Mengmeng Shang

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.

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.

Eu3+/Tb3+-Doped La2O2CO3/La2O3 Nano/Microcrystals with Multiform Morphologies: Facile Synthesis, Growth Mechanism, and Luminescence Properties

LaCO(3)OH nano/microcrystals with a variety of morphologies/sizes including nanoflakes, microflowers, nano/microrhombuses, two-double microhexagrams sandwichlike microspindles, and peach-nucleus-shaped microcrystals have been synthesized via a facile homogeneous precipitation route under mild conditions. A series of controlled experiments indicate that the pH values in the initial reaction systems, carbon sources, and simple ions (NH(4)(+) and Na(+)) were responsible for the shape determination of the LaCO(3)OH products. A possible formation mechanism for these products with diverse architectures has been presented. After annealing at suitable temperatures, LaCO(3)OH was easily converted to La(2)O(2)CO(3) and La(2)O(3) with the initial morphologies. A systematic study on the photoluminescence and cathodoluminescence properties of Eu(3+)- or Tb(3+)-doped La(2)O(2)CO(3)/La(2)O(3) samples has been performed in detail. The excitation and site-selective emission spectra were recorded to investigate the microstructure, site symmetry, and difference in the (5)D(0) → (7)F(2) transition of Eu(3+) ions in La(2)O(2)CO(3) and La(2)O(3) host lattices. In addition, the dependence of the luminescent intensity on the morphology for the as-prepared La(2)O(2)CO(3)/La(2)O(3):Ln(3+) (Ln = Eu, Tb) samples has been investigated. The ability of generating diverse morphologies and multiemitting colors for different rare-earth activator ion (Ln = Eu, Tb) doped La(2)O(2)CO(3)/La(2)O(3) nano/microstructures provides a great opportunity for the systematic evaluation of morphology-dependent luminescence properties, as well as the full exploration of their application in many types of color display fields.

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.

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 = Ce(3+), Eu(2+), Tb(3+), Mn(2+), Sm(3+)) have been prepared via the Pechini-type sol-gel method. Photoluminescence (PL) and cathodoluminescence (CL) properties of Ce(3+)-, Eu(2+)-, Tb(3+)-, Mn(2+)-, and Sm(3+)-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 Ce(3+)-, Tb(3+)-, and Sm(3+)-doped KNCP samples. The energy transfers from Ce(3+) to Tb(3+) and Mn(2+) ions as well as Eu(2+) to Tb(3+) and Mn(2+) have been validated. The emission colors of KNCP:Ce(3+)/Eu(2+), Tb(3+)/Mn(2+), Na(+) samples can be adjusted by energy transfer process and changing the Tb(3+)/Mn(2+) concentration. More importantly, white light emission in KNCP:Eu(2+), Mn(2+) system has been obtained. The KNCP:Tb(3+), Na(+) sample shows tunable luminescence from blue to cyan and then to green with the change of Tb(3+) concentration due to the cross-relaxation from (5)D3 to (5)D4. A white emission can also be realized in the single-phase KNCP host by reasonably adjusting the doping concentrations of Tb(3+) and Sm(3+) (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 = Ce(3+), Eu(2+), Tb(3+), Mn(2+), Sm(3+)) phosphors could be regarded as good candidates for UV W-LEDs and FEDs.

Rapid, Large-Scale, Morphology-Controllable Synthesis of YOF:Ln3+ (Ln = Tb, Eu, Tm, Dy, Ho, Sm) Nano-/Microstructures with Multicolor-Tunable Emission Properties

YOF:Ln(3+) (Ln = Tb, Eu, Tm, Dy, Ho, Sm) nano-/microstructures with a variety of novel and well-defined morphologies, including nanospheres, nanorod bundles, and microspindles, have been prepared through a convenient modified urea-based homogeneous precipitation (UBHP) technique followed by a heat treatment. The sizes and morphologies of the YOF products could be easily modulated by changing the pH values and fluoride sources. XRD, TG-DTA, FT-IR, SEM, and TEM, as well as photoluminescence (PL) and cathodoluminescence (CL) spectra, were used to characterize the prepared samples. The YOF:Ln(3+) nanospheres show the characteristic f-f transitions of Ln(3+) (Ln = Tb, Eu, Tm, Dy, Ho, Sm) ions and give bright green, red, blue, yellow, blue-green, and yellow-orange emission, respectively, under UV light and low-voltage electron beam excitation. Furthermore, YOF:0.03Tb(3+) phosphors exhibit green luminescence with superior properties in comparison with the commercial phosphor ZnO:Zn to a degree, which is advantageous for improving display quality. Because of the simultaneous luminescence of Ln(3+) in the YOF host, the luminescence colors of YOF:Ln(3+) phosphors can be precisely adjusted by changing the doped Ln(3+) ions and corresponding concentrations, which makes these materials hold great promise for applications in field-emission displays.

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 = Eu(2+), Dy(3+), Ce(3+)/Tb(3+)) 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:Eu(2+) phosphors present bright green emissions, and the β-NCPS:Ce(3+) phosphors show strong blue emissions, which are attributed to their 4f(6)5d(1) → 4f(7) and 5d-4f allowed transitions, respectively. The β-NCPS:Ce(3+), Tb(3+) phosphors display intense tunable color from blue to green and high absolute quantum yields (81% for β-NCPS:0.12Ce(3+) and 83% for β-NCPS:0.12Ce(3+), 0.08Tb(3+)) when excited at 365 nm. Simultaneously, the energy transfer from Ce(3+) to Tb(3+) ions is deduced from the spectral overlap between Ce(3+) emission and Tb(3+) excitation spectra and demonstrated by the change of emission spectra and decay lifetimes. Moreover, the energy-transfer mechanism from Ce(3+) to Tb(3+) 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 = Eu(2+), Dy(3+), Ce(3+)/Tb(3+)) phosphors exhibit their characteristic emissions, and the emission profiles of β-NCPS:Ce(3+),Tb(3+) 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 = Eu(2+), Dy(3+), Ce(3+)/Tb(3+)) phosphors are potential candidates for solid-state lighting and field-emission displays.

Oxonitridosilicate Y10(Si6O22N2)O2:Ce3+,Mn2+ phosphors: a facile synthesis via the soft-chemical ammonolysis process, luminescence, and energy-transfer properties.

Ce(3+)- and/or Mn(2+)-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 Ce(3+)- and Mn(2+)-doped Y10(Si6O22N2)O2 phosphors were studied in detail. For Ce(3+)/Mn(2+) singly doped Y10(Si6O22N2)O2 phosphors, typical emissions of Ce(3+) (blue) and Mn(2+) (reddish-orange) ions can be observed. Especially, Ce(3+) emission at different lattice sites 4f and 6h has been identified and discussed. Energy transfer from Ce(3+)(I) and Ce(3+)(II) to Mn(2+) ions in Y10(Si6O22N2)O2:Ce(3+),Mn(2+) samples has been validated and confirmed by the photoluminescence spectra and luminescence decay times. A color-tunable emission in Y10(Si6O22N2)O2:Ce(3+),Mn(2+) 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:Ce(3+),Mn(2+) phosphors may potentially serve as single-phase blue/reddish-orange phosphors for white-light-emitting diodes and field-emission displays.

Tunable-Color Luminescence via Energy Transfer in NaCa13/18Mg5/18PO4:A (A = Eu2+/Tb3+/Mn2+, Dy3+) Phosphors for Solid State Lighting

A series of NaCa13/18Mg5/18PO4(NCMPO):A (A = Eu(2+)/Tb(3+)/Mn(2+), Dy(3+)) phosphors have been prepared by the high-temperature solid-state reaction method. The X-ray diffraction (XRD) and Rietveld refinement, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), cathodoluminescence (CL), decay lifetimes, and PL quantum yields (QYs) were utilized to characterize the phosphors. The pure crystalline phase of as-prepared samples has been demonstrated via XRD measurement and Rietveld refinements. XPS reveals that the Eu(2+)/Tb(3+)/Mn(2+) can be efficiently doped into the crystal lattice. NCMPO:Eu(2+)/Tb(3+)/Mn(2+) phosphors can be effectively excited under UV radiation, which show tunable color from purple-blue to red including white emission based on energy transfer from Eu(2+) to Tb(3+)/Mn(2+) ions. Under low-voltage electron beam bombardment, the NCMPO:A (A = Eu(2+)/Tb(3+)/Mn(2+), Dy(3+)) display their, respectively, characteristic emissions with different colors, and the CL spectrum of NCMPO:0.04Tb(3+) has the comparable intensity to the ZnO:Zn commercial product. In addition, the calculated CIE coordinate of NCMPO:0.04Tb(3+) (0.252, 0.432) is more saturated than it (0.195, 0.417). These results reveal that NCMPO:A (A = Eu(2+)/Tb(3+)/Mn(2+), Dy(3+)) may be potential candidate phosphors for WLEDs and FEDs.