Luminescence properties of Mn doped Zn2SiO4 phosphor films synthesized by combustion CVD

Zn₂SiO₄:Mn²⁺ phosphor films were successfully prepared by a novel combustion chemical vapor deposition (CCVD) method. In the CCVD process, a flammable solution, containing precursor materials, is atomized and sprayed through a specially designed nozzle and ignited to form a combustion flame. This enables crystallized films to be directly deposited onto a substrate in open-atmosphere with no post deposition heat treatment. SEM images indicated that the film deposited at 1200 °C consisted of densely packed particles with a fine grain size of several 100 nm. Strong Photoluminescence (PL) and cathodoluminescence (CL) intensities were observed with Zn₂SiO₄:Mn²⁺ samples deposited at a substrate temperature of 1200 °C exhibiting the best crystallinity and highest luminescence. The optimum doping level for films deposited using CCVD was found to be ∼4 mol% Mn²⁺ of starting concentration, with a maximum CL luminescence equivalent to 53% of the luminescence measured from a commercial powder phosphor. A relatively fast CL decay with life time about 0.6-0.7 ms was also observed from these films.     

Y2SiO5:Tb phosphor particles prepared from colloidal and aqueous solutions by spray pyrolysis

Green-emitting Y₂SiO₅:Tb phosphor particles with fine size, spherical shape, filled morphology, high crystallinity, and good brightness were synthesized by a spray pyrolysis process. The effect of silicon precursor type on the morphology, crystal structure, crystallinity, and photoluminescence efficiency of Y₂SiO₅:Tb phosphor particles was investigated. The particles prepared from an artificial colloidal solution obtained by dispersing fumed silica particles had a pure monoclinic X2 crystalline phase, which is more appropriate for application to displays, after post-treatment at 1300 °C. On the other hand, the particles prepared from 100% tetraethyl orthosilicate (TEOS) reagent had an X2 phase and small amounts of X1 and impurity phases such as Y₂Si₂O₇ and Y_4.67Si₃O₁₃ due to the phase-segregation characteristics of the TEOS precursor. The photoluminescence characteristics of Y₂SiO₅:Tb phosphor particles were strongly affected by the silicon source used. The photoluminescence intensities increased with the fumed silica/TEOS ratio. The particles prepared from 100% fumed silica showed the maximum photoluminescence intensity, which is 22% higher than that of particles prepared from 100% TEOS. PACS 81.20.Rg; 78.55.Hx; 78.40.Ha; 81.05.Hd; 81.40.Tv     

The synthesis of (Y<Subscript>1-x</Subscript>Gd<Subscript>x</Subscript>)<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu phosphor particles by flame spray pyrolysis with LiCl flux

(Y_1-xGd_x)₂O₃:Eu phosphor particles with dense morphology were prepared by flame spray pyrolysis and the effect of LiCl flux on the crystallinity, morphology, and photoluminescence characteristics of the particles was investigated. All as-prepared particles had monoclinic phase regardless of flux and had different luminescence characteristics from those of commercial Y₂O₃:Eu particles of cubic phase. The addition of LiCl flux reduced the post-treatment temperature by 300 °C for phase transformation from the monoclinic phase to the cubic phase. The post-treatment temperature of (Y_0.75Gd_0.25)₂O₃:Eu particles for phase transformation decreased from 1100 °C to 700 °C when LiCl flux was used. The morphology of the particles was also influenced by the Y/Gd ratio and the LiCl flux. The as-prepared particles had spherical shape and non-aggregation characteristics regardless of Y/Gd ratio and flux. The sphericity of the as-prepared particles prepared without flux was maintained after post-treatment for phase transformation in all Y/Gd ratios. However, LiCl addition promoted the aggregation between product particles. The prepared particles had high photoluminescence intensities comparable to that of the commercial product. PACS 64.70.Kb; 78.55.-m; 81.20.Rg; 75.50.Tt     

One-step synthesis of the green phosphor Ce-Tb-Mg-Al-O system with spherical particle shape and fine size

Spray pyrolysis method was applied to the preparation of Ce_0.6Tb_0.4MgAl₁₁O₁₉ green phosphor particles. The characteristics of as-prepared particles such as photoluminescence, crystallinity, and morphology were compared with those of post-treated particles. The as-prepared particles at 1700 °C had higher crystallinity and photoluminescence properties compared with those of post-treated particles. The morphology of as-prepared particles obtained at low temperatures changed from spherical shape to plate-like shape after post-treatment at 1400 °C for 3 h. The particles directly prepared at 1700 °C had the mean size of 0.7 μm and non-aggregation characteristics. This study has demonstrated that without post-treatment processing/annealing, spherical phosphor particles having complex composition could be prepared by a one-step synthesis. Received: 20 December 1999 / Accepted: 25 May 2000 / Published online: 9 August 2000     

Synthesis and characterization of Mn-doped Zn2SiO4/SiO2 phosphor particles in core-shell structure

Manganese-doped zinc silicate (Zn₂SiO₄:Mn) is a kind of phosphor material that has a photo-luminescent (PL) and cathode-luminescent (CL) properties with intensive green light emission at 520 nm. The particles consisting of SiO₂@Zn₂SiO₄:Mn (SiO₂ core-Zn₂SiO₄:Mn shell) were synthesized via colloidal process and forced precipitation. After drying, the Zn/Mn precipitates were coated on the surface of SiO₂ particles. The Zn/Mn precipitates reacted with SiO₂ and transformed to Zn₂SiO₄:Mn by suitable calcination. The microstructure, crystalline phase, and luminescent characteristics of the products were studied. Besides, a CL device consisting of the core-shell powder was characterized.     

Size-dependent photoluminescence properties under vacuum ultraviolet excitation of Zn2SiO4:Mn nanophosphors

The Zn₂SiO₄:Mn²⁺ nanophosphors with different particle sizes were synthesized via the hydrothermal method by adjusting the concentrations of surfactant and the hydrothermal temperature. The behavior of the photoluminescence as a function of phosphor particle sizes under vacuum ultraviolet excitation was investigated. Higher critical quenching concentration with decreasing particle size of the Zn₂SiO₄:Mn²⁺ nanophosphors was observed. This is ascribed to the hindrance of energy transfer between luminescence centers under vacuum ultraviolet excitation. The prolonged decay time in smaller samples provides further evidence that the energy transfer confinement has an effect on the photoluminescence properties.     

Controlled synthesis and relationship between luminescent properties and shape/crystal structure of Zn2SiO4:MN phosphor

Mn-doped Zn₂SiO₄ phosphors with different morphology and crystal structure, which show different luminescence and photoluminescence intensity, were synthesized via a low-temperature hydrothermal route without further calcining treatment. As-synthesized zinc silicate nanostructures show green or yellow luminescence depending on their different crystal structure obtained under different preparation conditions. The yellow peak occurring at 575 nm comes from the β-phase zinc silicate, while the green peak centering at 525 nm results from the usual α-phase zinc silicate. From photoluminescence spectra, it is found that Zn₂SiO₄ nanorods have higher photoluminescence intensity than Zn₂SiO₄ nanoparticles. It can be ascribed to reduced surface-damaged region and high crystallinity of nanorods.     

High luminance of new green emitting phosphor, Mg2SnO4:Mn

Mg₂SnO₄, which has an inverse spinel structure, was adopted as the host material of a new green emitting phosphor. Luminescence properties of the manganese-doped magnesium tin oxide prepared by the solid state reaction were investigated under vacuum ultraviolet (VUV) ray and low-voltage electron excitation. The Mg₂SnO₄:Mn phosphor exhibited green luminescence with the emission spectrum centered at 500 nm due to spin flip transition of the d-orbital electron associated with the Mn²⁺ ion. Optimum Mn concentration of Mg₂SnO₄:Mn under VUV excitation with 147 nm wavelength and electron beam excitation with 800 V excitation voltage are 0.25 and 0.6 mol%, respectively. The emission intensities of Mg₂SnO₄:Mn phosphors under the two excitation sources are higher than those of Zn₂SiO₄:Mn and ZnGa₂O₄:Mn phosphors. At 0.25 mol% of Mn concentration, on the other hand, the decay time is shorter than 10 ms.     

Photoluminescence of the nanosized xerogel Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript> in pores of anodic alumina

The photoluminescence properties of a composite material prepared by the introduction of the nanosized phosphor Zn₂SiO₄:Mn²⁺ into porous anodic alumina have been investigated. Scanning electron microscopy studies have revealed that Zn₂SiO₄:Mn²⁺ particles are uniformly distributed in 70% of the volume of the pore channels. The samples exhibit an intense luminescence in the range of 2.3–3.0 eV, which corresponds to the emission of different types of F centers in alumina. After the formation of Zn₂SiO₄:Mn²⁺ nanoparticles in the pores, an intense photoluminescence band is observed at 2.4 eV due to the ⁴T₁–⁶A₁ electronic transition within the 3d shell of the Mn²⁺ activator ion. It has been found that the maximum of the photoluminescence of Zn₂SiO₄:Mn²⁺ xerogel nanoparticles located in the porous matrix is shifted to higher energies, and the luminescence decay time decreases significantly.     

Highly efficient transparent Zn2SiO4:Mn phosphor film on quartz glass

Highly efficient transparent Zn₂SiO₄:Mn²⁺ film phosphors on quartz substrates were deposited by the thermal diffusion of sputtered ZnO:Mn film. They show a textured structure with some preferred orientations. Our film phosphor shows, for the best photoluminescence (PL) brightness, a green PL brightness of about 20% of a commercial Zn₂SiO₄:Mn²⁺ powder phosphor screen. The film shows a high transmittance of more than 10% at the red-color region. The excellence in PL brightness and transmittance can be explained in terms of the textured crystal growth with a continuous gradient of Zn₂SiO₄: Mn²⁺ crystals.     

Fine structure in the low temperature luminescence of Zn2SiO4:Mn and Mg4Ta2O9:Mn

The luminescence of powder samples of the well-known green-emitting Zn₂SiO₄:Mn and the red-emitting Mg₄Ta₂O₉:Mn phosphor shows a considerable fine structure at 4° K in appropriately prepared samples containing a sufficiently low Mn concentration. For (Zn_1-xMn_x)₂SiO₄ (0.0005?x?0.05) two sharp lines were found which are interpreted as due to zero phonon transitions between the ⁴T₁ and ⁶A₁ levels of Mn²⁺ ions on the two crystallographically different zinc sites. The remaining structure is ascribed to vibronic sidebands. The decay times of the luminescence bands associated with the two sites differ; they are 12 and 15 ms for the high and low energy bands respectively. The experimental results of Vlam are confirmed by our data. In addition some (Zn_1-yBe_y)₂SiO₄:Mn (0.025? y ?1) samples were investigated. In Mg₄Ta₂O₉:Mn two zero phonon lines could be identified, indicating that in this material Mn²⁺ is distributed over two inequivalent Mg sites. Most of the phonon replicas were found at intervals of 15 meV. Raman scattering experiments showed that this energy corresponds to one of the lattice vibrations. The decay time of this luminescence band is 1.0 ms.     

Evaluating Zn2SiO4:Mn phosphor for use in medical imaging radiation detectors

2 SiO₄:Mn phosphor was evaluated for use in radiation detectors of medical imaging systems. Zn₂SiO₄:Mn was used in the form of laboratory-prepared fluorescent layers (screens) with coating weights from 18 to 150 mg/cm². The phosphor was excited to luminescence by low-energy X-raysusing X-raytube voltages ranging from 15 to 50 kVp. The number of emitted optical photons per incident X-rayquantum was thus determined for various X-rayenergies and phosphor coating weights. The optical emission spectrum was also measured and it was used to evaluate the spectral compatibility of Zn₂SiO₄:Mn with radiographic films, photocathodes and the Si photodiode. Finally, phosphor optical properties were estimated by fitting a theoretical model to experimental data. Results showed that Zn₂SiO₄:Mn is more efficient for low-energy X-rays. Its intrinsic conversion efficiency was found equal to 0.08, which is comparable to that of actually used phosphors. Zn₂SiO₄:Mn was also adequately compatible with orthochromatic films and the ES-20 photocathode, thus being appropriate for low-voltage radiography and fluoroscopy. Received: 31 July 1998/Accepted: 3 August 1998     

Enhanced photoluminescence properties of Zn2SiO4:Mn co-activated with Y/Li under VUV excitation

A series of green phosphors Zn_1.92−2xY_xLi_xSiO₄:0.08Mn²⁺ (0≤x≤0.03) were prepared by solid-state synthesis method. Phase and lattice parameters of the synthesized phosphors were characterized by powder X-ray diffractometer (XRD) and the co-doped effects of Y³⁺/Li⁺ upon emission intensity and decay time were investigated under 147 nm excitation. The results indicate that the co-doping of Y³⁺/Li⁺ has favorable influence on the photoluminescence properties of Zn₂SiO₄:Mn²⁺, and the optimal photoluminescence intensity of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 103% of that of commercial phosphor when the doping concentration of Y³⁺/Li⁺ is 0.01 mol. Additionally, the decay time of phosphor is much shortened and the decay time of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 3.39 ms, shorter by 1.83 ms than that of commercial product after Y³⁺/Li⁺ co-doping.     

Low-temperature synthesis of Zn2SiO4:Mn green photoluminescence phosphor

Zn₂SiO₄:Mn green phosphor having comparable photoluminescence (PL) efficiency with commercial phosphor has been synthesized at 1000 °C using solid state reactions involving ZnO, silicic acid and manganese acetate. The water of crystallization attached to SiO₂ in silicic acid whose dissociation at 1000 °C seem to promote the sintering efficiency of Zn₂SiO₄:Mn. Incremental ZnO addition and re-firing at 1000 °C promote the diffusion rate of ZnO and SiO₂. The formation of a single crystalline phase of willemite structure in the samples was confirmed by powder XRD measurements. The phosphor exhibit an intense excitation band centered around 275 nm and a relatively weak excitation centered around 380 nm while the broad band green emission peaks at 524 nm. Other parameters studied include PL spectra, grain morphology, ZnO/SiO₂ molar ratio, Mn concentration, co-dopant/flux and the effect of chemical forms of Mn dopant as well as silica on the PL efficiency.     

Effect of the geometric shape of Lu 2 O 3 : Eu spherical nanocrystals on their spontaneous luminescence

Monodisperse red phosphor particles 100 nm in diameter with the Lu_1.90Eu_0.10O₃ composition have been prepared using the developed technique for synthesizing spherical colloidal lutetium oxide particles with a size dispersion in the range 10–15%. The structure of spherical nanoparticles has been investigated, their excitation and photoluminescence spectra have been analyzed, and the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions has been considered. It has been found that the luminescence decay time for spherical particles increases by a factor of 1.39 compared to that for a powdered phosphor Lu₂O₃: Eu (5 at %) prepared and treated under the same temperature conditions as the Lu₂O₃: Eu (5 at %) spherical particles. This effect has been associated with the change in the photonic local density of states in spherical optical cavities consisting of particles of the phosphor.     

Luminescence properties of green emission of SiO2/Zn2SiO4:Mn nanocomposite prepared by sol–gel method

Green light emitting Mn²⁺ doped Zn₂SiO₄ particles embedded in SiO₂ host matrix were synthesized by a sol–gel method. After the incorporation of ZnO:Mn nanoparticles in a silica monolith using sol–gel method with supercritical drying of ethyl alcohol in two steps, it was heat treated in air at 1200 °C for 2 h in order to obtain the SiO₂/α-Zn₂SiO₄:Mn nanocomposites. The microstructure of phosphor crystals was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD results indicate that the pure phase α-Zn₂SiO₄ with rhombohedral structure was obtained after thermal treatment at 1200 °C. The SiO₂/α-Zn₂SiO₄:Mn nanocomposites with a Mn doping concentration of 1.5 at% exhibit two broadband emissions in the visible range: a strong green emission at around 525 nm and a second one in the range between 560 and 608 nm. This nanocomposite with a Mn doping concentration of 0.05 shows the highest relative emission intensity. Upon 255 nm excitation, the luminescence decay time of the green emission of Zn₂SiO₄:Mn around 525 nm is 11 ms. The luminescence spectra at 525 nm (⁴T₁–⁶A₁) and lifetime of the excited state of Mn²⁺ ions-doped Zn₂SiO₄ nanocrystals are investigated.     

Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization

Spherical SiO₂ particles have been coated with Zn₂SiO₄:Eu³⁺ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn₂SiO₄:Eu³⁺@SiO₂ particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn₂SiO₄:Eu³⁺@SiO₂ particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu³⁺ concentration, annealing temperature and charge compensators of Li⁺ ions on the PL emission intensities were investigated in detail.     

Luminescence properties and mechanism of Zn1.92−xBaxSi1−yTiyO4:0.08Mn phosphors in VUV region

The present commercial phosphor Zn₂SiO₄:Mn²⁺ requires further improvement because of its long decay time. In this work, the co-doping effects of Ba²⁺ and Ti⁴⁺ upon emission intensity and decay time were investigated. Ba²⁺ and Ti⁴⁺ cations have favorable influences on the photoluminescent properties. When doped with appropriate amount of Ba²⁺, the intensity of green emission was increased 12% and the decay time was shortened 18%. When doped with appropriate amount of Ti⁴⁺, the luminescence intensity was enhanced a little, and the decay time was shortened 14%. Ba²⁺ and Ti⁴⁺ were co-doped in Zn₂SiO₄:Mn²⁺ system, the luminescence intensity was enhanced 18%, and the decay time was shortened sharply (about 31%).     

Effects of dopant concentrations and firing temperatures on decay kinetics of manganese doped willemite nanopowders

Nanocrystallline willemite, Zn_2−xMn_xSiO₄ (0.5≤x≤5 mol%), doped with variable concentration of divalent manganese ions, phosphor powders were prepared using the simple wet-chemical sol-gel method combined with furnace firing at 800, 900, and 1000 °C. X-ray diffraction (XRD) and high resolution X-ray photoelectron (HR-XPS) scans confirm the presence of willemite phase of Zn₂SiO₄. Laser-induced phosphorescence decay measurements of Zn_2−xMn_xSiO₄ nanophosphors were investigated using high peak power pulsed UV nitrogen laser (λ=337.1 nm). The decay curves show non-single exponential behavior with long term decay rate. Various parameters describing the strength of optical transitions in atoms and molecules such as, Einstein's A and B coefficients, ‘f’, integrated cross-section, and transition dipole moment values have been calculated. The long term decay rate of optical transition parameters was found to be somewhat temperature and concentration dependent.     

Prepare high efficiency Mn-doped Zn2SiO4 green phosphors in air using nano-particles

In this study, nano-scale precursors of ZnO, SiO₂, and MnO₂ powders were used to prepare mixtures with the compositions of 2ZnO+SiO₂+X mol% MnO₂ (X=MnO₂/2ZnO, abbreviated as Zn₂SiO₄-X-MnO₂), where 2≤X≤5. The mixed Zn₂SiO₄-X-MnO₂ mixtures were calcined from 900 to 1300 °C in air in order to synthesize Zn₂SiO₄:Mn²⁺ green phosphors. The X-ray diffraction patterns of Zn₂SiO₄-X-MnO₂ particles indicated that ZnO was present in the 900 °C-calcined Zn₂SiO₄-X-MnO₂ phosphors, but not in particles calcined at temperatures of 1000 °C and higher. However, the unapparent secondary phase of ZnMnO₃ was found in the 1200 and 1300 °C-calcined Zn₂SiO₄-5-MnO₂ compositions. The luminescent characteristics of Zn₂SiO₄-X-Mn²⁺ phosphors were compared with that of a commercial product (Nichia Corp., Japan). The photoluminescence (PL) intensity of 1200 °C-calcined Zn₂SiO₄-4-MnO₂ phosphors was higher and the decay times of all synthesized Zn₂SiO₄-X-MnO₂ phosphors were longer than those of the commercial product.