Photon upconversion from visible light to ultraviolet light

Abstract

In this review, several aspects of visible-to-ultraviolet (UV) photon upconversion (UC) based on triplet–triplet annihilation (TTA) are introduced and discussed. Because UV-UCs use higher energy triplet states, they are generally more prone to suffer from photodegradation compared to visible-to-visible UCs. First, the background, utility, and research situation of UV-UCs are explained and then some example of low photostability in previously reported UV-UC sample system is presented contrasted with the stability of visible-to-visible UC carried out in ionic liquid. Our recent findings regarding UV-UCs for the wavelength shorter than 340 nm are presented and discussed. Based on them, some general guideline for improving sample photostability is proposed.