Upconversion luminescence of nanophosphors Mechanisms and properties

Due to the unique characteristics of converting near-infrared (NIR) excitation to tunable emission from deep ultraviolet to NIR, lanthanide ions–doped upconversion (UC) nanomaterials are considered to have great potential in a broad range of applications, including biomedicine, display, energy, anti-counterfeiting and super-resolution imaging. Although UC materials have attracted numerous attentions in the past over 50 years, insufficient UC efficiency and incomplete understanding of microscopic physical picture of UC still hinder the practical application of such materials. In this chapter, we review the basic UC mechanisms and introduce the main strategies to enhance UC luminescence, focusing on the latest developments in nanoscale materials, such as core-shell structure design and concentration quenching inhibition. Finally, some new understandings of UC dynamics based on Monte Carlo simulation are introduced.