Dongling Geng

Tunable luminescence of Ce3+/Mn2+-coactivated Ca2Gd8(SiO4)6O2 through energy transfer and modulation of excitation: potential single-phase white/yellow-emitting phosphors

Ce3+/Mn2+-coactivated Ca2Gd8(SiO4)6O2 (CGS) oxyapatite phosphors have been prepared via high temperature solid state reaction process. The Ce3+ emission at different lattice sites has been identified and discussed. The energy transfer from Ce3+ to Mn2+ in CGS:Ce3+/Mn2+ phosphors has been validated and demonstrated to be a resonant type via a dipole-quadrupole mechanism, and the critical distance (RC) calculated by quenching concentration method and spectral overlap method are 9.4 A and 9.2 A, respectively. A color-tunable emission in CGS:Ce3+/Mn2+ phosphors can be realized by the modulation of excitation wavelengths, namely, the change of Ce3+ emission at different lattice sites and the relative PL intensity of Ce3+ and Mn2+. In addition, the cathodoluminescence (CL) properties of CGS:Ce3+/Mn2+ phosphors including the CL spectra, the dependence of CL intensity on accelerating voltage and filament current, the decay behavior of CL intensity under electron bombardment, and the stability of CIE chromaticity coordinate have been investigated in detail. The results indicate that the as-prepared CGS:Ce3+/Mn2+ phosphors have a good CL intensity stability and CIE coordinate stability with a color-tunable emission from blue to yellow, crossing the white area by the energy transfer from Ce3+ to Mn2+ under low-voltage electron beam excitation. In conclusion, the wide-ranged white light with varied hues have been obtained in Ce3+ and Mn2+ coactivated CGS phosphors by utilizing the principle of energy transfer and properly designed activator contents as well as the selection of excitation wavelength under UV (287–352 nm) and low-voltage (1–7 kV) electron beam excitation. Therefore, the CGS:Ce3+/Mn2+ phosphors may potentially be used as single-phased white/yellow-emitting phosphor for UV LEDs (light emitting diodes) and FEDs (field emission displays).

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

A series of Ca(4)Y(6)(SiO(4))(6)O (CYS): Ce(3+)/Mn(2+)/Tb(3+) oxyapatite phosphors were prepared via high-temperature solid-state reaction. Under UV excitation, there exist dual energy transfers (ET), i.e., Ce(3+)→Mn(2+) and Ce(3+)→Tb(3+) in the CYS: Ce(3+), Mn(2+), Tb(3+) system and their emitting colors can be adjusted from blue to orange-red via ET of Ce(3+)→Mn(2+) and from blue to green via ET of Ce(3+)→Tb(3+), respectively. Moreover, a wide-range-tunable white light emission with high quantum yields (13%-30%) were obtained by precisely controlling the contents of Ce(3+), Mn(2+) and Tb(3+) ions. On the other hand, the CL properties of CYS: Ce(3+), Mn(2+), Tb(3+) phosphors have been investigated in detail. The studied results indicate that the as-prepared CYS: Ce(3+), Mn(2+), Tb(3+) 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 Ce(3+), Mn(2+), and Tb(3+)-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.

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

Sr(3)AlO(4)F:RE(3+) (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, Sr(3)AlO(4)F:Tm(3+), Sr(3)AlO(4)F:Tb(3+), and Sr(3)AlO(4)F:Eu(3+) exhibit the characteristic emissions of Tm(3+) ((1)D(2)→(3)F(4), blue), Tb(3+) ((5)D(4)→(7)F(5), green), and Eu(3+) ((5)D(0)→(7)F(2), red), respectively. By adjusting the doping concentration of Eu(3+) ions in Sr(3)AlO(4)F:0.10Tm(3+), 0.10Tb(3+), zEu(3+), a white emission in a single composition was obtained under the excitation of 360 nm, in which an energy transfer from Tb(3+) to Eu(3+) was observed. For Sr(3)AlO(4)F:Ce(3+),Tb(3+) samples, the energy transfer from Ce(3+) to Tb(3+) 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 Ce(3+) and Tb(3+) 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 tuning via energy transfer in Sr3In(PO4)(3):Ce3+/Tb3+/Mn2+ phosphors

Sr3In(PO4)3 (SIP):Ce3+/Tb3+/Mn2+ phosphors have been prepared via a solid state reaction process. Under UV excitation, there are three energy transfer (ET) pairs in the SIP host, i.e., Ce3+ → Tb3+, Ce3+ → Mn2+, and Tb3+ → Mn2+. Both of the ETs from Ce3+ to Tb3+ and from Ce3+ to Mn2+ in the SIP host have been demonstrated to be resonant type via a dipole–quadrupole mechanism, and the critical distance (RC) calculated by the quenching concentration method and spectral overlap method, respectively, were investigated. By the ET of Ce3+ → Tb3+, Ce3+ → Mn2+, and Tb3+ → Mn2+ the emitting colors of the studied samples could be adjusted from blue to green, from blue to orange-red, and from green to green-yellow, respectively. More importantly, under low-voltage electron beam excitation, the CL spectra of the SIP:Ce3+, Mn2+ samples cover the whole visible light region, resulting in a white light emission. Additionally, the CL properties of SIP:Ce3+/Tb3+/Mn2+ phosphors have been investigated in detail. The results reveal that the as-prepared phosphors have good CL intensity and CIE coordinate stability under electron beam bombardment. Compared with the commercial green phosphor ZnO:Zn, SIP:7% Ce3+, the 10% Tb3+ sample has a higher CL brightness. In conclusion, tunable light with high quantum yield (68%) has been obtained in SIP:Ce3+/Tb3+/Mn2+ phosphors by utilizing the principle of energy transfer and properly selecting the activator contents under UV and electron beam excitation.

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

A series of LaOF:Ln(3+) (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:Ln(3+) nanocrystals show the characteristic f-f emissions of Ln(3+) (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 Tb(3+), Eu(3+), Sm(3+), Dy(3+), Tm(3+), or Ho(3+) individually when codoping them in the single-phase LaOF host (for example, LaOF:Tb(3+), Eu(3+)/Sm(3+); LaOF:Tm(3+), Dy(3+)/Ho(3+); LaOF:Tm(3+), Ho(3+), Eu(3+) 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 Tm(3+) to Ho(3+) in the LaOF:Tm(3+), Ho(3+) samples under UV excitation was first investigated and has been demonstrated to be a resonant type via a quadrupole-quadrupole mechanism. The critical distance (R(Tm-Ho)) is calculated to be 28.4 Å. In addition, the LaOF:Tb(3+) and LaOF:Tm(3+) 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 Y(2)SiO(5):Ce(3+) to some extent under low-voltage electron beam excitation.

Nanocrystalline CaYAlO4:Tb3+/Eu3+ as promising phosphors for full-color field emission displays.

Eu(3+) and/or Tb(3+)-doped CaYAlO(4) phosphor samples were synthesized by Pechini-type sol-gel method. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. For CaYAlO(4):Tb(3+), it is shown that the Tb(3+)-doping concentration has a significant effect on the (5)D(3)/(5)D(4) emission intensity of Tb(3+), which is attributed to the cross relaxation from (5)D(3) to (5)D(4). Under the 4f(8)→ 4f(7)5d excitation of Tb(3+) or low-voltage electron beams excitation, the CaYAlO(4):Tb(3+) phosphors show tunable luminescence from blue to cyan, and then to green with the change of Tb(3+)-doping concentration. The CaYAlO(4):Eu(3+) samples exhibit a reddish-orange emission of Eu(3+) corresponding to (5)D(0,1)→(7)F(0,1,2,3) transitions. Furthermore, a white emission can be realized in the single phase CaYAlO(4) host by reasonably adjusting the doping concentrations of Tb(3+) and Eu(3+) under low-voltage electron beams excitation. Compared with the commercial blue (Y(2)SiO(5):Ce(3+)) and green (ZnO:Zn) phosphors, CaYAlO(4):0.1%Tb(3+) and CaYAlO(4):5%Tb(3+) phosphors have higher CL intensity and stability under continuous electron bombardment. Due to the excellent CL properties and good CIE chromaticity coordinates, the as-prepared Tb(3+)/Eu(3+)-doped CaYAlO(4) nanocrystalline phosphors have potential application in FEDs devices.

Color-tunable emission and energy transfer in Ca3Gd7(PO4)(SiO4)5O2: Ce3+/Tb3+/Mn2+ phosphors.

Ce(3+)-, Tb(3+)-, and Mn(2+)-activated Ca(3)Gd(7)(PO(4))(SiO(4))(5)O(2) (CGPS) silicate-phosphate oxyapatite phosphors have been prepared via conventional solid-state reaction processes. The Ce(3+) emission at different lattice sites has been identified and discussed. The dual energy transfer of Ce(3+) → Tb(3+) and Ce(3+) → Mn(2+) has been investigated. The energy transfer from Ce(3+) to Mn(2+) in CGPS phosphors has been demonstrated to be a resonant type via a dipole-quadrupole mechanism, and the critical distances (R(C)) for Ce(3+) to Mn(2+) 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 Ce(3+) → Tb(3+) or Ce(3+) → Mn(2+) energy transfer. CGPS:0.05Ce(3+)/ 0.15Tb(3+) shows the optimum green emission. Meanwhile, white cathodoluminescence (CL) has been realized in a single-phased Ca(3)Gd(7)(PO(4))(SiO(4))(5)O(2) host by codoping with Ce(3+) and Mn(2+) with CIE (0.322, 0.326). Furthermore, the CL properties of CGPS:Ce(3+)/Tb(3+)/Mn(2+) 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.

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 (Eu(2+)/Ce(3+)/Dy(3+)/Tb(3+)) 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. Eu(2+) and Ce(3+) 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:0.04Eu(2+); 67% for Ca2Ba3(PO4)3Cl:0.016Ce(3+)). For Dy(3+) and Tb(3+) doped Ca2Ba3(PO4)3Cl samples, they give strong line emissions coming from 4f → 4f transitions. Moreover, the Ce(3+) ion can transfer its energy to the Tb(3+) 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, Tb(3+) 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 = Ce(3+)/Eu(2+)/Tb(3+)/Dy(3+)), Ca2Ba3(PO4)3Cl might be promising for application in solid state lighting and field-emission displays.

Tunable luminescence and energy transfer properties of Ca5(PO4)2SiO4:Ce3+/Tb3+/Mn2+ phosphors

A series of single-composition phosphors Ca5(PO4)2SiO4:Ce3+, Tb3+, Mn2+ have been prepared via a high-temperature solid-state reaction process. The Ce3+ emission at different lattice sites has been identified and discussed. The energy transfer from Ce3+ to Tb3+ and Mn2+ ions has been validated. The emissive colors of Ca5(PO4)2SiO4:Ce3+, Tb3+/Mn2+ samples can be adjusted from blue to green and from blue to red-orange by the energy transfer of Ce3+ → Tb3+ and Ce3+ → Mn2+, respectively. More importantly, white emission has been obtained through adjusting the relative concentrations of Ce3+, Tb3+ and Mn2+ ions in the Ca5(PO4)2SiO4 host under UV and low-voltage electron beam excitation, respectively. Additionally, the temperature-dependent photoluminescence and the degradation behaviors of cathodoluminescence under continuous electron bombardment for as-prepared phosphors have been investigated in detail. The results reveal that the Ca5(PO4)2SiO4 host is stable enough to protect the photoluminescence and cathodoluminescence properties of Ce3+, Tb3+ and Mn2+ ions from being affected. Tunable luminescence and the stable structure suggest that Ca5(PO4)2SiO4:Ce3+/Tb3+/Mn2+ phosphors have great potential in the application in WLEDs and FEDs.

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 Mg(2+)-Si(4+)/Ge(4+) incorporation into Ce(3+)-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 Mg(2+)-Si(4+)/Ge(4+) leads to an obvious red shift of emission wavelength under the excitation of blue light, especially for the series of Mg(2+)-Si(4+) 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 Mg(2+)-Si(4+) 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 Ce(3+) emission band at low energy has stronger quenching at high temperatures. The mechanisms for the observed phenomena are discussed.