Recent progress of energy transfer and luminescence intensity boosting mechanism in Nd3+-sensitized upconversion nanoparticles

Rare earth doped upconversion nanoparticles can be considered as the spice of research in the field of luminescence nanomaterials due to their unique optical properties such as near-infrared excitation. Enormous works have been reported about biomedical applications of 980 nm excited and Yb3+-sensitized upconversion nanoparticles. However, 980 nm excitation wavelength overlaps with the absorption band of water molecules in the biological environment, leading to overheating effect that can induce thermal damages of normal cells and tissues. Recently, Nd3+-sensitized upconversion nanoparticles which can be excited with 808 nm has been widely investigated as alternative nanoparticles that can surmount this issue of overheating effect. Even though Nd3+-sensitized upconversion nanoparticles can reduce the overheating effect by 20 fold as compared to Yb3+-sensitized counterpart, there are several factors that reduce the upconversion luminescence intensity. In this review article, photon energy harvesting and transferring mechanisms in Nd3+, Yb(3+ )and emitter ions co-doped upconversion nanoparticles under 808 nm excitation are briefly discussed. Factors that affect upconversion luminescence intensity and quantum yield of Nd3+-sensitized upconversion nanoparticles are also addressed. Besides, some of the important strategies that have been recently utilized to boost upconversion luminescence intensity of Nd3+ sensitized upconversion nanoparticles are thoroughly summarized. Lastly, the future challenges in the area and our perspectives are in sight. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.