Mark E. Hannah

An Investigation of Self-Absorption and Corresponding Spectral Shift in Phosphors

Many light emitting diode (LED) phosphors have overlapping emission and absorption bands, such as Ce 3+ -doped garnets and Eu 2+ -doped silicates, nitrides, and oxynitrides. These overlapping bands inevitably lead to self-absorption effects through either nonradiative energy transfer mediated via electron-electron correlation process or actual emission and radiative energy transfer which involves emission and absorption of a photon due to spectral overlap. The first process has been often discussed in the literature. The second process has been investigated in this work through a semi-quantitative formalism. Spectral shift, changes in emission peak shape, photoluminescent conversion efficiency, and phosphor characterization are discussed in light of self-absorption. The simulated results are compared to experimental data and shown to correlate well with observed data.

EPD of Phosphors for Display and Solid State Lighting Technologies

Electrophoretic deposition (EPD) has been used for phosphor screening for a variety of emissive information displays and more recently, for solid state lighting. EPD is well suited to deposit the fine (nanometer to micrometer diameter) phosphor particles needed for high resolution displays. The fundamentals of the EPD process in an isopropanol (IPA) bath have been characterized by the dissociation behavior of nitrate salts in IPA, measurement of the effects of pH and nitrate salt concentration on the zeta potential of the particles, studying of the processing conditions and modeling of the deposition rates. The electrochemical precipitation reactions form an adhesive agent for the particles and the adhesion strength can be enhanced by various methods to meet the requirements of these technologies.