LiNbO ₃ :Yb ³⁺ /Er ³⁺ nanocubes are synthesized by a hydrothermal method. LiNbO ₃ :Yb ³⁺ /Er ³⁺ annealed at 1050 °C exhibits a sensitivity of 0.0094 K ⁻¹ at 340 K.

The novel YbNbO₄:Er³⁺ phosphors were firstly synthesized through the hydrothermal method by adding LiOH·H₂O as flux in the H₂O/EG system. YbNbO₄:Er³⁺ phosphors showed the agglomerated irregular polygons coexisting with some tiny grains. XRD and Raman spectra were measured to understand the phase structure and the crystal growth mechanism of YbNbO₄:Er³⁺ phosphors. The upconversion (UC) emission spectra, the pump power dependency and UC mechanism were studied under 980 nm excitation. Based on the fluorescence intensity ratio technique, YbNbO₄:Er³⁺ exhibited the maximum sensor sensitivity of 0.00712 K⁻¹ at 220 K, providing a promising application in optical low-temperature sensors.

A bi-function TiO₂:Yb³⁺/Tm³⁺/Mn²⁺-assisted double-layered photoanode was designed to improve the efficiency of dye-sensitized solar cells (DSSCs). The scanning electron microscopy (SEM) results show that the introduction of Mn²⁺ ions leads to smaller-sized TiO₂:Yb³⁺/Tm³⁺/Mn²⁺ nanospheres, which is changed from nanosheet-shaped TiO₂ and TiO₂:Yb³⁺/Tm³⁺. Based on Scherrer’s formula from the X-ray diffraction (XRD) peak (101), the crystallite sizes decrease due to the introduction of Mn²⁺ ions. By utilizing screen-printing techniques, DSSCs fabricated by bi-function TiO₂:Yb³⁺/Tm³⁺/Mn²⁺-assisted double-layered photoanodes exhibit the short-circuit current density (J_sc) of 15.68 mA/cm², open-circuit voltage (V_oc) of 0.67 V, fill factor (FF) of 0.71 and the power conversion efficiency (PCE) of 7.41%. The PCE of our designed DSSC is higher than that of DSSCs with a TiO₂/TiO₂ photoanode (6.84%), which is attributed to the bi-function effects of TiO₂:Yb³⁺/Tm³⁺/Mn²⁺ including the conversion of NIR into visible light and improved light scattering. An increased charge transfer resistance of the photoanode/electrolyte interface indicates the suppressed charge recombination of electrons with the electrolyte redox couple (I⁻/I₃⁻) in DSSCs with a TiO₂/TiO₂:Yb³⁺/Tm³⁺/Mn²⁺ double-layered photoanode, which also contributes to the enhanced performance of DSSCs. The double-layered photoanode fabricated by bi-function TiO₂:Yb³⁺/Tm³⁺/Mn²⁺ nanospheres will provide a promising avenue for moving DSSCs forward to meet practical applications.