RbBaPO4:Eu2+ phosphors have been prepared by a high-temperature solid-state reaction method, and the structure was determined by Rietveld refinement based on powder X-ray diffraction (P-XRD) data. Their VUV-UV-vis photoluminescence properties are systematically investigated with three objectives: (1) based on low-temperature spectra, we clarify the site occupancies of Eu2+, and demonstrate that the doublet emission bands at ∼406 and ∼431 nm originate from Eu2+ in Ba2+ [Eu2+(I)] and Rb+ [Eu2+(II)] sites, respectively; (2) an electron-vibrational interaction (EVI) analysis is conducted to estimate the Huang-Rhys factors, the zero-phonon lines (ZPLs) and the Stokes shifts of Eu2+ in Rb+ and Ba2+ sites; (3) the studies on luminescence decay of Eu2+(I) reveal that dipole-dipole interaction is mainly responsible for the energy transfer from Eu2+(I) to Eu2+(II), and the energy migration between Eu2+(I) is weak. Finally, the X-ray excited luminescence (XEL) spectrum indicates that the light yield of the sample RbBa0.995Eu0.005PO4 is ∼17700 ph/MeV, showing its potential application in X-ray detecting.

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Tuning of phosphor luminescence properties, including the emission energy/intensity and thermal stability, is an important way to develop superior luminescent materials for diverse applications. In this work, we discuss the effect of band gap engineering and energy transfer on the luminescence properties of Ce³⁺ or Pr³⁺ doped (Y,Gd)AGG systems, and analyze the underlying reasons for their different phenomena. By using VUV-UV excitation spectra and constructing VRBE schemes, the changes of host band structure, 5d excited level energies and emission thermal stability of Ce³⁺ and Pr³⁺ with the incorporation of Gd³⁺ ions were studied. In addition, the energy transfer dynamics was also investigated in terms of the luminescence decay curves. This work demonstrates a way to tune phosphor luminescence properties by combining band gap engineering and energy transfer tailoring and provides an inspiring discussion on the different results of Gd³⁺ doping on the Ce³⁺ and Pr³⁺ emissions.

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A series of Ln-doped KSrPO₄ (Ln = Ce³⁺, Eu³⁺, Eu²⁺, Pr³⁺) phosphors are prepared through a high-temperature solid-state method. The KSrPO₄ compound is confirmed to possess a β-K₂SO₄ structure with the Pnma group by Rietveld refinement, and the temperature-dependent lattice parameters are investigated with the powder X-ray diffraction results at different temperatures. Ce³⁺ and Eu³⁺ ions are introduced to probe the crystal field strength (CFS) and the lanthanide site symmetry by using VUV-UV-vis spectroscopy. The temperature-dependent luminescence properties of KSrPO₄: Ce³⁺/Eu²⁺ exhibit an excellent thermal stability of Ce³⁺/Eu²⁺ luminescence. Based on the VUV-UV-vis spectra of Ce³⁺ and Eu³⁺ doped KSrPO₄, the vacuum referred binding energy (VRBE) scheme is constructed to understand the redox properties of Eu, the 5d energy levels of Pr³⁺ and the thermal quenching characteristics of Ce³⁺ and Eu²⁺ luminescence.

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A series of Ce3+-doped (Ca,Sr)2Al2SiO7 phosphors with different Ce3+ and Ca2+/Sr2+ concentrations were prepared by a high temperature solid-state reaction technique. To get insight into the structure-luminescence relationship, the impact of incorporation of Sr2+ on structure of (Ca,Sr)2Al2SiO7 was first investigated via Rietveld refinement of high quality X-ray diffraction (XRD) data, and then the VUV-UV excitation and UV-vis emission spectra of (Ca,Sr)2Al2SiO7:Ce3+ were collected at low temperature. The results reveal that the crystal structure evolution of (Ca,Sr)2Al2SiO7:Ce3+ has influences on band gaps and Ce3+ luminescence properties including 4f-5di (i = 1-5) transition energies, radiative lifetime, emission intensity, quantum efficiency, and thermal stability. Moreover, the influence of Sr2+ content on the energy of Eu3+-O2- charge-transfer states (CTS) in (Ca,Sr)2Al2SiO7:Eu3+ was studied in order to construct vacuum referred binding energy (VRBE) schemes with the aim to further understand the luminescence properties of (Ca,Sr)2Al2SiO7:Ce3+. Finally, X-ray excited luminescence (XEL) spectra were measured to evaluate the possibility of (Ca,Sr)2Al2SiO7:Ce3+ as a scintillation material.@en