Pure and intense orange upconversion luminescence of Eu3+ from the sensitization of Yb3+–Mn2+ dimer in NaY(Lu)F4 nanocrystals

Abstract

The pure and intense orange upconversion luminescence of Eu³⁺ was efficiently achieved in NaYF₄ and NaLuF₄ nanocrystals through the upconversion sensitization of doped Yb³⁺ and Mn²⁺ ions dimer for the first time. A shell-coating strategy was performed to further enhance the emission intensity. In this work, a novel upconversion mechanism for energy transfer from the Yb³⁺–Mn²⁺ dimer to the Eu³⁺ ion was proposed by analyzing the upconversion luminescence spectra, lifetimes and pumping photons measurements of the obtained nanocrystals in detail. The applications of the nanocrystals for CT imaging and ratiometric pH sensing in physiological pH range were performed. This study also provides a new upconversion spectral region at around 592 nm for applications in multicolor imaging, multiplexed encoding and detection.