Selective thermally enhanced upconversion luminescence in Ca2Gd8Si6O26:Yb3+,Er3+ phosphors for temperature sensing

Thermally enhanced upconversion luminescence (UCL) materials have obvious advantages in the various fields of optical temperature sensing, anti-counterfeiting, and display. Here, we report a novel thermal enhancement UCL phosphor of Ca 2 Gd 8 Si 6 O 26 :Yb 3+ ,Er 3+ (CGSO:Yb 3+ ,Er 3+ ). Benefiting from the thermally enhanced phonon-assisted effect, anti-Stokes sideband excitation of Yb 3+ , energy transfer from Yb 3+ to Er 3+ , and thermal population from selective energy levels of Er 3+ are promoted with increasing temperature, which contributes to the thermal enhancement UCL of 4 F 7/2  →  4 I 15/2 , 2 H 11/2  →  4 I 15/2 , and 4 I 9/2  →  4 I 15/2 radiation transitions of Er 3+ ions. In addition, the rarely thermal enhancement of near infrared emission at 870 nm observed may be attributed to the Yb 3+ -induced effect. Furthermore, thermal quenching occurs for 4 S 3/2  →  4 I 15/2 and 4 F 9/2  →  4 I 15/2 transitions due to thermally enhanced multiphonon relaxation and thermal population. The combination of thermal enhancement and thermal quenching effect, the ratiometric optical thermometer is constructed in the wide temperature range 303–723 K by leveraging of the thermally coupled energy levels 2 H 11/2 and 4 S 3/2 of Er 3+ . This optical thermometer shows excellent temperature measurement performances with a maximum relative sensitivity of 1.1 × 10 −2  K −1  at 303 K and high repeatability of 99 %. These findings indicate that CGSO:Yb 3+ ,Er 3+ phosphors with thermally enhanced UCL have great potential application for temperature sensing.