Upconverting Nanoparticles

TLDR

Upconversion is a nonlinear optical process where sequential absorption of multiple photons produces anti‑Stokes emission, efficiently excitable even at low densities, and is most effective in rare‑earth doped solid‑state materials, making UC nanoparticles promising alternatives to organic fluorophores and quantum dots for medical imaging. The study aims to develop synthesis routes for highly efficient, small UC nanoparticles with narrow size distribution that can form transparent solutions across many solvents. The authors propose synthesis methods that yield highly efficient, small UC particles with narrow size distribution capable of forming transparent solutions in diverse solvents. High‑quality UC nanocrystals can be routinely synthesized with controllable solubility, size, crystallographic phase, optical properties, and shape.

Abstract

Abstract Upconversion (UC) refers to nonlinear optical processes in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength (anti‐Stokes type emission). In contrast to other emission processes based on multiphoton absorption, upconversion can be efficiently excited even at low excitation densities. The most efficient UC mechanisms are present in solid‐state materials doped with rare‐earth ions. The development of nanocrystal research has evoked increasing interest in the development of synthesis routes which allow the synthesis of highly efficient, small UC particles with narrow size distribution able to form transparent solutions in a wide range of solvents. Meanwhile, high‐quality UC nanocrystals can be routinely synthesized and their solubility, particle size, crystallographic phase, optical properties and shape can be controlled. In recent years, these particles have been discussed as promising alternatives to organic fluorophosphors and quantum dots in the field of medical imaging.