Color-Tunable and White Luminescence Properties via Energy Transfer in Single-Phase KNaCa₂(PO₄)₂:A (A = Ce³⁺, Eu²⁺, Tb³⁺, Mn²⁺, Sm³⁺) Phosphors

A series of single-phase phosphors based on KNaCa₂(PO₄)₂ (KNCP):A (A = Ce³⁺, Eu²⁺, Tb³⁺, Mn²⁺, Sm³⁺) have been prepared via the Pechini-type sol–gel method. Photoluminescence (PL) and cathodoluminescence (CL) properties of Ce³⁺-, Eu²⁺-, Tb³⁺-, Mn²⁺-, and Sm³⁺-activated KNCP phosphors were investigated. For the A singly doped KNCP samples, they exhibit the characteristic emissions of the A activator. Na⁺ ions exhibit the best charge compensation result among Li⁺, Na⁺, and K⁺ ions for Ce³⁺-, Tb³⁺-, and Sm³⁺-doped KNCP samples. The energy transfers from Ce³⁺ to Tb³⁺ and Mn²⁺ ions as well as Eu²⁺ to Tb³⁺ and Mn²⁺ have been validated. The emission colors of KNCP:Ce³⁺/Eu²⁺, Tb³⁺/Mn²⁺, Na⁺ samples can be adjusted by energy transfer process and changing the Tb³⁺/Mn²⁺ concentration. More importantly, white light emission in KNCP:Eu²⁺, Mn²⁺ system has been obtained. The KNCP:Tb³⁺, Na⁺ sample shows tunable luminescence from blue to cyan and then to green with the change of Tb³⁺ concentration due to the cross-relaxation from ⁵D₃ to ⁵D₄. A white emission can also be realized in the single-phase KNCP host by reasonably adjusting the doping concentrations of Tb³⁺ and Sm³⁺ (reddish-orange emission) under low-voltage electron beam excitation. Additionally, the temperature-dependent PL properties of as-prepared phosphors reveal that the KNCP host has good thermal stability. Therefore, the KNCP:A (A = Ce³⁺, Eu²⁺, Tb³⁺, Mn²⁺, Sm³⁺) phosphors could be regarded as good candidates for UV W-LEDs and FEDs

Oxonitridosilicate Y₁₀(Si₆O₂₂N₂)O₂:Ce³⁺,Mn²⁺ Phosphors: A Facile Synthesis via the Soft-Chemical Ammonolysis Process, Luminescence, and Energy-Transfer Properties

Ce³⁺- and/or Mn²⁺-activated Y₁₀(Si₆O₂₂N₂)­O₂ phosphors have been prepared via a soft-chemical ammonolysis method. Structure refinement, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared, and thermogravimetry analysis have been employed to characterize the phase purity, crystal structure, morphology, crystallization condition, chemical composition, and thermal stability of the products. The photoluminescence and cathodoluminescence properties for Ce³⁺- and Mn²⁺-doped Y₁₀(Si₆O₂₂N₂)­O₂ phosphors were studied in detail. For Ce³⁺/Mn²⁺ singly doped Y₁₀(Si₆O₂₂N₂)­O₂ phosphors, typical emissions of Ce³⁺ (blue) and Mn²⁺ (reddish-orange) ions can be observed. Especially, Ce³⁺ emission at different lattice sites 4f and 6h has been identified and discussed. Energy transfer from Ce³⁺(I) and Ce³⁺(II) to Mn²⁺ ions in Y₁₀(Si₆O₂₂N₂)­O₂:Ce³⁺,Mn²⁺ samples has been validated and confirmed by the photoluminescence spectra and luminescence decay times. A color-tunable emission in Y₁₀(Si₆O₂₂N₂)­O₂:Ce³⁺,Mn²⁺ phosphors can be achieved by an energy-transfer process and a change in the doping concentration of the activators. The temperature-dependent photoluminescence properties and degradation property of cathodoluminescence under continuous electron bombardment of as-synthesized phosphors prove that the Y₁₀(Si₆O₂₂N₂)­O₂ host has good stability. Therefore, the Y₁₀(Si₆O₂₂N₂)­O₂:Ce³⁺,Mn²⁺ phosphors may potentially serve as single-phase blue/reddish-orange phosphors for white-light-emitting diodes and field-emission displays

Hydrothermal Derived LaOF:Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) Nanocrystals with Multicolor-Tunable Emission Properties

A series of LaOF:Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) nanocrystals with good dispersion have been successfully prepared by the hydrothermal method followed a heat-treatment process. Under ultraviolet radiation and low-voltage electron beam excitation, the LaOF:Ln³⁺ nanocrystals show the characteristic f-f emissions of Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, or Ho) and give red, blue-green, orange, yellow, blue, and green emission, respectively. Moreover, there exists simultaneous luminescence of Tb³⁺, Eu³⁺, Sm³⁺, Dy³⁺, Tm³⁺, or Ho³⁺ individually when codoping them in the single-phase LaOF host (for example, LaOF:Tb³⁺, Eu³⁺/Sm³⁺; LaOF:Tm³⁺, Dy³⁺/Ho³⁺; LaOF:Tm³⁺, Ho³⁺, Eu³⁺ systems), which is beneficial to tune the emission colors. Under low-voltage electron beam excitation, a variety of colors can be efficiently adjusted by varying the doping ions and the doping concentration, making these materials have potential applications in field-emission display devices. More importantly, the energy transfer from Tm³⁺ to Ho³⁺ in the LaOF:Tm³⁺, Ho³⁺ samples under UV excitation was first investigated and has been demonstrated to be a resonant type via a quadrupole-quadrupole mechanism. The critical distance (<i>R</i>_Tm–Ho) is calculated to be 28.4 Å. In addition, the LaOF:Tb³⁺ and LaOF:Tm³⁺ phosphors exhibit green and blue luminescence with better chromaticity coordinates, color purity, and higher intensity compared with the commercial green phosphor ZnO:Zn and blue phosphor Y₂SiO₅:Ce³⁺ to some extent under low-voltage electron beam excitation

Luminescence and Energy Transfer Properties of Ca₂Ba₃(PO₄)₃Cl and Ca₂Ba₃(PO₄)₃Cl:A (A = Eu²⁺/Ce³⁺/Dy³⁺/Tb³⁺) under UV and Low-Voltage Electron Beam Excitation

Pure Ca₂Ba₃(PO₄)₃Cl and rare earth ion (Eu²⁺/Ce³⁺/Dy³⁺/Tb³⁺) doped Ca₂Ba₃(PO₄)₃Cl phosphors with the apatite structure have been prepared via a Pechini-type sol–gel process. X-ray diffraction (XRD) and structure refinement, photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, absolute quantum yield, as well as lifetimes were utilized to characterize samples. Under UV light excitation, the undoped Ca₂Ba₃(PO₄)₃Cl sample shows broad band photoluminescence centered near 480 nm after being reduced due to the defect structure. Eu²⁺ and Ce³⁺ ion doped Ca₂Ba₃(PO₄)₃Cl samples also show broad 5d → 4f transitions with cyan and blue colors and higher quantum yields (72% for Ca₂Ba₃(PO₄)₃Cl:0.04Eu²⁺; 67% for Ca₂Ba₃(PO₄)₃Cl:0.016Ce³⁺). For Dy³⁺ and Tb³⁺ doped Ca₂Ba₃(PO₄)₃Cl samples, they give strong line emissions coming from 4f → 4f transitions. Moreover, the Ce³⁺ ion can transfer its energy to the Tb³⁺ ion in the Ca₂Ba₃(PO₄)₃Cl host, and the energy transfer mechanism has been demonstrated to be a resonant type, via a dipole–quadrupole interaction. However, under the low voltage electron beam excitation, Tb³⁺ ion doped Ca₂Ba₃(PO₄)₃Cl samples present different luminescence properties compared with their PL spectra, which is ascribed to the different excitation mechanism. On the basis of the good PL and CL properties of the Ca₂Ba₃(PO₄)₃Cl:A (A = Ce³⁺/Eu²⁺/Tb³⁺/Dy³⁺), Ca₂Ba₃(PO₄)₃Cl might be promising for application in solid state lighting and field-emission displays

Tunable Luminescence and Energy Transfer properties of Sr₃AlO₄F:RE³⁺ (RE = Tm/Tb, Eu, Ce) Phosphors

Sr3AlO4F:RE3+ (RE = Tm/Tb, Eu, Ce) phosphors were prepared by the conventional solid-state reaction. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectra, as well as lifetimes were utilized to characterize samples. Under the excitation of UV light, Sr3AlO4F:Tm3+, Sr3AlO4F:Tb3+, and Sr3AlO4F:Eu3+ exhibit the characteristic emissions of Tm3+ (1D2→3F4, blue), Tb3+ (5D4→7F5, green), and Eu3+ (5D0→7F2, red), respectively. By adjusting the doping concentration of Eu3+ ions in Sr3AlO4F:0.10Tm3+, 0.10Tb3+, zEu3+, a white emission in a single composition was obtained under the excitation of 360 nm, in which an energy transfer from Tb3+ to Eu3+ was observed. For Sr3AlO4F:Ce3+,Tb3+ samples, the energy transfer from Ce3+ to Tb3+ is efficient and demonstrated to be a resonant type via a dipole–quadrupole interaction by comparing the experimental data and theoretical calculation. Furthermore, the critical distance of the Ce3+ and Tb3+ ions has also been calculated to be 9.05 Å. The corresponding luminescence and energy transfer mechanisms have been proposed in detail. These phosphors might be promising for use in near-UV LEDs

Color-Tunable Emission and Energy Transfer in Ca₃Gd₇(PO₄)(SiO₄)₅O₂: Ce³⁺/Tb³⁺/Mn²⁺ Phosphors

Ce³⁺-, Tb³⁺-, and Mn²⁺-activated Ca₃Gd₇(PO₄)­(SiO₄)₅O₂ (CGPS) silicate–phosphate oxyapatite phosphors have been prepared via conventional solid-state reaction processes. The Ce³⁺ emission at different lattice sites has been identified and discussed. The dual energy transfer of Ce³⁺ → Tb³⁺ and Ce³⁺ → Mn²⁺ has been investigated. The energy transfer from Ce³⁺ to Mn²⁺ in CGPS phosphors has been demonstrated to be a resonant type via a dipole–quadrupole mechanism, and the critical distances (<i>R</i>_C) for Ce³⁺ to Mn²⁺ calculated by the concentration quenching and spectral overlap methods are 9.71 and 9.15 Å, respectively. A color-tunable emission in CGPS phosphors can be realized by Ce³⁺ → Tb³⁺ or Ce³⁺ → Mn²⁺ energy transfer. CGPS:0.05Ce³⁺/ 0.15Tb³⁺ shows the optimum green emission. Meanwhile, white cathodoluminescence (CL) has been realized in a single-phased Ca₃Gd₇(PO₄)­(SiO₄)₅O₂ host by codoping with Ce³⁺ and Mn²⁺ with CIE (0.322, 0.326). Furthermore, the CL properties of CGPS:Ce³⁺/Tb³⁺/Mn²⁺ phosphors, including the dependence of the CL intensity on the accelerating voltage and filament current, the decay behavior of the CL intensity under electron bombardment, and the stability of the CIE chromaticity coordinates, have been investigated in detail. Because of the good CL properties and good CIE chromaticity coordinates, the as-prepared phosphors have potential application in field emission display devices

Single-Composition Trichromatic White-Emitting Ca₄Y₆(SiO₄)₆O: Ce³⁺/Mn²⁺/Tb³⁺ Phosphor: Luminescence and Energy Transfer

A series of Ca4Y6(SiO4)6O (CYS): Ce3+/Mn2+/Tb3+ oxyapatite phosphors were prepared via high-temperature solid-state reaction. Under UV excitation, there exist dual energy transfers (ET), i.e., Ce3+→Mn2+ and Ce3+→Tb3+ in the CYS: Ce3+, Mn2+, Tb3+ system and their emitting colors can be adjusted from blue to orange-red via ET of Ce3+→Mn2+ and from blue to green via ET of Ce3+→Tb3+, respectively. Moreover, a wide-range-tunable white light emission with high quantum yields (13%-30%) were obtained by precisely controlling the contents of Ce3+, Mn2+ and Tb3+ ions. On the other hand, the CL properties of CYS: Ce3+, Mn2+, Tb3+ phosphors have been investigated in detail. The studied results indicate that the as-prepared CYS: Ce3+, Mn2+, Tb3+ phosphors have good CL intensity and CIE color coordinate stability with a color-tunable emission crossing the whole white light region under low-voltage electron beam excitation. In general, the white light with varied hues has been obtained in Ce3+, Mn2+, and Tb3+-triactivated CYS phosphors by utilizing the principle of energy transfer and properly designed activator contents under UV (284, 358 nm) and low-voltage (1–5 kV) electron beam excitation, which make them as a potential single-composition trichromatic white-emitting phosphor

A Double Substitution of Mg²⁺–Si⁴⁺/Ge⁴⁺ for Al₍₁₎³⁺–Al₍₂₎³⁺ in Ce³⁺-Doped Garnet Phosphor for White LEDs

The influence of Mg²⁺–Si⁴⁺/Ge⁴⁺ incorporation into Ce³⁺-doped Y₃Al₅O₁₂ garnet phosphors on the crystal structure and luminescence properties is described in this work. X-ray diffraction with Rietveld refinements, photoluminescence spectra, absolute quantum yield, thermal quenching behavior, and lifetimes were utilized to characterize samples. The introduction of Mg²⁺–Si⁴⁺/Ge⁴⁺ leads to an obvious red shift of emission wavelength under the excitation of blue light, especially for the series of Mg²⁺–Si⁴⁺ substitutions, which is suited for white light-emitting diodes (LEDs) with low color temperatures and good color rendering using only a single phosphor. More interestingly, an additional emission band locating at high-energy was observed with ultraviolet excitation, which is different than previous literature. Under the excitation of ultraviolet, the emission color for the Mg²⁺–Si⁴⁺ substitutions can be tuned from yellow-green to blue, which is expected to obtain single-phased phosphors with white emission excited with UV-LED chip. The usual Ce³⁺ emission band at low energy has stronger quenching at high temperatures. The mechanisms for the observed phenomena are discussed

Synthesis, Luminescence, and Energy-Transfer Properties of β‑Na₂Ca₄(PO₄)₂(SiO₄):A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) Phosphors

A series of β-Na₂Ca₄(PO₄)₂(SiO₄) (β-NCPS):A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) phosphors were prepared via a high-temperature solid-state reaction route. The X-ray diffraction, Fourier transform infrared, photoluminescence (PL), cathodoluminescence (CL) properties, fluorescent lifetimes, and absolute quantum yield were exploited to characterize the samples. Under UV radiation, the β-NCPS:Eu²⁺ phosphors present bright green emissions, and the β-NCPS:Ce³⁺ phosphors show strong blue emissions, which are attributed to their 4f⁶5d¹ → 4f⁷ and 5d–4f allowed transitions, respectively. The β-NCPS:Ce³⁺, Tb³⁺ phosphors display intense tunable color from blue to green and high absolute quantum yields (81% for β-NCPS:0.12Ce³⁺ and 83% for β-NCPS:0.12Ce³⁺, 0.08Tb³⁺) when excited at 365 nm. Simultaneously, the energy transfer from Ce³⁺ to Tb³⁺ ions is deduced from the spectral overlap between Ce³⁺ emission and Tb³⁺ excitation spectra and demonstrated by the change of emission spectra and decay lifetimes. Moreover, the energy-transfer mechanism from Ce³⁺ to Tb³⁺ ions is confirmed to be exchange interaction according to the discussion of expression from Dexter and Reisfeld. Under a low-voltage electron-beam excitation, the β-NCPS:A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) phosphors exhibit their characteristic emissions, and the emission profiles of β-NCPS:Ce³⁺,Tb³⁺ phosphors are obviously different from those of the PL spectra; this difference might be ascribed to their different luminescence mechanisms. These results in PL and CL properties suggest that β-NCPS:A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) phosphors are potential candidates for solid-state lighting and field-emission displays

Color Tuning Luminescence of Ce³⁺/Mn²⁺/Tb³⁺-Triactivated Mg₂Y₈(SiO₄)₆O₂ via Energy Transfer: Potential Single-Phase White-Light-Emitting Phosphors

Ce³⁺, Mn²⁺, and Tb³⁺-activated Mg₂Y₈(SiO₄)₆O₂ (MYS) oxyapatite phosphors have been prepared via solid state reaction process. The Ce³⁺ emission at different lattice sites in MYS host has been identified and discussed. Under UV excitation, there exist dual energy transfers (ET), that is, Ce³⁺ → Mn²⁺ and Ce³⁺ → Tb³⁺ in the MYS: Ce³⁺/Mn²⁺/Tb³⁺ system. The energy transfer from Ce³⁺ to Mn²⁺ in MYS: Ce³⁺/Mn²⁺ phosphors has been demonstrated to be a resonant type via a dipole–quadrupole mechanism, and the critical distance (<i>R</i>_C) calculated by quenching concentration method and spectral overlap method are 10.5 and 9.7 Å, respectively. The emitting colors of MYS: Ce³⁺/Mn²⁺/Tb³⁺ samples can be adjusted from blue to orange-red via ET of Ce³⁺ → Mn²⁺ and from blue to green via ET of Ce³⁺ → Tb³⁺, respectively. More importantly, a wide-range-tunable white light emission with high quantum yields (37–47%) were obtained by precise control of the contents of Ce³⁺, Mn²⁺, and Tb³⁺ ions. On the other hand, the CL properties of MYS: Ce³⁺/Mn²⁺/Tb³⁺ phosphors have been investigated in detail. The results indicate that the as-prepared MYS: Ce³⁺/Mn²⁺/Tb³⁺ phosphors have good CL intensity and CIE coordinate stability with a color-tunable emission crossing the whole visible light region under low-voltage electron beam excitation. In conclusion, the white light with varied hues has been obtained in Ce³⁺, Mn²⁺ and Tb³⁺-activated MYS phosphors by utilizing the principle of energy transfer and properly designed activator contents as well as the select of excitation wavelength under UV and low-voltage electron beam excitation