Inorganic phosphor coatings for UV-responsive CCD image sensors

Abstract

Conventional CCD image sensors have low responsivity in the ultraviolet region of the spectrum because the small absorption depth results in electron generation in the gate of the CCD rather than in the buried channel. Inorganic phosphor coatings to convert UV to visible light have been developed through the collaborative efforts of the University of Waterloo and DALSA Inc. In general, the coatings are simple to deposit and have been used to obtain images at illumination wavelengths of 265 and 365 nm. The developed coating is similar to acrylics doped with organic laser dyes presented in previous papers; here, the organic dye has been replaced with an inorganic phosphor material. Organic laser dyes have the advantage of nanosecond to microsecond decay times and the availability of a variety of dyes enables the customization of the absorption and emission wavelengths, however, they quickly degrade upon exposure to UV radiation. In many manufacturing applications, higher UV illumination intensities will degrade the laser dyes in a relatively short time. Inorganic phosphors exhibit reduced degradation rates thereby improving the viability of phosphor coated CCD image sensors for commercial and manufacturing applications. The quantum efficiency improvement of the coated sensor over the uncoated sensor is 350% and 86% at 265 and 365 nm, respectively.