EPR evidence of surface paramagnetic defects formation due to annealing of LaF3 nanoparticles

An EPR technique and optical measurements have been applied to study LaF3 nanoparticles doped with 7% of Pr3+ ions. It has been found that vacuum annealing of the studied samples leads to the appearance of paramagnetic defects with g-factor close to the value which is typical for the electron trapped in a fluorine vacancy. The concentration of paramagnetic defects was reduced after fluorination of initial nanoparticles. The possible origin of surface defects due to vacuum annealing is discussed. The results of the study can help to improve the performance of fluoride nanoparticles for biomedical applications.