Micro and Nanocrystalline LuPO_{4}(Ln^{3+}: Nd, Pr) Morphology, Luminescence and Inter-ionic Interplays

Abstract

The effect of dopants (Nd³⁺, Pr³⁺) introduced into micro and nanocrystals of LuPO₄ on their structural, morphological, and luminescent properties has been examined. The tetragonal structure of the synthesized phosphates was confirmed by means of an X-ray diffraction study. Transmission electron microscopy of LuPO₄ samples doped with 0–2% Pr³⁺ and 0–3% Nd³⁺ obtained by the microwave hydrothermal method showed the formation of the nanocrystalline samples with a size of 40–90 nm. Spectroscopic study of Lu_1-x-yPr_xNd_yPO₄ micro and nanocrystals showed that effective energy transfer occurs between the selected optically active ions. Due to significant ion–ion interactions in the co-doped orthophosphates, the contribution of nonradiative processes to the relaxation of the luminescent levels of praseodymium and neodymium effectively increases. The energy transfer in the micro and nanocrystals Lu_1-x-yPr_xNd_yPO₄ from Pr³⁺ ions to Nd³⁺ ions results in the efficient near-infrared emission in the region of the spectrum between 1064 and 1350 nm, whereas for Lu_1-x-yPr_xNd_yPO₄ nanocrystals doped with Pr³⁺ and Nd³⁺ ions, a particularly intense Nd³⁺ luminescence appears at 1064 nm. There is a significant impact of concentration of the Pr³⁺ and Nd³⁺ ions on near-infrared luminescence intensity of the studied Lu_1-x-yPr_xNd_yPO₄ phosphates. The relaxation dynamic of the neodymium metastable excited state is substantially sensitive to a variety of praseodymium admixtures, and inversely, the experimental lifetime of ¹D₂ Pr³⁺ emission level gradually decreases with increasing Nd³⁺ concentration.