Development of ZnTe Powder Phosphor for Protein Crystallographic X-ray Detectors
DESCRIPTION (provided by applicant): We propose to develop a new phosphor for X-ray detectors used in protein crystallography, which can be used both in the home laboratory and at synchrotron beamlines. The phosphor, ZnTe:O, will be at least 3 times brighter than the conventional Gd2O2S:Tb currently used almost universally on such detector systems. ZnTe:O will also have a faster time response than Gd2O2S:Tb. ZnTe is chemically similar to ZnSe, with which PhosphorTech has already successfully developed an excellent phosphor, ZnSe:Cu,CI. ZnSe:Cu,CI is now a commercial product distributed by PhosphorTech. ZnSe:Cu,CI has been used for the past 6 years by Bruker AXS Inc. of Madison, Wl for its chemical crystallography CCD detectors. Bruker sells almost 90% of all chemical crystallography instruments in the USA and Europe, and our ZnSe phosphor has been an important reason for the success of their product, since it is well liked by Bruker customers. However, since it contains selenium, this phosphor is inappropriate for protein crystallography, in which selenium is the preferred element for anomalous dispersion phasing. The presence of an absorption anomaly at exactly the X-ray energy (12,658eV) used for phasing, would ruin these measurements. ZnTe will solve this problem, since the tellurium absorption anomalies are at different X-ray energies (4,341eV and 31,814eV). Theoretically ZnTe phosphors should be as bright, or brighter, than ZnSe phosphors. However, since tellurium is more chemically reactive than selenium, it is more difficult to work with. Thus our preliminary efforts to make a ZnTe:O phosphor have resulted in material that is initially very bright, but slowly oxidizes in the presence of water vapor, shortly after synthesis. During Phase I of this project, we will find methods to increase the inherent brightness of ZnTe:0, and to passivate and protect newly synthesized ZnTe:O powder, to prevent chemical deterioration of the material. We anticipate that in Phase II we will develop the means to produce commercial quantities of this stabilized powder, and fabricate large, high quality phosphor screens that can be used in commercial CCD detectors for protein crystallography.
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