Chapter 2 - What are upconversion nanophosphors: Basic concepts and mechanisms

Abstract

Lanthanide (Ln3+) doped upconversion (UC) nanophosphors have attracted immense attention in the last few decades due to their capability to convert near-infrared (NIR) radiation into shorter-wavelength ultra-violet (UV)-visible emissions. Their superior photophysical properties, namely large anti-stokes shifts, sharp emission bands, long luminescence lifetimes, low autofluorescence background, deep penetration depth, and high resistance to photobleaching make them excellent candidates for various physical and biological applications. In this chapter, we present an overview of the upconversion processes. After a brief introduction into the upconversion field, the fundamental photophysics of upconversion emission phenomena, including the different UC mechanisms, and excited state dynamics of Ln3+ ions involved in the UC processes are explained. Moreover, we discuss the major approaches to manipulate emission spectral properties and brightness, which play an important role in determining upconversion luminescence efficiency. Finally, we emphasize their major possible applications in the various fields including, lighting and displays, physical sensing, anticounterfeiting, biological sensing and detection, temperature sensing, etc.