Cationic Effects on Photo- and X-ray Radioluminescence of K 3 RE(PO 4 ) 2 :Ce 3+ /Pr 3+ (RE = La, Gd, and Y) Phosphors toward X-ray Detection.

Cationic tuning for lanthanide (Ce 3+ /Pr 3+ )-activated inorganic phosphors with stable, efficient, and fast-decay 5d-4f emissions has emerged as an important strategy toward the continuing pursuit of superior scintillators. The in-depth understanding of the cationic effects on photo- and radioluminescence of lanthanides Ce 3+ and Pr 3+ centers is requisite for the rational cationic tuning. Here, we perform a systematic study on the structure and photo- and X-ray radioluminescence properties of K 3 RE(PO 4 ) 2 :Ce 3+ /Pr 3+ (RE = La, Gd, and Y) phosphors to elucidate the underlying cationic effects on their 4f-5d luminescence. By using the Rietveld refinements, low-temperature synchrotron-radiation vacuum ultraviolet-ultraviolet spectra, vibronic coupling analyses, and vacuum-referred binding energy schemes, the origins of lattice parameter evolutions, 5d excitation energies, 5d emission energies, and Stokes shifts as well as good emission thermal stabilities of K 3 RE(PO 4 ) 2 :Ce 3+ systems are revealed. In addition, the correlations of Pr 3+ luminescence to Ce 3+ in the same sites are also discussed. Finally, the X-ray excited luminescence manifests that the K 3 Gd(PO 4 ) 2 :1%Ce 3+ sample possesses a light yield of ∼10,217 photons/MeV, indicating its potentiality toward X-ray detection application. These results deepen the understanding of cationic effects on Ce 3+ and Pr 3+ 4f-5d luminescence and inspire the inorganic scintillator development.