Mechanisms of thermoluminescence (TL) in CaSO4:Dy are studied using electron spin resonance (ESR) in single-crystal samples. The ESR analysis indicates the presence of several variations of a distorted SO4- centre locally stabilised by a nearest neighbour Ca vacancy. This centre's structure, which has not been reported previously, relates to several centres observed in this system and could also explain results in related compounds. The presence of the Dy impurity, which increases the concentration of Ca vacancies due to charge neutrality requirements, enhances both the concentration of these centres and the intensity of the major TL peaks near 220 and 350 degrees C. The specific role of these and other previously reported centres in the TL of this material is followed using heat treatments. This enables one to identify centres that change in the range of the observed TL peaks as well as centres that seem to be related to one another by charge transfer or rearrangement. The behaviour of the observed centres and their relationship to the TL behaviour of the system reemphasises the complexity of this system.

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Optical absorption in irradiated and non-irradiated single crystals of CaSO4 and CaSO4:Dy is studied. The intrinsic defect centres SO4-, SO3-, SO2-, O3-, and O- are identified in irradiated samples. However, these centres are generally observed only if stabilised by Dy impurity ions within the structure. Dy2+ absorption is also observed in irradiated doped samples. Luminescence via energy transfer to Dy ions is corroborated by this study. Areas where these results may be used to develop further understanding of the thermoluminescence process in CaSO4:Dy are discussed.

Selective reactive ion etching of silicon nitride over silicon using CHF3 with N2 addition

General aspheric refractive micro-optics fabricated by optical lithography using a high energy beam sensitive glass gray-level mask Fabrication of planar quantum magnetic disk structure using electron beam lithography, reactive ion etching, and chemical mechanical polishing Variable shaped electron-beam lithography application to subwavelength and computer generated diffractive optics fabrication Masked ion beam lithography ͑MIBL͒ was employed to fabricate optical filters as a critical component of an energy conversion system which utilizes semiconductor photovoltaics. This article will describe the operation and novel application of these devices and the MIBL pilot production line being facilitized. The conversion concept, thermophotovoltaics ͑TPV͒, when coupled with these MIBL produced bandpass filters, is capable of converting heat to electrical power with Ͼ20% conversion efficiency. The EDTEK TPV filter is based on a high density array of slotted antenna elements patterned into a single layer of thin gold film.