In the present article we briefly review some materials research aspects related to ceramic phosphors and discuss both typical characteristics as well as unique features of such optical converters. Devices with more efficiency and/or higher luminous flux that are based on converting the pump light crucially enable the use of LEDs in white and single color illumination schemes for many applications. Advantages of generating white light with ceramics versus powder-in-silicone are discussed. High performance of single color conversion LEDs in terms of efficacy and external quantum efficiency for the visible region boost the output in data or home cinema projection and automotive signaling but more applications are appearing.

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An extension of a theorem for light extraction [Adv. Opt. Technol.2, 291 (2013)] from a higher index luminescent body (LED or phosphor) through an extracting surface into a lower index output medium is derived. The result is valid for both geometric and diffractive surface structures. Using this bound and radiation transport calculations, we show that extraction from LEDs or phosphors requires a combination of cavity effects to enhance radiance behind the extracting surface and scattering or diffraction to couple trapped total-internal-reflection modes to propagating modes. The treatment applies to macroscopic luminescent sources whose thickness exceeds the longitudinal coherence length of the luminescent radiation.

The surface chemistry differences between two alumina powders is shown to have a significant effect on the properties of concentrated aqueous dispersions of the powders. The initial dispersion pH and magnitude and sign of the initial mobility of the particles (determined by acoustophoresis) are different for the two powders because of differences in surface impurity contents. As a result, the two powders require different amounts of dispersant to achieve stability in dispersions near their isoelectric points. The surface chemistry differences between these two aluminas illustrate the importance of examining ceramic dispersion properties at the concentrations used in processing the material. [