Ultra‐Violet Excited Paramagnetic Centres in Calcium Tungstate

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Abstract
Two sets of paramagnetic species having a spectroscopic splitting factor slightly higher than the free electron value are produced in CaWO4 doped with copper after irradiating the crystal with ultra‐violet light. One set of lines is identified as being due to a hole trapped at a single tungsten site and is found to bleach out on warming the crystal through the thermoluminescence glow peak at 160 °K. The other set of lines increases in intensity first with the emission of light in the 160 °K peak and then again with the 260 °K peak and bleaches out on heating the crystal through the thermoluminescence glow peak at 400°K. The copper does not take part in the excitation process directly. It is suggested that the low temperature paramagnetic species arises from the loss of an electron from the tungstate complex.