Dual-mode up/down-conversion optical thermometry of Pr3+-regulated Li0.9K0.1NbO3:Er3+phosphors

Photothermal sensing is crucial in developing smart wearable devices. However, designing and synthesizing luminescent materials with suitable multi -wavelength emission and constructing multiple sets of probes in a single material system is a huge challenge for constructing sensitive temperature sensors with a wide temperature range. In this paper, Pr3+ , Er3+ single -doped and double -doped Li0.9K0.1NbO3 phosphors are successfully prepared by high temperature solid phase method, and their structures, morphologies, excitation wavelengths and temperature -dependent fluorescence properties are characterized by XRD, SEM, fluorescence spectrometer and self-made heating device. Firstly, the photoluminescences of the synthesized series of samples are investigated. The results show that comparing with the single -doped Li0.9K0.1NbO3: Er3+ sample, the up/down-conversion spectra of Pr3+ , Er3+ co -doped phosphors under 808 nm/380 nm excitation show that the green fluorescence emission of Er3+ is enhanced. In addition, under 980 nm excitation, Pr3+ can effectively regulate the fluorescence energy level population pathway, so that the electrons are more effectively arranged in the 2H11/2 and 4S3/2 energy levels in the excitation process. The red emission is weakened and the green emission is enhanced, which improves the signal resolution of the fluorescent material and has a significant influence on the optical temperature measurement. Secondly, the up -conversion fluorescence property of Er3+ under 808 nm/ 980 nm laser excitation in Li0.9K0.1NbO3:Er3+ and Li0.9K0.1NbO3:Pr3+ ,Er3+ phosphors are investigated. The results show that the red and green fluorescence emissions of Er3+ are two -photon processes. Finally, the up/down-conversion dual -mode temperature sensing properties of Er3+ in Li0.9K0.1NbO3:Er3+ and Li0.9K0.1 NbO3:Pr3+ , Er3+ phosphors are investigated. It is found that both materials have good optical temperature measurement performances. The Pr3+ doping optimizes the dual -mode optical temperature measurement performances of Li0.9K0.1NbO3:Er3+ phosphors derived from the thermal coupling energy level of Er3+ ions. In addition, the up/down-conversion fluorescence mechanism of Li0.9K0.1NbO3:Er3+ and Li0.9K0.1NbO3:Er3+ , Pr3+ phosphors are proposed, and the enhanced green fluorescence by Pr3+ co -doping is attributed to the energy transfer from Pr3+ ions to Er3+ ions, leading to the increase of green fluorescence level population and the decrease of red fluorescence level population of the Er3+ ions. This new dual -mode optical temperature measurement material provides a material basis and optical temperature measurement technology for exploring other temperature measurement materials.