Low-voltage Cathodoluminescence Research Articles

Preparation and Luminescence Properties of YVO4:Ln and Y(V, P)O4:Ln (Ln = Eu3+, Sm3+, Dy3+) Nanofibers and Microbelts by Sol−Gel/Electrospinning Process

One-dimensional YVO4:Ln and Y(V, P)O4:Ln nanofibers and quasi-one-dimensional YVO4:Ln microbelts (Ln = Eu3+, Sm3+, Dy3+) have been prepared by a combination method of sol−gel process and electrospinning. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG−DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and time-resolved emission spectra as well as kinetic decays were used to characterize the resulting samples. Due to an efficient energy transfer from vanadate groups to dopants, YVO4:Ln phosphors showed their strong characteristic emission under ultraviolet excitation (280 nm) and low-voltage electron beam excitation (1−3 kV). The energy transfer process was further studied by the time-resolved emission spectra as well as kinetic decay curves of Eu3+ upon excitation into the VO43− ion. Furthermore, the PL emission color of YVO4:Ln nanofibers can be tuned from blue to green, orange-red, and red easily by partial replacement VO43− with PO43− and changing the doping concentrations (x) of Ln, making the materials have potential applications in fluorescent lamps and field emission displays (FEDs).

Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln=Eu3+,Ce3+,Tb3+) spherical particles

Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to D50→F71 and D50→F72 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.

Optimization of Low-Voltage Cathodoluminescence of Electron-Beam-Evaporated Y2O3:Eu Thin Film Phosphor

In this paper, we report the properties and the optimization of Y2O3:Eu cathodoluminescent thin film phosphor fabricated by electron-beam evaporation. Films were grown on quartz substrates and showed (111) orientation of cubic yttria. The Influence of film fabrication temperature regimes on the morphology and low-voltage cathodoluminescence (CL at 0.5 kV anode voltage) was studied. It was found that increase of substrate temperature from 400 to 500 °C results in larger and more regular grains with lower surface roughness. However, when substrate temperature exceeds 500 °C, the brightness of cathodoluminescence decreased owing to the deterioration of surface evenness and supposed increase of the surface recombination rate. Annealing induced grain growth and the improvement of color purity. The CL brightness at 3.5 kV anode voltage increased with annealing temperature with 0.33 eV activation energy. The CL brightness at 0.5 kV anode voltage is maximal at 800 °C annealing temperature and significantly decreases with higher annealing temperatures. CL results were analyzed with the use of threshold voltage and steepness coefficient parameters reflecting bulk and surface properties of the films respectively.

Energy Transfer and Tunable Luminescence Properties of Eu3+ in TbBO3 Microspheres via a Facile Hydrothermal Process

Tb (1- x) BO 3: xEu (3+) ( x = 0-1) microsphere phosphors have been successfully prepared by a simple hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL), low-voltage cathodoluminescence (CL), and time-resolved emission spectra as well as lifetimes were used to characterize the samples. The as-obtained phosphor samples present sphere-like agglomerates composed of nanosheets with highly crystallinity in spite of the moderate reaction temperature of 200 degrees C. Under ultraviolet excitation into the 4f (8) --> 4f (7)5d transition of Tb (3+) at 245 nm (or 284 nm) and low-voltage electron beams' excitation, TbBO 3 samples show the characteristic emission of Tb (3+) corresponding to (5)D 4 --> (7)F 6, 5, 4, 3 transitions; whereas TbBO 3:Eu (3+) samples mainly exhibit the characteristic emission of Eu (3+) corresponding to (5)D 0 --> (7)F 0, 1, 2, 3, 4 transitions due to an efficient energy transfer occurs from Tb (3+) to Eu (3+). The increase of Eu (3+) concentration leads to the increase of the energy-transfer efficiency from Tb (3+) to Eu (3+) but also enhances the probability of the interaction between neighboring Eu (3+), which results in the concentration quenching. The PL color of TbBO 3: xEu (3+) phosphors can be easily tuned from green, yellow, orange, to red-orange by changing the doping concentration ( x) of Eu (3+), making the materials have potential applications in fluorescent lamps for advertizing signs and other color display fields.

Blue-Green, Red, and White Light Emission of ZnWO4-based Phosphors for Low-Voltage Cathodoluminescence Applications

and particles were prepared by refluxing in water solution using polyethylene glycol as a capping agent and then annealed at different temperatures. The samples were characterized by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy, and cathodoluminescence spectra. The as-prepared amorphous samples annealed at high temperature are sanmartinite structure of , and the spherical morphologies are basically retained, except for the increase of the particles size (from 28 to 56 nm). The low-voltage luminescent properties of these tungstate phosphors can be tuned by the doping of ions and annealing treatment. and particles annealed at or above exhibit strong blue-green and white light emission under the excitation of low-voltage electron beams, respectively, the former originating from the intrinsic complex, and the latter due to the combination of the emissions arising from the intrinsic and doped ions. The as-prepared particles only emit a red light resulting from the (, 2, 3, 4) transitions of ions.

Nanostructured CaWO4, CaWO4:Eu3+ and CaWO4:Tb3+ Particles: Sonochemical Synthesis and Luminescent Properties

Nanostructured CaWO4, CaWO4:Eu3+, and CaWO4:Tb3+ phosphor particles were synthesized via a facile sonochemical route. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, low voltage cathodoluminescence spectra, and photoluminescence lifetimes were used to characterize the as-obtained samples. The X-ray diffraction results indicate that the samples are well crystallized with the scheelite structure of CaWO4. The transmission electron microscopy and field emission scanning electron microscopy images illustrate that the powders consist of spherical particles with sizes from 120 to 160 nm, which are the aggregates of even smaller nanoparticles ranging from 10 to 20 nm. Under UV light or electron beam excitation, the CaWO4 powder exhibited a blue emission band with a maximum at 430 nm originating from the WO4/2- groups, while the CaWO4:Eu3+ powder showed red emission dominated by 613 nm ascribed to the 5D0 --> 7F2 of Eu3+, and the CaWO4:Tb3+ powders showed emission at 544 nm, ascribed to the 5D4 --> 7F5 transition of Tb3+. The PL excitation and emission spectra suggest that the energy is transferred from WO4/2- to Eu3+ CaWO4:Eu3+ and to Tb3+ in CaWO4:Tb3+. Moreover, the energy transfer from WO4/2- to Tb3+ in CaWO4:Tb3+ is more efficient than that from WO4/2- to EU3+ in CaWO4:Eu3+. This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials.

Growth of Highly Crystalline CaMoO4:Tb3+ Phosphor Layers on Spherical SiO2 Particles via Sol−Gel Process: Structural Characterization and Luminescent Properties

Highly crystalline CaMoO4:Tb3+ phosphor layers were grown on monodisperse SiO2 particles through a simple sol-gel method, resulting in formation of core-shell structured SiO2@CaMoO4:Tb3+ submicrospheres. The resulting SiO2@CaMoO4: Tb3+ core-shell particles were fully characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and kinetic decays. The XRD results demonstrate that the CaMoO4:Tb3+ layers begin to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. SEM and TEM analysis indicates that the obtained submicrospheres have a uniform size distribution and obvious core-shell structure. SiO2@CaMoO4:Tb3+ submicrospheres show strong green emission under short ultraviolet (260 nm) and low-voltage electron beam (1-3 kV) excitation, and the emission spectra are dominated by a D-5(4) -F-7(5) transition of Tb3+(544 nm, green) from the CaMoO4:Tb3+ shells.

Low-voltage cathodoluminescence properties of Y3Al5O12:Tb3+ nanopowders

Abstract Tb 3+ -doped yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG) nanocrystallites were synthesized by modified Pechini method. The XRD patterns were taken to examine the structure and to determine the average grain size of obtained nanocrystals. The photoluminescence spectra of nanocrystalline powders were measured. The obtained powders were electrophoretically deposited on ITO-glass slides. The cathodoluminescence spectra of deposited layers were taken and compared to powders. The influence of grain size on low-voltage (≤1.5 kV) cathodoluminescence of Tb 3+ -doped Y 3 Al 5 O 12 nanocrystallites was observed. A possible application of obtained layers in field emission displays (FED) is briefly discussed.

Research on Y 2O 3:Eu Phosphor Coated with In 2O 3

Y 2O 3:Eu red phosphor for FED application was prepared by high temperature solid-state reaction. The In 2O 3 coating by precipitation method to the phosphor was applied and the analyses of XRD, Zeta potential, SEM, EDS and low voltage cathodoluminescence (CL) were conducted for investigating the coating effect. The results showed that In 2O 3 coating promoted the low voltage CL of the phosphor efficiently. The promotion was possibly due to the enhancement of the surface conductivity of the phosphor grains.

Spherical SiO2 @ GdPO4 : Eu3+ Core–Shell Phosphors: Sol–Gel Synthesis and Characterization

Nanocrystalline GdPO4 : Eu3+ phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by Pechini sol–gel method, resulting in the formation of core–shell structured SiO2 @ GdPO4 : Eu3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core–shell structured materials. Both XRD and FT-IR results indicate that GdPO4 layers have been successfully coated on the SiO2 particles, which can be further verified by the images of FESEM and TEM. Under UV light excitation, the SiO2 @ GdPO4 : Eu3+ phosphors show orange-red luminescence with Eu3+ 5D0–7F1 (593 nm) as the most prominent group. The PL excitation and emission spectra suggest that an energy transfer occurs from Gd3+ to Eu3+ in SiO2 @ GdPO4 : Eu3+ phosphors. The obtained core–shell phosphors have potential applications in FED and PDP devices.

Spherical SiO2 @ GdPO4 : Eu3+ Core–Shell Phosphors: Sol–Gel Synthesis and Characterization

Nanocrystalline GdPO4 : Eu3+ phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by Pechini sol-gel method, resulting in the formation of core-shell structured SiO2 @ GdPO4 : Eu3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core-shell structured materials. Both XRD and FT-IR results indicate that GdPO4 layers have been successfully coated on the SiO2 particles, which can be further verified by the images of FESEM and TEM. Under UV light excitation, the SiO2 @ GdPO4 : Eu3+ phosphors show orange-red luminescence with Eu3+ 5D0-7F1 (593 nm) as the most prominent group. The PL excitation and emission spectra suggest that an energy transfer occurs from Gd3+ to Eu3+ in SiO2 @ GdPO4 : Eu3+ phosphors. The obtained core-shell phosphors have potential applications in FED and PDP devices.

Sol-Gel Synthesis and Characterization of SiO2 @ NaGd ( WO4 ) 2 : Eu3 + Core-Shell-Structured Spherical Phosphor Particles

Monodisperse, core-shell-structured particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL), and low-voltage cathodoluminescence (CL) as well as time-resolved PL spectra and lifetimes. PL and CL study revealed that the core-shell-structured particles show strong red emission dominated by the transition of at with a lifetime of . The PL and CL emission intensity can be tuned by the coating number of phosphor layers on and by accelerating voltage and the filament current, respectively.

Carrier recombination near threading dislocations in GaN epilayers by low voltage cathodoluminescence

The authors present a low voltage cathodoluminescence (CL) study of as grown GaN and GaN:Si epilayers on sapphire. At 1kV they resolve individual threading dislocations on the sample surface at low temperature (5K), which appear as correlated dark spots. Analysis of CL intensity profiles across individual dislocation cores provides a direct measurement of the exciton and minority carrier diffusion lengths. Using this approach at 5K, an exciton diffusion length of 62±28nm was found for GaN:Si (∼3×1018cm−3) compared with 81±20nm for a nominally undoped n-type GaN (∼1×1016cm−3).

Carrier diffusion processes near threading dislocations in GaN and GaN:Si characterized by low voltage cathodoluminescence

Abstract We present a low temperature study of GaN epilayers by means of low voltage cathodoluminescence (CL). We show that lowering the primary electrons accelerating voltage down to 1 kV allows imaging of single threading dislocations. By using monochromatic or panchromatic low voltage CL microscopy, it is possible to extract different diffusion lengths related to free excitons, bound excitons or donor-to-acceptor pair transitions.

Silica Supported Submicron SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ Spherical Particles with a Core–Shell Structure: Sol–Gel Synthesis and Characterization

AbstractX1‐Y2SiO5:Eu3+ and X1‐Y2SiO5:Ce3+ and/or Tb3+ phosphor layers have been coated on nonaggregated, monodisperse, submicron spherical SiO2 particles by a sol–gel process, followed by surface reaction at high temperature (1000 °C), to give core/shell structured SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ particles. X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), TEM, photoluminescence (PL), low voltage cathodoluminescence (CL), and time‐resolved PL spectra and lifetimes are used to characterize these materials. The XRD results indicate that X1‐Y2SiO5 layers have been successfully coated on the surface of SiO2 particles, as further verified by the FESEM and TEM images. The PL and CL studies suggest that SiO2@Y2SiO5:Eu3+, SiO2@Y2SiO5:Tb3+ (or Ce3+/Tb3+), and SiO2@Y2SiO5:Ce3+ core/shell particles exhibit red (Eu3+, 613 nm: 5D0–7F2), green (Tb3+, 542 nm: 5D4–7F5), or blue (Ce3+, 450 nm: 5d‐4f) luminescence, respectively. PL excitation, emission, and time‐resolved spectra demonstrate that there is an energy transfer from Ce3+ to Tb3+ in the SiO2@Y2SiO5:Ce3+,Tb3+ core/shell particles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Fabrication and optical properties of core–shell structured spherical SiO 2@GdVO 4:Eu 3+ phosphors via sol–gel process

Europium-doped nanocrystalline GdVO 4 phosphor layers were coated on the surface of preformed submicron silica spheres by sol–gel method. The resulted SiO 2@Gd 0.95Eu 0.05VO 4 core–shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd 0.95Eu 0.05VO 4 layers begin to crystallize on the SiO 2 spheres after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd 0.95Eu 0.05VO 4 shells on the SiO 2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by 5D 0– 7F 2 transition of Eu 3+ (618 nm, red). The PL and CL intensities of Eu 3+ increase with increasing the annealing temperature and the number of coating cycles. The optimum concentration for Eu 3+ was determined to be 5 mol% of Gd 3+ in GdVO 4 host.

Luminescence properties of sol–gel derived spherical SiO 2@Gd 2(WO 4) 3:Eu 3+ particles with core–shell structure

Monodisperse, core–shell structured SiO 2@Gd 2(WO 4) 3:Eu 3+ particles were prepared by the sol–gel method. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL) and low-voltage cathodoluminescence (CL). PL and CL study revealed that the core–shell structured SiO 2@Gd 2(WO 4) 3:Eu 3+ particles show strong red emission dominated by the 5D 0– 7F 2 transition of Eu 3+ at 615 nm with a lifetime of 0.89 ms. The PL and CL emission intensity can be tuned by the coating number of Gd 2(WO 4) 3:Eu 3+ phosphor layers on SiO 2 particles, the size of the SiO 2 core particles, and by accelerating voltage and the filament current, respectively.

Synthesis and characterization of spherical Sr 2CeO 4 phosphors by spray pyrolysis for field emission displays

A blue emitting Sr 2CeO 4 phosphor with a one-dimensional structure has been prepared by a two-step spray pyrolysis (SP) method, starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives. The material is ultimately designed for field emission displays (FEDs). X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), field emission scanning electron microscope pictures (FE-SEM) as well as photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and lifetime measurements have been employed to characterize the samples. The morphology, PL and low voltage CL properties of Sr 2CeO 4 phosphors as-prepared using the SP method have been investigated by changing the concentration of the precursor solution, concentration of PEG, annealing temperature, acceleration voltage and filament current. The obtained Sr 2CeO 4 phosphor particles are spherical and of submicron size, 0.5–2 μm. The emission spectrum of the phosphors shows a broad band with maximum at 467 nm (lifetime=37.4 μs; CIE chromaticity coordinates: x = 0.1 5 and y = 0.2 1 ), presumably due to a ligand-to-metal charge-transfer transition.

Effect of the Thickness on Morphology and Low-Voltage Cathodoluminescence of Y2O3:Eu,Zn Thin Films

An increase in the thickness (H) of Y2O3:Eu,Zn films in the 30–500 nm range led to crystal grain growth and roughness rise, which resulted in an increase in the slope angle of the cathodoluminescence (CL) brightness vs anode voltage characteristic curve as well as in brightness at middle-level voltages. Annealing resulted in further grain growth and an increase in brightness. The dependence of threshold voltage on thickness has a minimum at 300 nm because of the effect of H on surface morphology: first, the film becomes more regular but at higher thicknesses its roughness and total surface area increase; hence, the number of surface defects and sites of radiationless recombination also increase. As a result, low-voltage CL has a maximum value at a 300 nm thickness. Thus, there is an optimum thickness for achieving maximum CL efficiency in the low electron energy region, while for higher energies efficiency increases monotonically with thickness.

P-121: Cathodoluminescent Properties of 12CaO⋅7Al[sub 2]O[sub 3]-based Phosphors

The cathodoluminescent (CL) properties of the 12CaO⋅7Al2O3-based phosphors with subnano atomic cages were investigated with a low electron accelerating voltage. We prepared Tm, Bi and Eu as activator ions and synthesized the phosphors by solid-state reaction. In the low voltage CL properties of 12CaO⋅7Al2O3: Tm, Eu phosphors, luminescence was improved over that of 12CaO⋅7Al2O3: Eu and blue chromaticity was very excellent.