Improved thermometry sensitivity of red-emitting SrGd2O4:Er3+,Yb3+ phosphors using novel NTCL-FIR technology based on 2H11/2 and 4F9/2

Abstract

In this work, the upconversion luminescence (UCL) and temperature-sensing properties of SrGd2O4 phosphors doped with Er3+, Yb3+ were investigated. The UCL performance was studied by adjusting the doping concentrations of Er3+, Yb3+. It can be found that the intensity of red UCL is effectively improved by doping Yb3+ ions. The band structures of SrGd2O4, SrGd2O4:5 mol%Er3+, and SrGd2O4:5 mol%Er3+,15 mol%Yb3+ were calculated using the density functional theory (DFT) to verify the experimental results. The thermal sensitivity of SrGd2O4:5 mol%Er3+,15 mol%Yb3+ phosphors was studied using the novel fluorescence intensity ratio of non-thermally coupled energy levels (NTCL-FIR) technique based on the 2H11/2 and 4F9/2 energy levels. The analytical results reveal that the maximum values of Sr are 1.69%/K (300 K), 1.18%/K (300 K) and 1.47%/K (300 K) respectively under 915, 980 and 1550 nm excitations. The Sr values of novel NTCL-FIR are compared with that of thermal coupling of energy level (TCL) and other studies in the same field. The results show that the thermometry sensitivity of red-emitting UCL materials can be enhanced by using the novel NTCL-FIR technique. In addition, the intense red UCL of SrGd2O4:Er3+,Yb3+ phosphors have the advantage of deeply penetrating biological tissues. Therefore, the combination of novel NTCL-FIR and red-emitting SrGd2O4:Er3+,Yb3+ phosphors could be conducive to temperature monitoring in vivo.