Emission spectra tuning of upconverting NaGdF4:20% Yb, 2% Er nanoparticles by Cr3+ co-doping for optical temperature sensing

Abstract Upconverting (UC) nanoparticles have gained much attention due to their unique properties of converting radiation with longer wavelength (usually infrared (IR)) to emission in the visible (VIS) range. In order to obtain efficiently emitting nanomaterials, proper amounts of rare-earth (RE) elements need to be doped into matrices with low phonon energies. NaGd 0.78-x F 4 :Yb 0.2 /Er 0.02 /Cr x 3+ nanoparticles were synthesized via thermal decomposition method. By varying concentration of Cr 3+ a series of nanomaterials with composition of NaGd 0.78-x F 4 :Yb 0.2 /Er 0.02 /Cr x 3+ were synthesized and characterized. Addition of Cr 3+ ions impacts UC emission due to possible energy migration and relaxation pathways in Yb 3+ −Er 3+ −Cr 3+ system. Effective energy difference was calculated from temperature dependent luminescence measurements of thermally coupled 2 H 11/2 and 4 S 3/2 levels. Values of calculated relative sensitivity (S r  = 1.12% K −1 ) in NaGdF 4 :Yb 3+ /Er 3+ compound were slightly higher comparing to NaGd 0.78-x F 4 :Yb 0.2 /Er 0.02 /Cr x 3+ samples; therefore, both systems could be considered for a possible application in luminescent temperature sensors.