Upconversion NIR luminescence negative thermal quenching and temperature sensing in LiYGeO4:Yb3+/Nd3+ phosphors

Solid state reaction was used to create LiYGeO4(LYG):Yb3+/Nd3+ phosphors, and upconversion luminescence (UCL) properties were investigated under 980 nm laser stimulation. When only the Yb3+ concentration is altered, and the doping concentration of Nd3+ is kept at 0.02, LYG:0.30 Yb3+/0.02Nd3+ achieves the highest UCL intensity. Because to phonon-assisted transitions and electron thermal migration, considerable near infrared (NIR) UCL negative thermal quenching (NTQ) from Nd3+ is observed with rising sample temperature. The UCL intensity of 4F7/2/4S3/2 → 4I9/2 transition in LYG:0.20 Yb3+/0.02Nd3+ at 723 K is 301.39 times than that at 303 K, and the total UCL intensity of 4F7/2/4S3/2; 4F5/2/2H9/2; 4F3/2 → 4I9/2 transitions attain 24.32 times. Moreover, the temperature sensitive characteristic based on the technology using luminescence intensity ratio (LIR) was systematically evaluated. According to the study, LYG:Yb3+/Nd3+ phosphors exhibit a remarkable NIR UCL NTQ effect and a relative temperature sensitivity (Sr) reaches 1.41% K−1, making them appropriate for application as a photothermal thermometer under high temperature.