Low-voltage Electron Beam Excitation Research Articles

Cationic substitution engineering induced Multi-Color light emitting of bismuth in Tantalate used for WLED

Revealing and predicting the photoluminescence behavior of trivalent bismuth activated phosphors is very important for exploiting high-quality photoluminescent materials and modulating their luminescence properties, since it commonly performs multi-type electronic transitions. In this work, the chosen matrix of Gd3TaO7, which contains only one highly symmetrical cationic crystallographic site, is favorable for analyzing luminescence behavior of Bi3+ ions, and Bi3+-activated Gd3TaO7 can emit bright green light under the near-ultraviolet (NUV) light or low voltage electron beam excitation. The cationic substitution engineering of rare earths Ln (Ln = Lu, Y and La) replacing Gd3+ ions was carried out for further regulation of spectra, and multi-color light emitting was successfully realized. However, their unusual photoluminescence properties bring a novel comprehension for the photoluminescence behavior of Bi3+ ions in this system. For well rationalizing this phenomenon, the first-principles calculation was carried out for revealing their electronic structure, combined with their geometry optimization. The results indicate multi factors have contribution in modulating the luminescence behavior of Bi3+ ions, especially the interaction between 3P1 state, metal-to-metal charge transfer state and Bi-Bi dimers. The result is favorable for us to exactly adjust the luminescence properties of Bi3+ ions.

Enhancing the blue luminescence behaviour of the Li co-doped novel phosphor ZnB2O4: Tm3+

Abstract Here we report a detailed structural analysis, and properties of the cathodoluminescence (CL), photoluminescence (PL) and 3D thermoluminescence spectra of the Tm3+ incorporated ZnB2O4 phosphor successfully synthesized through wet-chemical synthesis. The formation of a single-phase compound is verified through X-ray diffraction (XRD) studies. The phosphor shows an efficient blue emission located at 458 nm corresponding to 1D2→3F4 under both a low voltage electron beam and UV excitation. The optimal concentration of the doped Tm3+ is 0.5 mol% in CL and PL measurements. The corresponding concentration quenching mechanism is confirmed to be a multipole-multipole interaction, and the critical distance between Tm3+ ions is estimated to be 34 A. Incorporating Li+ remarkably enhances the luminescence intensity probably because of the charge compensation effect. Li ions are speculated to fill the defects in the ZnB2O4 host and then the excitation energy transfers from the host to Tm3+. Surprisingly, the thermoluminescence spectra of ZnB2O4:Tm3+ and Li+ co-doped ZnB2O4:Tm3+ recorded in the temperature range 30–400 °C follow a different pattern compared with PL and CL data. The dominant signals come from Tm3+ sites. Above room temperature, the Tm3+ ions do not show the peak temperature movement, but do exhibit a different pattern with the addition of co-doped Li+ ions. These results indicate that these phosphors are promising candidates for luminescence-based optoelectronic devices.

First-principles calculations, structure research and luminescence properties for a novel apatite blue/green phosphor Ca6Y4(SiO4)2(PO4)4O2:Eu2+/Tb3+

Abstract A novel apatite blue/green phosphor Ca6Y4(SiO4)2(PO4)4O2:Eu2+/Tb3+ (CYSP: Eu2+/Tb3+) was designed and successfully synthesized via solid-state reaction. A detailed structure analysis of CYSP was researched by Rietveld refinement and high-resolution transmission electron microscopy (HRTEM). The electronic structure of CYSP has been learned from First-principles calculation. CYSP: Eu2+ exhibits a wide reception band covering from 240 to 420 nm and performs blue emission (λmax = 445 nm). Simultaneously, CYSP: Tb3+ presents linear absorption varying from 240 to 390 nm and performs green emission (λmax = 543 nm). The temperature dependent PL properties of CYSP:Eu2+/Tb3+ was studied, which proves that the CYSP:Tb3+ has good thermal stability (over 90% under 175 °C) while the thermal stability of CYSP:Eu2+ is mediocre. The cathodoluminescence (CL) spectra of CYSP:Tb3+ below constant low-voltage electron-beam excitation were obtained and demonstrated the excellent degradation resistance properties of CYSP:Tb3+. Our results provide a novel reference in apatite-based phosphors and a novel blue-green phosphor CYSP: Tb3+ demanded to have possible applications in field emission displays.

Facile Synthesis and Down-Conversion Emission of RE3+-Doped Lutetium Oxide Nanoparticles.

Lu2O3:RE3+ (RE3+ = Eu3+, Tb3+, Ho3+) nanoparticles have been successfully synthesized by a facile homogeneous precipitation method with subsequent sintering process. The crystal structure, morphology and luminescence properties of the as-prepared samples have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), photoluminescence (PL) and cathodoluminescence (CL) spectra. Upon ultraviolet (UV) and low-voltage electron beam excitation, Lu2O3:RE3+ (RE3+ = Eu3+, Tb3+, Ho3+) nanoparticles show strong red (Eu3+,5D0 → 7F2), green (Tb3+,5D4 → 7F5), and green (Ho3+,5S2 → 5I8) emissions. They exhibit a good advantage of multicolor emissions in the visible region, and endow these kinds of materials with potential application in many fields, such as light display systems, optoelectronic devices and biological imaging.

Neutralizing the Charge Imbalance Problem in Eu3+-Activated BaAl2O4 Nanophosphors: Theoretical Insights and Experimental Validation Considering K+ Codoping.

In recent years, rare-earth-doped nanophosphors have attracted great attention in the field of luminescent materials for advanced solid-state lighting and high-resolution display applications. However, the low efficiency of concurrent red phosphors creates a major bottleneck for easy commercialization of these devices. In this work, intense red-light-emitting K+-codoped BaAl2O4:Eu3+ nanophosphors having an average crystallite size of 54 nm were synthesized via a modified sol–gel method. The derived nanophosphors exhibit strong red emission produced by the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ upon UV and low-voltage electron beam excitation. Comparative photoluminescence (PL) analysis is executed for Eu3+-activated and K+-coactivated BaAl2O4:Eu3+ nanophosphors, demonstrating remarkable enhancement in PL intensity as well as thermal stability due to K+ codoping. The origin of this PL enhancement is also analyzed from first-principles calculations using density functional theory. Achievement of charge compensation with the addition of a K+ coactivator plays an important role in increasing the radiative lifetime and color purity of the codoped nanophosphors. Obtained results substantially approve the promising prospects of this nanophosphor in the promptly growing field of solid-state lighting and field emission display devices.

Photoluminescence and cathodoluminescence studies of Er3+-activated strontium molybdate for solid-state lighting and display applications

The photoluminescence and cathodoluminescence properties of erbium ion (Er3+) activated SrMoO4 phosphor have been investigated herein. The photoluminescence (PL) emission spectra, recorded within 400–800 nm wavelength range upon 380 nm UV light excitation exhibit unusual blue emission along with its well-known green luminescence which has been explained through underlying mechanisms with the help of energy level structure. The blue luminescence of the phosphor at various Er3+-concentrations was further confirmed by computing the spectral colour coordinates that lies in the blue region of the chromaticity diagram. The cathodoluminescence (CL) spectra which were measured under low voltage electron beam excitation exhibited intense green luminescence. The PL and CL studies carried out in the synthesized phosphor indicates that it can be a useful candidate for making UV-excited light emitting diodes (LEDs) and low voltage electron beam excited field emission displays (FEDs).

Tunable emitting phosphors K3Gd(PO4)2: Tm3+-Dy3+ for light-emitting diodes and field emission displays

Spectroscopic properties of K3Gd(PO4)2: Tm3+-Dy3+ under ultraviolet (UV) light and low-voltage electron beam excitations were investigated. Upon direct excitation Tm3+ from its 6F6 level to 1D2 level, the decrease of emission intensity and lifetime of Tm3+ 1D2-3F4 emission with increasing concentration of Dy3+ in K3Gd(PO4)2: Dy3+, Tm3+ confirmed the occurrence of energy transfer from Tm3+ to Dy3+. Besides, K3Gd(PO4)2: Dy3+, Tm3+ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm3+. When 1% Tm3+ and 8% Dy3+ were codoped in the K3Gd(PO4)2, intensive white emitting light with CIE of (0.338, 0.347) was achieved upon 358 nm excitation. The cathodoluminescence spectra of K3Gd(PO4): Tm3+, Dy3+ phosphors as a function of accelerating voltage and filament current were also measured. Under low-voltage electron-beam excitation, K3Gd(PO4)2: Tm3+, Dy3+ phosphors exhibit excellent tunable emitting property. All of the above results reveal that the as-prepared K3Gd(PO4)2: Tm3+, Dy3+ phosphors have potential applications in white LEDs and FEDs.

Host-sensitized luminescence of Dy3+ in LuNbO4 under ultraviolet light and low-voltage electron beam excitation: energy transfer and white emission

A single-phase intense white-light-emission is achieved in LuNbO4:Dy3+ phosphors.

Host-Sensitized and Tunable Luminescence of GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) Nanocrystalline Phosphors with Abundant Color.

Up to now, GdNbO4 has always been regarded as an essentially inert material in the visible region with excitation of UV light and electron beams. Nevertheless, here we demonstrate a new recreating blue emission of GdNbO4 nanocrystalline phosphors with a quantum efficiency of 41.6% and host sensitized luminescence in GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) nanocrystalline phosphors with abundant color in response to UV light and electron beams. The GdNbO4 and GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) nanocrystalline phosphors were synthesized by a Pechini-type sol-gel process. With excitation of UV light and low-voltage electron beams, the obtained GdNbO4 nanocrystalline phosphor presents a strong blue luminescence from 280 to 650 nm centered around 440 nm, and the GdNbO4:Ln3+ nanocrystalline phosphors show both host emission and respective emission lines derived from the characterize f-f transitions of the doping Eu3+, Tb3+, and Tm3+ ions. The luminescence color of GdNbO4:Ln3+ nanocrystalline phosphors can be tuned from blue to green, red, blue-green, orange, pinkish, white, etc. by varying the doping species, concentration, and relative ratio of the codoping rare earth ions in GdNbO4 host lattice. A single-phase white-light-emission has been realized in Eu3+/Tb3+/Tm3+ triply doped GdNbO4 nanocrystalline phosphors. The luminescence properties and mechanisms of GdNbO4 and GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) are updated.

Upconversion- and cathodo-luminescence properties of Yb3+/Ho3+/Li+ tridoped Lu6O5F8 nanoparticles

Yb3+/Ho3+/Li+ tridoped Lu6O5F8 as a novel phosphor was prepared by a coprecipitation method. It is found that Li+ doping could enhance the emission intensity of Yb3+/Ho3+ codoped Lu6O5F8 both under the excitation at 980nm and low-voltage electron beam. Under 980nm laser excitation, the intensity of red emission is slightly stronger than that of green emission, generating an overall yellow output in Lu6O5F8:20%Yb3+,1%Ho3+,x%Li+ (0≤x≤8) nanoparticles, and the reason for this phenomenon is discussed in detail. Meanwhile, under low-voltage electron beam excitation, spectral results demonstrated that the intensity of red emission is much stronger than that of green emission, yielding a red color output. Therefore, Lu6O5F8:20%Yb3+,1%Ho3+,x%Li+ (0≤x≤8) nanoparticles have potential applications in luminescent display panels and field emission displays.

Local Field Enhancement-Induced Enriched Cathodoluminescence Behavior from CuI-RGO Nanophosphor Composite for Field-Emission Display Applications.

Field-emission displays (FEDs) constitute one of the major foci of the cutting edge materials research because of the increasingly escalating demand for high-resolution display panels. However, poor efficiencies of the concurrent low voltage cathodoluminescence (CL) phosphors have created a serious bottleneck in the commercialization of such devices. Herein we report a novel CuI-RGO composite nanophosphor that exhibits bright red emission under low voltage electron beam excitation. Quantitative assessment of CL spectra reveals that CuI-RGO nanocomposite phosphor leads to the 4-fold enhancement in the CL intensity as compared to the pristine CuI counterpart. Addition of RGO in the CuI matrix facilitates efficient triggering of luminescence centers that are activated by local electric field enhancement at the CuI-RGO contact points. In addition, conducting RGO also reduces the negative loading problem on the surface of the nanophosphor composite. The concept presented here opens up a novel generic route for enhancing CL intensity of the existing (nano)phosphors as well as validates the bright prospects of the CuI-RGO composite nanophosphor in this rapidly growing field.

Synthesis and luminescent properties of red-emitting Eu3+-activated Ca0.5Sr0.5MoO4 phosphors

Eu3+-activated Ca0.5Sr0.5MoO4 phosphors were prepared by a high-temperature solid-state reaction method. The X-ray diffraction patterns revealed that the obtained samples had a pure tetragonal phase. Under 393 nm excitation, all the samples exhibited the characteristic emissions of Eu3+ ions and the photoluminescence (PL) emission intensities showed an upward trend with elevating the Eu3+ ion concentration, while the concentration quenching effect took place when the Eu3+ ion concentration was over 9 mol% and the critical distance was determined to be about 13.09 A. Furthermore, the cathodoluminescence (CL) spectra, which were measured under low-voltage electron-beam excitation, demonstrated that the Ca0.41Sr0.5MoO4:0.09Eu3+ phosphor had excellent CL performance. Also, the alkali metal ions, such as Li+, Na+, and K+, were used as the charge compensator to modify the PL emission intensity of the Ca0.41Sr0.5MoO4:0.09Eu3+ phosphor and the phosphor compensated by Na+ ions showed the strongest PL emission intensity.

Morphology-controlled hydrothermal synthesis and multifunctional luminescence properties of micro-crystals Gd6O5F8:Eu3+/Tb3+/Tm3+

This paper reports on a facile hydrothermal route that has been developed to synthesize a precursor Gd(OH)2.14F0.86 and a novel phosphor host Gd6O5F8. The morphology of the micro-sized Gd(OH)2.14F0.86/Gd6O5F8 can be easily tuned in a controlled manner by altering the fluorine sources, alkali solutions, reaction time and the pH values of the initial solution. Under ultraviolet (UV) light, vacuum ultraviolet (VUV) light and low-voltage electron beam excitation, the Gd(OH)2.14F0.86/Gd6O5F8:Ln3+ (Eu, Tb and Tm) samples show the characteristic f–f transitions of the Ln3+ ions and give bright red, green and blue emissions, respectively. The results prove that the as-synthesized Gd6O5F8 are excellent host lattices for rare earth luminescence, which may find potential applications in solid-state light, field emission displays (FEDs).

Pechini-type sol–gel synthesis and multicolor-tunable emission properties of GdY(MoO4)3:RE3+ (RE = Eu, Dy, Sm, Tb) phosphors

GdY(MoO4)3:RE3+ (RE=Eu, Dy, Sm, Tb) phosphor were synthesized via a Pechini-type sol–gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) and cathodoluminescence (CL) spectra, and decay lifetimes etc were utilized to characterize the resulting samples. After annealed at 800°C for 4h in air, pure GdY(MoO4)3 phase can form. When the calcination temperature is further increased to 1100°C, the crystallinity and luminescence intensity reach the best in our experiments. Under UV light and low-voltage electron beam excitation, the GdY(MoO4)3:Eu3+, GdY(MoO4)3:Dy3+, GdY(MoO4)3:Sm3+ and GdY(MoO4)3:Tb3+ phosphors exhibit the characteristic emission of Eu3+ (5D0-7F2, red), Dy3+ (4F9/2–6H13/2, yellow), Sm3+ (4G5/2–6H7/2, orange) and Tb3+ (5D4–7F5, green) with a high color purity, respectively. The Eu3+ and Tb3+ co-doping phosphors are capable of showing color-tunable emissions in the visible region under single-wavelength excitation. The luminescence mechanism and concentration quenching effect were discussed in detail.

VUV–vis photoluminescence, low-voltage cathodoluminescence and electron-vibrational interaction of Mn2+ in Ba2MgSi2O7

A series of Mn2+ doped Ba2MgSi2O7 phosphors with a nominal formula Ba2Mg1−xMnxSi2O7 (x=0.01–0.13) were prepared by a high-temperature solid-state reaction technique. Their VUV–vis photoluminescence spectra, fluorescence decay curves, and low-voltage cathodoluminescence spectra were measured and discussed in detail. The results confirm that the Mn2+ ions enter into the four-coordinated Mg2+ site in Ba2MgSi2O7 host lattice. The main electron-vibrational interaction (EVI) parameters (such as Huang–Rhys factor, effective phonon energy and position of the zero-phonon line) were evaluated from the experimental spectra. Furthermore, the concentration and the temperature dependence of the emission intensity and the luminescence decays of Ba2MgSi2O7:Mn2+ were investigated, accordingly the schematic energy levels for Mn2+ in Ba2MgSi2O7 were proposed. Due to the high emission intensity under low-voltage electron beam excitation, a further optimized sample Ba2Mg0.95Mn0.05Si2O7 can be considered as a promising green phosphor for field emission displays (FEDs).

Photoluminescence and cathodoluminescence properties of Na2MgGeO4:Mn2+ green phosphors

The cathodoluminescence properties of green phosphor Na2MgGeO4:0.03Mn2+.

Facile Template Free Synthesis and Tunable RGB Luminescent Properties of Ln3+-Doped Yttrium Oxide Nanospheres

Well-dispersed and uniform Y2O3:Ln3+ (Ln3+ = Eu3+/Tb3+/Yb3+/Er3+/Tm3+) nanospheres have been successfully prepared at 180°C via a facile hydrothermal route without any template, followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra as well as kinetic decay were employed to characterize the samples. It was found that the hydrothermal precursor could act as a template to obtain the corresponding oxide Y2O3 which inherited the original morphology of the hydrothermal precursor. The TEM and SEM images indicate that the samples consist of separated spheres with a mean diameter of about 260 nm. Under the excitation of ultraviolet (UV) light, 980-nm laser, and low-voltage electron beams, the Y2O3:Ln3+ phosphors all exhibited bright red, green and blue emissions, respectively, which were easily observed by naked eyes. The corresponding luminescent mechanism had been discussed. Due to the excellent PL (including up-conversion and down-conversion) and CL properties, multicolor tunable luminescence, ideal spherical shape, and cheap Y2O3 host, the as-prepared phosphors can potentially be used as fluorescent lamps, up-conversion fluorescent labels, and field emission display devices.

CaGdAlO4:Tb3+/Eu3+as promising phosphors for full-color field emission displays

Eu3+ and/or Tb3+-doped CaGdAlO4 phosphor samples were synthesized via a conventional high temperature solid-state reaction process. X-Ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) as well as cathodoluminescence (CL) spectra were used to characterize the samples. For CaGdAlO4:Tb3+, the concentration of doped Tb3+ has a significant effect on the 5D3/5D4 emission intensity due to the dipole–dipole cross-relaxation mechanism from 5D3 to 5D4. Under the 4f8 → 4f75d excitation of Tb3+ or low-voltage electron beam excitation, the CaGdAlO4:Tb3+ samples show tunable luminescence from blue to cyan and then to green with the variation of the Tb3+-doping concentration. For CaGdAlO4:Eu3+, the samples exhibit a reddish-orange emission corresponding to the 5D0,1 → 7F0,1,2,3 transitions of Eu3+. Energy transfer can take place from Tb3+ to Eu3+ when they are codoped in one host. Furthermore, for CaGdAlO4:Tb3+/Eu3+, a white emission can be realized in the single phase CaGdAlO4 host by reasonably adjusting the doping concentrations of Tb3+ and Eu3+ under low-voltage electron beam excitation. Due to the excellent PL, CL properties and good CIE chromaticity coordinates, the as-prepared Tb3+/Eu3+-doped CaGdAlO4 nanocrystalline phosphors have potential applications in field emission display devices.

Well-Defined LaBO<sub>3</sub>:Tb<sup>3+</sup> Hierarchical Architectures: Facile Synthesis and Luminescence Properties

Well-defined LaBO3 hierarchical architectures have been successfully synthesized by a designed hydrothermal conversion method. La (OH)3 nanowires were prepared through a simple hydrothermal process. Subsequently, uniform 3D LaBO3 architectures were synthesized at the expense of the La (OH)3 nanowires during a hydrothermal process. The whole process was carried out under aqueous conditions without the use of any organic solvent, surfactant, or catalyst. The as-obtained LaBO3:Tb3+ product shows strong characteristic green emission under ultraviolet or low-voltage electron beam excitation, which might find potential applications in fields of fluorescent lamps, display systems, and optoelectronic devices.

Synthesis and luminescence characteristics of nitride Ca1.4Al2.8Si9.2N16:Ce3+, Li+for light-emitting devices and field emission displays

A green-emitting nitride phosphor Ca1.4Al2.8Si9.2N16:Ce3+, Li+ (CASN:Ce) has been successfully synthesized which is applicable to near-ultraviolet based light-emitting diodes (LEDs) and field emission displays (FEDs). The characteristic photoluminescence (PL) properties were studied in detail by PL excitation, emission spectra and time-resolved spectroscopy. CASN:0.10Ce exhibits broad-band green emission centered at ∼525 nm (FWHM ≈ 135 nm) under 395 nm excitation and with excellent thermal stability. The effect of host lattice composition on PL properties was also discussed. The cathodoluminescence (CL) spectra as a function of accelerating voltage and probe current were also studied. Excellent degradation resistance properties with good color stability were obtained by continuous low-voltage electron-beam excitation of the phosphor.