Methods to enhance upconversion efficiency from lanthanide-doped nanomaterials

To improve the upconversion emission efficiency is still a main challenge of all the lanthanide-doped upconversion nanomaterials in order for them to have practical applications such as in data storage, multicolor display, bioimaging, and optoelectronic devices. In this presentation, we explained the possibilities to improve the upconversion emission efficiency of the nanomaterials by more than 10-fold. First, we verify by aberration corrected TEM technique to show that the recovery of surface defects can enhance visible emission efficiency of the upconversion nanomaterials under near-infrared excitation [1]. Furthermore, we show that by using core-shell-shell structure of the upconversion nanomaterials, we can improve the effective energy transfer between core and shells so that the influence of non-radiative recombination and transfer can be significantly suppressed [2]. As a result, deep ultraviolet emission can be obtained under near-infrared excitation. We also demonstrate that the use of optical feedback can control the population inversion at the upper levels of the lanthanide ions so that high emission efficiency can be sustained by laser action [3]. Finally, the use of phonon to assist population inversion in the Tm3+ doped nanomaterials is explained. It can be shown that upconversion emission efficiency at visible regime can be obtained from the upconversion Tm3+ doped nanomaterials under near-infrared excitation at high temperature (473 K) [4].