Promising lanthanide-doped double molybdates KYb(MoO4)2 phosphors for highly efficient upconversion luminescence and temperature sensing

Here we report the highly efficient upconversion luminescence (UCL) and optical temperature sensing based on the novel host of KYb(MoO4)2 doped with trivalent lanthanide (Ln3+) ions at 980 nm excitation. The high Yb3+ concentration and unique ordered layer structure in KYb(MoO4)2 host are beneficial for the enhancement of UCL efficiency by improving the absorption and the negative migration of excitation energy. Ho3+, Er3+, and Tm3+ ions were selected to singly dope the KYb(MoO4)2 host, achieving three primary colors of red, green, blue UCL, respectively. At the optimal doping concentration, the blue upconversion quantum yield (UCQY) of the KYb(MoO4)2: 1.0%Tm3+ phosphor reaches 0.13%, which is rare for the Tm3+-doped oxides. By leveraging the efficient blue light, we achieved high-brightness white UCL by co-doping Ho3+ in KYb(MoO4)2: Tm3+. Furthermore, the temperature sensing performance of the KYb(MoO4)2: Tm3+, Ho3+ phosphors operating within the first biological window (BW-I) was evaluated based on a thermo-responsive fluorescence intensity ratio (FIR) of far-red to near-infrared (NIR) emission from completely separated 3F2,3/3H4 → 3H6 transitions of Tm3+. At the excitation of 980 nm, the maximum absolute and relative sensitivities were determined as 0.25 × 10-3 K−1 at 673 K and 2.84% K−1 at 303 K, respectively. These results indicate that the double alkali-rare-earth molybdate KYb(MoO4)2 can be used as a promising host to achieve highly efficient UCL and temperature sensing, suggesting potential applications in the fields of anti-counterfeiting, displays, and non-contact temperature sensors.