Despite advances in the multicolor luminescence of Ce-activated materials, achieving efficient and stable near-ultraviolet (n-UV) emission remains a critical challenge. On the basis of structural rigidity engineering, a small Stokes shift (ΔS = 0.53 eV) of Ce in microwave-hydrothermally synthesized NaSrY(PO₄)₂ (NSYP) nanophosphors is achieved, addressing this shortage. The internal quantum efficiency reaches as high as 98.5% (λ_ex = 325 nm) along with superior thermostability (78% intensity retention at 423 K) and exceptional solvent resistance (82% after 10 days of immersion). The optimal nanomaterial is used as a scintillation screen for X-ray imaging, achieving a high spatial resolution of 11.0 lp/mm and clear imaging of measured objects, rivaling a commercial scintillator (CsI:Tl). A high relative sensitivity (S_R-max = 0.94 (%)·K⁻¹) is achieved for excitation intensity ratio (EIR) technology-based optical thermometry. This work presents fascinating applications in X-ray imaging and optical thermometry for n-UV-emitting nanophosphors. These findings also highlight the critical role of host structure in designing high-quality Ce-activated optical materials.