Simultaneous influence of Mg2+ and Sc3+ co-doping on upconversion luminescence and optical thermometry in β-NaYF4: Yb3+/Ho3+ microphosphor

Abstract

A series of xMg2+/ySc3+ co-doped β-NaYF4:0.2Yb3+/0.02Ho3+ (x = y = 0 −0.2) upconversion (UC) green phosphors are synthesized using EDTA-assisted hydrothermal method. The structure, morphology and elemental compositions are investigated in detail using different experimental techniques. The lengthwise suppression of crystal due to co-doping is associated to the kinetics involved in the crystal growth in presence of Mg2+/Sc3+. The effect of Mg2+/Sc3+ co-doping on the UC green emission of β-NaYF4:0.2Yb3+/0.02Ho3+ microphosphors is studied and about 31-fold enhancement in the green emission (5F4,5S2→5I8) is observed for the 0.08Mg2+/0.12Sc3+ co-doped phosphor. The downconversion properties of the phosphors is also discussed to showcase the dual mode luminescence. The temperature sensing performance is investigated using luminescence intensity ratio (LIR) technique for non-thermally coupled levels (5F5/5F4,5S2) of Ho3+ ions and maximum relative sensitivity of 0.258% K−1 at 374 K is obtained for the optimized phosphor. The microphosphor can be sustained at high temperature as the UC emission intensity retains about 65% and 36% at 423 K and 574 K. From chromaticity diagram, the maximum color purity of 91.37% is obtained for 0.08Mg2+/0.12Sc3+ doping concentration. The estimated thermal parameters and color purity of Mg2+/Sc3+ co-doped β-NaYF4:0.2Yb3+/0.02Ho3+ UC phosphors suggest their applicability in fabricating temperature sensors and LEDs.