TitleAlkali-phosphate common-ion system for synthesis of rare-earth orthophosphates
NameUhrin, Robert (author), Riman, Richard E. (chair), Greenhut, Victor A. (internal member), Wenzel, John T. (internal member), McCandlish, Larry E. (outside member), Rutgers University, Graduate School - New Brunswick,
SubjectMaterials Science and Engineering,
DescriptionRare-earth orthophosphate crystals are interesting materials for many optical applications, because their physical properties often exceed those of currently used materials. In particular, Ce:LuPO4 is useful for positron emission tomography (PET). The most important reason why this and other rare-earth orthophosphate crystals haven’t been commercialized is the absence of large crystals suitable for devices. The greatest impediment is the lack of a suitable crystal growth process. A Pb2P2O7 solution has been used for many years to produce a complete series of lanthanide orthophosphate crystals, but this solution raises some serious environmental concerns. In addition, large crystals of a reproducible size and quality that are required for device fabrication do not result, and the crystals tend to be platy. It is generally known that a change in solution acidity or basicity affects the habit of grown crystals. Consequently, it was theorized that a potassium-based system (i. e. more basic) would result in equiaxed crystals, and such a system has been investigated in an effort to obtain a partial phase diagram for the KPO3-Lu2O3 pseudo-binary system. Various techniques were employed to confirm a molten solution composition from which crystals can be grown. LuPO4 crystals were produced from solutions with different K2O/P2O5 ratios and varied Lu2O3 concentrations. This provided information on the preferred composition range for single phase LuPO4, as well as the solid phases expected within the range of compositions that was studied. X-ray diffraction (XRD) analysis provided a useful tool to identify the solid phases. Powder synthesis with subsequent XRD analysis was also utilized in some cases, since numerous single and mixed phosphate compounds are possible and a complete set of diffraction files is not available. Knowledge of the cerium concentration is also required in the case of Ce:LuPO4, so a K2O-CeO2-Lu2O3-P2O5 glass was developed. Samples containing varied cerium concentrations were examined using optical absorption spectrometry in order to correlate the ultraviolet peak height with cerium concentration. Finally, differential thermal analysis (DTA) was employed to identify the location of phase transitions within the selected composition range. These data were then utilized to construct a partial phase diagram up to 5 m% Lu2O3. The predicted composition/temperature range was applied to produce small, optically transparent, equiaxed crystals of Ce:LuPO4, Ce:GdPO4, Nd:LuPO4, YPO4, TbPO4, and CePO4. This confirmed that the KPO3-based solution was universally applicable to a complete range of lanthanide orthophosphates. Furthermore, it could be concluded that other alkaline solvents such as LiPO3 and NaPO3 might produce similar results.
NoteIncludes bibliographical references
Noteby Robert Uhrin
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.