R-activated phosphors

G. Blase, Chemistry and physics of R-activated phosphors MJ. Weber, Rare earth lasers 275... 

Section 2 will give an introductory presentation of the essence of TL and of dosimetry. For deeper understanding the reader will be referred to monographs on these topics. The rest of the article will review the progress in the field and future trends. For the benefit of investigators who work in the field of R-activated phosphors the review will be ordered according to the host compounds. 

R change valencies easily for example, Eu ions show the transitions Eu " +->Eu. This corresponds in fact to the trapping of electrons or holes by the R activators in phosphors, which occurs in the processes of excitation and emission of TL in R-activated phosphors. 

This is the bulk section of the present article. It will present the main results of published papers and follow the progress achieved in the understanding and characterization of R-phosphors. The first commercial R-activated phosphors were reported in the l%0s. The merits of R as activators were recognized and by now a variety of high-sensitivity R-containing phosphors suitable for various dosimetric needs are available commercially. Investigations continue with the attempt of further improvement of the characteristics of existing TLDs and the introduction of new R-phosphors. 

Barium compound hosts. More has been published on R-activated Ba compounds compared to Sr compoimds. The two host compounds do not vary much in their properties as R-activated phosphors. In fact many papers deal with both Ba and Sr phosphors. The high effective Z of the Ba compoimds turns these phosphors further away fixim tissue equivalence compared to the Sr compounds. There are some variations in the energy dependence and in the TL intensities of the two phosphors. The R ions substitute for the alkaline earths in the lattice. The considerable difference between the ionic radius of Ba (0.153 nm) and that of Sr (0.112 nm) may explain the changes in the GCs of the two compounds. As before, the review will deal separately with the various host compounds. 

Blasse, G., 1979, Chemistry and physics of R-activated phosphors, in Handbook on the Physics and Chemistry of Rate Earths, Vol. 4, eds K, A Gschneidner Jr and L. Eyring (Nortli-Holland, Amsterdam) pp. 237 274. 

After introducing the reader to the principles that underlie thermoluminescence and its application to dosimetry, A. Halperin provides detailed information on the R-activated phosphors that support dosimetry. This is a selective review of a copious literature based on that fraction deemed to have most advanced the field. 

In section 2 of this chapter we shall examine the possible excitation and emission transitions in phosphors. Further we will deal with radiationless losses and energy transfer. This section is called Physics of Phosphors. In section 3 (Chemistry of Phosphors) we will consider the influence of chemical composition and crystal structure on the physical properties mentioned in section 2. In section 4 we will illustrate how the ideas presented in sections 2 and 3 work in the case of luminescent rare earth (R) ions where those ions that find technical applications nowadays will be treated in more detail. In section 5, finally, we shall take a look at the application of R-activated phosphors. 

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