Effect of the chemical impurities on the luminescence emission of natural apatites

• We report the cathodoluminescence and blue thermoluminescence of natural apatites.
• We characterized the samples by X-ray diffraction and Raman spectroscopy.
• The apatites show CL wavebands linked to Ce3+, Tb3+, Dy3+, Sm3+, Pr3+, Mn2+ and UO22+.
• All the studied aliquots exhibit one single UV–blue TL peak at 370, 256 and 268 °C.
• The crystallinity index are related with the different compositions of the apatites.

This paper reports on both cathodoluminescence (CL) and blue thermoluminescence (TL) emission of well-characterized natural Spanish and Brazilian apatites [Ca5(PO4)3(OH, F, Cl)]. Chemical analyses performed by means of Electron Microprobe Analysis (EMPA) have shown the presence of trace elements that can induce CL bands. In this sense, the apatites shown emission bands peaked at 3.26, 2.86, 2.62, 2.14, 2.02 and 1.94 eV are respectively linked to substitutional Ce3+, Tb3+, Dy3+, Pr3+, Sm3+ and Mn2+ in structural Ca2+ positions. The 3.18 eV emission band can be associated with intrinsic electron defects on oxygen of the phosphate group (PO4)3−. The presence of (UO2)2+ gives rise to an emission at 2.14 eV. All the studied aliquots exhibit one single UV–blue TL peak that modifies the position from one sample to another (370, 256 and 268 °C) probably due to (i) the variation in the crystallinity index (from 0.88 to 1.34) and (ii) successive chemical processes such as oxidation, dehydration, dehydroxylation, and fluorine ions losses due to the thermal readout.

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