Robert Joseph Lyons

Development of the HiLightTM scintillator for computed tomography medical imaging

Abstract The image quality of computed tomography (CT) medical scanners is extremely sensitive to afterglow, radiation damage and optical non-uniformities of scintillators used in X-ray detectors. This represents a tough challenge in the design of scintillator materials with optimum properties. Discussion will center on the development and properties of the first commercialized transparent ceramic scintillator, the (Y,Gd)2O3:Eu-based HiLightTM scintillator used in GE Medical Systems CT products. The flexibility of the ceramic scintillator platform has enabled it to be engineered to satisfy the changing needs of CT imaging, which is demonstrated by its successful incorporation into over 8000 CT systems worldwide since 1988. The ceramic process makes possible uniform co-doping at ppm levels to control electronic defects responsible for afterglow, reducing it to levels below detectibility in CT images. Annealing of the material in controlled oxygen atmospheres, combined with rapid oxygen diffusion along grain boundaries in the ceramic, reduces radiation damage to negligible values. Transient thermoluminescence of these materials will be discussed as a diagnostic of electronic trap levels responsible for both afterglow and radiation damage. Finally, with the increased scan speed requirements of modern CT systems, energy transfer between the Eu activator and other rare-earth ions can be used to speed the radiative decay of the scintillator, ensuring the materials continued viability in future CT systems.

Optimized Phosphors for Warm White LED Light Engines

The objective of this program is to develop phosphor systems and LED light engines that have steady-state LED efficacies (using LEDs with a 60% wall-plug efficiency) of 105–120 lm/W with correlated color temperatures (CCT) ~3000 K, color rendering indices (CRI) >85, <0.003 distance from the blackbody curve (dbb), and <2% loss in phosphor efficiency under high temperature, high humidity conditions. In order to reach these goals, this involves the composition and processing optimization of phosphors previously developed by GE in combination with light engine package modification.

Phosphor Systems for Illumination Quality Solid State Lighting Products

The objective of this program is to develop phosphor systems that will enable LED lamps with 96 lm/W efficacy at correlated color temperatures, (CCTs) ~3000 K, and color rendering indices (CRIs) >80 and 71 lm/W efficacy at CCT<3100 K and CRI~95 using phosphor downconversion of LEDs. This primarily involves the invention and development of new phosphor materials that have improved efficiency and better match the eye sensitivity curves.