Defect elimination to enhance photoluminescence and optical transparency of Pr-doped ceramics for self-calibrated temperature feedback windows

Pr-doped metal oxide polycrystalline transparent ceramics are highly desirable for photothermal window systems served in extreme environments; however, obtaining efficient photoluminescence (PL) together with high transparency in these ceramics is still posing serious challenges, which undoubtedly limits their applications. Here, Pr-doped Y₂Zr₂O₇ (YZO) transparent ceramics, as an illustrative example, are prepared by a solid-state reaction and vacuum sintering method. Owing to the elimination of defect clusters [ ${\text{Pr}}_{\text{Y}}^{4+}-{\text{O}}^{2-}-{\text{Pr}}_{\text{Y}}^{4+}$] and [ ${\text{Pr}}_{\text{Y}}^{4+}-{\text{e}}^{\prime }$] without the introduction of impurities and additional defects, the fabricated YZO:Pr ceramics exhibit high transparency (74%) and efficient PL (39-fold enhanced) after air annealing plus vacuum re-annealing treatment. Moreover, upon 295/450 nm excitation, the emission bands (blue, green, red, and dark red) from YZO:Pr ceramics present different temperature-dependent properties due to the thermal-quenching channel generated by the intervalence charge transfer (IVCT) state between Pr³⁺ and Zr⁴⁺ ions. Furthermore, a self-calibrated temperature feedback window with the same fluorescence intensity ratio (FIR) model (I₆₁₃/I₅₀₃, where I represents the intensity) under different excitation light sources (295 and 450 nm) is designed. The developed photothermal window operated in a wide temperature range (303–663 K) shows relatively high sensitivities (absolute sensitivity (S_a) and relative sensitivity (S_r) reach 0.008 K⁻¹ at 663 K and 0.47% K⁻¹ at 363 K, respectively), high repeatability (> 98%), and low temperature uncertainty (δT < 3.2 K). This work presents a paradigm for achieving enhanced PL along with elevated transparency of lanthanide (Ln)-doped ceramics through vacuum re-annealing treatment engineering and demonstrates their promising potential for photothermal window systems.