Upconversion luminescence thermal enhancement from visible to near infrared and improving temperature sensitivity under high temperature using a second-harmonic generation response

Er3+/Nd3+ co-doped and Er3+/Yb3+/Nd3+ triple-doped Cs2Bi2Sr(P2O7)(PO4)2 (CBSP) phosphors are prepared by a solid state reaction, and upconversion luminescence (UCL) from visible to near infrared was investigated under 808, 980, and 1550 nm laser excitation, respectively. UCL of Er3+ and Nd3+ manifests thermal enhancement under 808, 980, and 1550 nm excitation, respectively, except for under 980 nm laser excitation, the Er3+/Nd3+ co-doped sample exhibits UCL thermal quenching of Er3+. This thermal enhancement phenomenon has been discussed and attributed to phonon-assisted energy transfer and electron thermal migration. The relative temperature sensitivities were calculated based on an luminescence intensity ratio technique under 980 and 1550 nm laser excitation, respectively. Under the 1550 nm laser excitation, using a second-harmonic generation response improved the temperature sensitivity in a high temperature range, and the two maximum sensitivities at low and high temperature are obtained as 0.0062 K−1 at 484 K and 0.0111 K−1 at 697 K; 0.0219 K−1 at 303 K and 0.0097 K−1 at 555 K for the Er3+/Nd3+ co-doped and Er3+/Yb3+/Nd3+ triple-doped samples, respectively. UCL thermal enhancement and using a second-harmonic generation response provide a new approach for improving the sensitivity as an optical thermometer under high temperature.