High resolution luminescence spectroscopy and thermoluminescence of different size LaPO4:Eu3+ nanoparticles

Nanoparticles (5 nm) and nanorods (2 nm x 15 nm and 4 nm x 20 nm) of monoclinic monazite LaPO4:Eu3+ were prepared by reverse micelle and co-precipitation techniques. Effects of the particle size and surface defects on the intensity of luminescence and the emission spectrum shapes were analyzed by high resolution spectroscopy under laser (266 nm) and X-rays excitation. All synthesized LaPO4:Eu3+ samples showed similar spectral features with characteristic Eu3+ ions emission bands: D-5(0)-> F-7(0) centered at 578.4 nm, magnetic-dipole transition D-5(0)-> F-7(1) at 588-595 nm, electric-dipole transition D-5(0)-> F-7(2) at 611.5-620.5 nm, D-5(0)-> F-7(3) at (648-652 nm) and D-5(0)-> F-7(4) at (684-702.5 nm), with the most dominant electric-dipole D-5(0)-> F-7(2) transition. Additionally, the thermally stimulated luminescence was studied for the most dominant peak at 611.5 nm. It was shown that the Eu3+ doping creates traps in all samples. Two prominent and well resolved glow peaks at 58.7 K and 172.3 K were detected for 5 nm nanoparticles, while low-intensity glow-peaks at 212.1 K and 212.2 K were observed in the X-rays irradiated nanorods. Displayed glows could be attributed to free and bound electrons and holes or to the recombination of electrons of ionized oxygen vacancies with photogenerated holes. To obtain information about the processes and specific defect type it is necessary to carry out additional analysis for all synthesized samples. The glow curves were analyzed and trap parameters were estimated and discussed throughout the paper.