Phonon‐Assisted Negative Thermal Quenching in a One‐Photon Up‐Conversion Phosphor for Thermometry

Abstract Thermal disturbance deteriorates the radiative transitions of up‐conversion phosphor, leading to decreased emission intensity at high operation temperatures. In this work, a thermal‐favored Yb 3+ /Nd 3+ co‐doped KGaGeO 4 up‐conversion phosphor with a negative thermal quenching behavior is explored. The as‐developed phosphor performs a one‐photon anti‐Stokes emission and exhibits a remarkable enhancement for the rise of ambient temperature reaching 653 K. It is demonstrated that the fascinating thermal behavior of the up‐conversion procedure is attributed to the enhanced energy transfer from the corresponding sensitizers to the activators by phonon assistance. Moreover, the microscopic dynamical process of phonon assistance and annihilation is revealed by introducing Er 3+ ions as a probe. These results not only shed light on the phonon‐assisted strategy to build a highly efficient anti‐Stokes emission system but also open prospects for constructing phonon‐favored transitions with nonthermally coupled emissions to realize luminescence thermometry for their distinct thermal responsivity.