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Electron tunnelling phenomena in YPO4 : Ce,Ln (Ln = Er, Ho, Nd, Dy)

Electron tunnelling from an Ln2+-electron trap (Ln = Er, Nd, Ho, Dy) to a Ce4+-recombination centre is investigated experimentally and theoretically in YPO4 : Ce3+,Ln3+. Low temperature thermoluminescence, fading and isothermal decay measurements for samples with concentrations of Ce and Ln ranging from 0.05 to 5.0% are analysed. We observe a temperature activated tunnelling that depends on type of Ln and concentration. Results are simulated with simple quantum mechanical concepts. The average distance between traps and centres is altered by the Ce and Ln concentrations. The higher the concentration, the higher the electron tunnelling probability which can be attributed to a shorter average Ce4+–Ln2+ distance. As a result, changes in the thermoluminescence characteristics like the fading rates and the isothermal decay curves are observed.