Blue frequency upconversion emission and optical thermometry of Ca3(PO4)2: Tm3+/Yb3+

Rhombohedral phase Ca3(PO4)2: Tm3+/Yb3+ phosphor is synthesized via hydrothermal route, and then frequency upconversion emission is studied upon 980 nm excitation. The samples have resulted strong blue emission around 472 nm and two weak emission bands at 650 and 700 nm wavelengths. The blue emission was optimized by changing the Yb3+ ion concentration, and optimum emission is observed for the sample having 0.5 mol% Tm3+ and 5 mol% Yb3+. The temperature-dependent upconversion luminescence studies were done under 980 nm excitation. The Judd–Ofelt intensity parameters were calculated using the absorption spectra and found in Ω2 > Ω4 > Ω6 order. Further temperature sensitivity of sample is explored by considering 1G4 and 3F2,3 levels as non-thermally coupled. Maximum absolute sensor sensitivity is found to be 3.63 × 10−3 K−1 at 623 K. The results indicate that Ca3(PO4)2 host is suitable for achieving intense blue upconversion emission and may be helpful for biological imaging considering the biocompatibility nature of Ca3(PO4)2.