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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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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In this work, the crystal structure and electronic structure as well as the synchrotron radiation vacuum ultraviolet-ultraviolet-visible (VUV-UV-vis) luminescence properties of Li ₆ Y(BO ₃ ) ₃ (LYBO):Ce ³⁺ phosphors were investigated in detail. The Rietveld refinement and DFT calculation reveal the P2 ₁ /c monoclinic crystal phase and the direct band gap of the LYBO compound, respectively. Only one kind of Ce ³⁺ 4f-5d transition is resolved in terms of the low temperature VUV-UV excitation, UV-vis emission spectra and luminescence decay curves. Furthermore, by constructing the vacuum referred binding energy (VRBE) scheme and applying the frequency-degenerate vibrational model, the impacts of 5d electron binding energy and electron-phonon coupling on luminescence of Ce ³⁺ in LYBO are analysed. The results show that the Ce ³⁺ emission in LYBO possesses a moderate intrinsic thermal stability. With the increase in concentration, the thermal stability of the emission gets worse due to the possible thermally-activated concentration quenching. In addition, the simulation of Ce ³⁺ emission profile at low temperature reveals that the 4f-5d electronic transitions of Ce ³⁺ ions can be treated to couple with one frequency-degenerate vibrational mode having the effective phonon energy of ∼257 cm ⁻¹ with the corresponding Huang-Rhys parameter of ∼6, which indicates a strong electron-phonon interaction of Ce ³⁺ luminescence in the Li ₆ Y(BO ₃ ) ₃ host. Finally, the X-ray excited luminescence spectrum of the LYBO:5%Ce ³⁺ phosphor is measured to check the potential scintillator applications.

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A detailed investigation on photoluminescence properties and energy transfer (ET) dynamics of Ce³⁺, Pr³⁺-doped BaY₂Si₃O₁₀ is provided along with the potential X-ray excited luminescence application. The luminescence properties of Pr³⁺ are studied in VUV-UV-vis spectral range at low temperature, and the spectral profiles of Pr^{3+ 3}P₀ and ¹D₂ emission lines are determined using time-resolved emission spectra. Upon 230 nm excitation, the electron population from Pr³⁺ 4f5d state to its 4f² excited state is discussed in detail. As Pr³⁺ concentration rises, Pr^{3+ 3}P₀ and ¹D₂ luminescence possess different concentration-related properties. The incorporation of Ce³⁺ in the codoped sample produces the strong Ce³⁺ luminescence under 230 nm excitation, which is the combined result of Pr³⁺ 4f5d → Ce³⁺ 5d ET and Ce³⁺ intrinsic excitation. On the other hand, the increasingly strong ET of Ce³⁺ 5d → Pr³⁺ 4f² results in the decrease of Ce³⁺ emission intensity and the gradual deviation of Ce³⁺ luminescence decay from the single exponential in the system. By employing the Inokuti-Hirayama model, the dipole-dipole interaction is confirmed as the predominant multipolar effect in controlling this ET process, and the value of C_DA is determined to be 9.97 × 10^-47 m⁶·s^-1. Finally, the relatively low scintillation light yield of Ce³⁺-doped BaY₂Si₃O₁₀ material impedes its application potential in the scintillator field, and the cosubstitution of Pr³⁺ results in the observable decline of scintillation performance.

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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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RE³⁺ (RE = Pr, Sm, Tb, Er, Dy)-activated Y₄Si₂O₇N₂ samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. The absorption band located at about 250 nm is attributed to the host absorption. The 5d bands of Pr³⁺ and Tb³⁺ are at rather low energy in Y₄Si₂O₇N₂ compared to oxide. The direct Pr³⁺ 4f² → 4f¹5d¹ excitation at 275 nm leads to typical 4f² → 4f² line emissions (450–700 nm) and strong 4f¹5d¹ → 4f² broad band emission (300–450 nm), respectively. The charge transfer (N³⁻ → Sm³⁺) band of Sm³⁺ was observed at a somewhat lower energy of 4.68 eV compared to oxide, and Sm³⁺-activated sample shows a bright red emission originating from ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2 and 9/2) transitions. For Tb³⁺-doped sample, the direct Tb³⁺ 4f⁸ → 4f⁷5d¹ excitation leads to ⁵D₃ → ⁷F_J (J = 6, 5, 4, 3) (blue) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) (green) line emissions, the cross-relaxation depended on Tb concentration has happened. The incorporation of Er³⁺ (or Dy³⁺) into Y₄Si₂O₇N₂ resulted in a typical Er³⁺ (or Dy³⁺) f-f line absorptions and emissions. Moreover, the energy transfer from the host lattice to the luminescent activators (Pr³⁺, Tb³⁺ and Sm³⁺) is observed. The energy level diagram containing the position of 4f and 5d energy levels of all Ln²⁺ and Ln³⁺ ions relative to the valence and conduction band of Y₄Si₂O₇N₂ has been established and studied based on the data presented in this work, and further provides a platform for studying the photoluminescence properties as well as the valence stability of the lanthanide ions.

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A series of Ba2-xEuxMgSi2O7 phosphors was prepared by a solid-state reaction method at high temperature. The theoretical density of the optimal Ba1.93Eu0.07MgSi2O7 material was calculated from the Rietveld refinement result. Eu L3-edge X-ray absorption near edge structure (XANES) spectrum was measured to confirm the valence of Eu ions in Ba2MgSi2O7. The X-ray excited radioluminescence and the thermoluminescence after β-ray irradiation were investigated based on the VUV-vis photoluminescence. The light yield of the optimal Ba1.93Eu0.07MgSi2O7 sample under X-ray excitation was estimated to be ~29,000±6000 photons/M eV. So the temperature-dependent luminescence properties of this sample under X-ray and 344 nm excitation were further studied, and the charge traps in the scintillation process were discussed through thermoluminescence spectra. The high scintillation intensity together with an appropriate intrinsic decay time and its non-hygroscopicity endow the further optimized phosphor Ba1.93Eu0.07MgSi2O7 a promising scintillation material for X-ray detection.@en

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-5d_i (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⁺-O^2- 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.

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