A Hole Center Causing Rose Coloration in AlPO 4 and GaPO 4

In synthetic AlPO 4 crystals and Sn‐doped GaPO 4 hole centers localized on an oxygen showing an almost isotropic hyperfine splitting from a 31 P nucleus are observed after X‐ray irradiation and analyzed by EPR. They are evidently caused by substitution of Al and Ga, respectively, by a divalent cation, most likely Mg 2+ . From the variation of the EPR linewidths with temperature an activation energy of 19 kJ/mole for thermal hopping of the hole is found in AlPO 4 . These centers cause a rose coloration and the first absorption band in AlPO 4 has an oscillator strength near 0.3, in the same range as for the smoky quartz centers. It is interpreted as arising from optical transfer of the hole within the PO 4 unit. Thermoluminescence emission is observed with destruction of the centers in AlPO 4 . From glow curves an activation energy of 136 kJ/mole is obtained which in this case represents the distance of the hole from the valence band. The properties of the center in AlPO 4 are compared to those of a similar center in certain natural rose‐colored quartz crystals.