Upconversion effective enhancement of NaYF:Yb/Er nanoparticles by Ni doping.

In this manuscript, Ni ions-doped NaYF:Yb/Er nanoparticles have been synthesized via a modified hydrothermal method. The upconversion luminescence intensities of the green (G) and red (R) emission of NaYF:Yb/Er co-doped with 20 mol% Ni ions are the strongest which increase 32.84 and 20.99 times than that without doping Ni, respectively. In addition, the R/G ratio decreases with the concentration of Ni increasing from 0 to 40 mol%. The underlying reason for luminescence enhanced and the R/G ratio decreased by Ni doping is explored by a series of controlled experiments, and the mechanism based on the crystal field asymmetry, different substitution by Ni, the energy transition of Er is studied in detail. The study indicates that the misshapen crystal field plays an important role in enhancement fluorescence emission, and several factors affect the R/G ratio including the crystal field, the substitution site and the energy transition. Our result may play a certain function for study and design of high-performance upconversion materials. [ABSTRACT FROM AUTHOR]