Investigation of the sensitization effect of Yb3+ in Yb, Er co-doped Sr5(PO4)3F transparent ceramics: From single-band red upconversion to temperature sensing behavior

Lanthanide-ion-doped red upconversion (UC) fluorescent materials with excellent signal-to-noise ratio, stability, and red-green luminous intensity ratio have proven of tremendous research importance for biomedical, three-dimensional (3D) displays, sensors, and other sectors. In this study, xYb, 1Er: Sr5(PO4)3F (S-FAP) (x=0-5 at.%) transparent ceramics with outstanding optical quality were fabricated by hot pressing the co-precipitation powder with high sintering activity. The energy dispersive X-ray (EDX) results showed that the trivalent lanthanide ions were evenly doped into the S-FAP ceramic lattice. Increased Yb3+ doping considerably restricted the growth of ceramic grain size, which should be attributable to a decrease in sintering activity under high Yb doping conditions. The co-doping of Yb3+ successfully resulted in a significant improvement in up/down conversion efficiency via effective energy transfer mechanisms and the optimization of the electron population at the energy level of red-green emission. Furthermore, single-band red upconversion luminescence with the greatest red-green upconversion luminescence integral intensity ratio of 125.74 was discovered under 980 nm laser pumping at room temperature. The energy transition process involved in the phenomenon of the up-conversion luminescence intensity shift of red-green emission has been thoroughly examined. Finally, the noncontact optical thermometric ability based on fluorescence intensity ratio (FIR) technology showed that the maximum absolute sensitivity (Sa) of the 5Yb1Er sample in the temperature range of 320-556 K is 1.1×10-3 K-1, implying the possible use of Yb/Er-doped S-FAP transparent ceramics in the field of optical thermometers.