Intrinsic defect related optical properties of pure and rare-earth-doped LiMgPO4

We report an experimental study on intrinsic defects in pure and rare -earths doped lithium -magnesium phosphate LiMgPO4. A wide range of optical methods were used in the work, including photoluminescence, thermoluminescence, radioluminescence and optical absorption. A detailed investigation made it possible to conclude that the main type of intrinsic defects responsible for all kinds of luminescence in LiMgPO4 is neutral oxygen vacancy (VO0), i.e., a vacancy with two trapped electrons. Lithium magnesium phosphate has been shown to be a thermoluminescent (TL) material. The TL response of LiMgPO4 is significantly enhanced by doping with praseodymium, cerium or europium. At the same time, the spectra of LiMgPO4: RE (RE - Ce, Pr, Yb) do not contain the lines associated with f -f transitions in RE3+ but are completely identical to the TL spectrum of the phosphate host. The energy transfer from RE to the host is suggested as an explanation for the observed effect.