systems. Phosphor particles are filled into pre-patterned silicon molds and coated by an atomic layer deposition with a thin layer of Al2O3 for mechanical stability. Pixel sizes of 2 mm by 2 mm down to 25 µm by 25 µm are fabricated. The structures show a significant drop in luminance between the illuminated and the non-illuminated, adjacent pixel. The high thermal conductivity of the silicon allows an efficient cooling of the structures. Having removed the backside silicon, an active air flow cooling of the porous phosphor structure is possible.

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy.

The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu 2 + and Eu 3 + ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between - 12 and - 15 mm/s for Eu 2 + compared to around 0 mm/s for Eu 3 + . Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu⁻X bond length.