YAG:Ce nano-sized phosphor particles prepared by a solvothermal method

Nano-sized Ce-doped YAG phosphor particles were synthesized by a mixed solvothermal method using the stoichiometric amounts of inorganic aluminum and yttrium salts. The formation of YAG:Ce was investigated by means of XRD and TG-DTA. The purified YAG crystalline phases was obtained under moderate synthesis condition (300 °C and 10 MPa), this indicated that ethanol replaced part of water as solvent favoring the formation of YAG. TEM images showed that YAG:Ce phosphor particles were basically spherical in shape, well dispersed and a mean grain size about 60 nm. The particle absorbed excitation energy in the range 403-510 nm, and the maximum excitation wavelength was near 470 nm. The crystalline YAG:Ce showed broad emission peaks in the range 480-650 nm and had maximum intensity at 528 nm. The excitation and emission intensity increased with increasing the synthesis temperature from 280 to 300 °C, and get the maximum brightness at 300 °C.     

Low temperature synthesis of SrS:Ce phosphor by carbothermal reduction method: Influence of sulfur and charge compensator on the luminescent properties

We report here on an ecologically friendly carbothermal reduction method to realize SrS:Ce phosphor. The method effectively reduces the preparation temperature by 100 °C. The effect of sulfur and charge compensator were studied separately and in combination, on the luminescent properties of SrS:Ce phosphor prepared from SrSO₄:Ce(SO₄)₂·4H₂O using this method without inert gas or hazardous gas (H₂S) environment. To analyze the role of charge compensator on the luminescent emission property of SrS:Ce, various fluxes, viz., NH₄Cl, NaCl were used. The synthesized products were characterized by XRD, photoluminescence emission and excitation spectroscopy (PLE). SrS:Ce showed a bright blue-green emission at 480 and 540 nm corresponding to energy bands originating from ²T_2g (5d) to ²F_7/2, ²F_5/2 (4f) of Ce³⁺ transitions. The characterization results showed the formation of SrS calcined at 900 °C for 5 h with an increase in blue-green luminescence intensity after the addition of sulfur and charge compensator, separately. When the sulfur and NH₄Cl were jointly added, the intensity of blue emission was enhanced, whereas, that of green emission was suppressed. The excitation spectrum showed a fundamental absorption of SrS host crystal lattice at 283 nm and Ce³⁺ absorption at 430 nm respectively. The CIE (Commission International de’Eclairge) chromaticity coordinates of the phosphor are also reported.     

A promising red phosphor MgMoO4:Eu for white light emitting diodes

Motivated by the need for new red phosphors for solid-state lighting applications Eu³⁺-doped MgMoO₄ was prepared by solid-state reaction and its excitation and emission spectra were measured at room temperature. In addition, the effects of firing temperature and Eu³⁺ doping concentration on the PL intensities were also investigated. Compared with Y₂O₂S:0.05Eu³⁺, the obtained Mg_0.80MoO₄:Eu³⁺_0.20 phosphor shows a stronger excitation band near 400 nm and intensely red-emission lines at 616 nm correspond to the forced electric dipole ⁵D₀ → ⁷F₂ transitions on Eu³⁺ under 394 nm light excitation. The CIE chromaticity coordinates (x = 0.651, y = 0.348) of Mg_0.80MoO₄:Eu³⁺_0.20 close to the NTSC (National Television Standard Committee) standard values, and therefore may find application on near UV InGaN chip-based white light emitting diodes.     

Continuous production of phosphor YAG:Tb nanoparticles by hydrothermal synthesis in supercritical water

Phosphor YAG:Tb ((Y_2.7Tb_0.3)Al₅O₁₂) nano particles were synthesized by a hydrothermal method at supercritical conditions (400 °C and 30 MPa) using a flow reactor. Hydroxide sol solutions formed by stoichiometric aluminum nitrate, yttrium nitrate, terbium nitrate and potassium hydroxide solutions. The relationship between particle size and experimental variables including pH, concentration of coexistent ions and hydroxide sol were investigated. Particles were characterized by XRD, TEM and photo-luminescence measurements. Particle size of YAG:Tb became finer as pH was increased or potassium nitrate concentration of the starting metal salt solution was increased. By removing the coexisting ions (NO₃⁻, K⁺) from the metal salt solution, single phase YAG:Tb particles with 20 nm particle size were obtained. The emission spectra of YAG:Tb particles of 14 nm shows a blue shift.     

Novel synthesis method of YAG: Ce micron-sized powders and its luminescence properties

Micron-sized Ce-doped yttrium aluminum garnet (YAG: Ce³⁺) powders are synthesized successfully by a new method including three processes including solvothermal treatment, precursor preheated and annealing treatment in a mild condition. The phase, morphology and luminescent properties are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation (PLE) and photoluminescence (PL) spectra respectively. The single-phase sample can be formed after solvothermal treatment at 180 °C for 12 h and annealing at 1200 °C for 4 h. The results obtained by SEM show that the particles with narrow size distribution (∼4 μm) and nice morphology are formed after annealing treatment. This indicates that it has good homogeneity and dispersion. The micron-sized Ce-doped YAG shows broad emission bands in the range of 500–680 nm with the maximum intensity at 577 nm.     

The photoluminescence properties of Y2O3:Eu prepared by surfactant assisted co-precipitation-molten salt synthesis

Y₂O₃:Eu³⁺ red phosphors were prepared by surfactant assisted co-precipitation-molten salt synthesis method. The effects of surfactant content and annealing temperature on the structure and luminescence were investigated by X-ray diffraction and fluorescence spectrophotometer. The use of surfactant reduces the impurities on the surface of particles and promotes the reaction. The color purity of as-prepared Y₂O₃:Eu³⁺ red phosphors is improved with the presence of surfactant. In the excitation spectra, two strong bands at 394 and 466 nm are attributed to ⁷F_0,1-⁵L₆, ⁷F_0,1-⁵D₂ transitions of Eu³⁺ ions respectively. With the excitation of 394 or 466 nm, the as-fabricated samples reveal excellent red emission as high as that of samples monitored by 254 nm. Thus, the Y₂O₃:Eu³⁺ is a promising red phosphor for ultraviolet-visible light-emitting diodes.     

Photoluminescence properties Pr and Bi-codoped CaTiO3 phosphor prepared by a peroxide-based route

CaTiO₃:Pr³⁺ phosphors codoped with Bi³⁺ ions were synthesized by a peroxide-based route (PBR). The effect of codopants on the structural and luminescence properties was studied. Boric acid used as flux material was proved to be effective in improving the luminescence property. The phosphors prepared by the PBR method showed advantages of lower sintering temperature, shorter heating time, and small grain size. The CaTiO₃:Pr³⁺,Bi³⁺ demonstrated to be a potential red-emitting phosphor for white light-emitting diodes.     

Crystal structure and Eu/Tb doped luminescent properties of a new borate Ba3BiB9O18

Undoped and doped either by Eu³⁺ or Tb³⁺ bismuth borate Ba₃BiB₉O₁₈ was structurally characterized and analyzed by fluorescence spectroscopy. Belonging to synthetic borate member of the family Ba₃XB₉O₁₈, layers of planar triangular B₃O₆ groups connecting with deformed BaO₆ hexagons are interleaved by 9-coordinate Ba atoms, and 6-coordinate Bi atoms. Its crystal structure was determined and refined from powder X-ray diffraction data by the Rietveld method and the results showed that Ba₃BiB₉O₁₈ belongs to space group P6₃/m with unit cell dimensions of a = 7.1999(2) Å, c = 17.3567(6) Å, and z = 2. Curves of differential thermal analysis and thermogravimetric analysis showed that Ba₃BiB₉O₁₈ is a congruent melting compound and chemically stable above 728 °C. Ba₃Bi_1−xEu_xB₉O₁₈ and Ba₃Bi_1−xTb_xB₉O₁₈ form a continuous solid solution from x = 0.01 to x = 0.9. The ultraviolet excited photoluminescence intensity increased with both Eu³⁺ and Tb³⁺ concentration in the matrix of Ba₃BiB₉O₁₈. There may be an interesting correlation between spectroscopic properties and lattice structural features of doped Ba₃BiB₉O₁₈.     

Structural, morphological and optical investigations on BaMgAl10O17:Eu elaborated by a microwave induced solution combustion synthesis

Blue-emitting Eu²⁺-doped barium magnesium aluminate (BaMgAl₁₀O₁₇:Eu²⁺) for advanced displays and lighting devices was prepared by a microwave induced solution combustion synthesis using urea as combustion fuel and nitrates as oxidizer. Purity control of as-synthesized blue phosphor particles was undertaken by modifying the fuel to oxidizer molar ratio. X-ray diffraction, scanning electron microscopy and photoluminescence were used to investigate powders crystallinity, particles size, morphology and luminescent properties, respectively. Fuel-rich urea reactions preferentially lead to pure phases compared to the powders synthesized with a stoichiometric fuel to oxidizer ratio. In both cases, we produce a nearly pure well-crystallized and nanostructured BaMgAl₁₀O₁₇:Eu²⁺. Photoluminescence measurements exhibit the characteristic blue emission of Eu²⁺ under UV light excitation however a weak red emission associated to Eu³⁺ is also detected.     

Synthesis and luminescence properties of novel LiSrPO4:Dy phosphor

Novel LiSrPO₄:Dy³⁺ phosphors for white light-emitting diodes (w-LEDs) were synthesized by the conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation of LiSrPO₄:Dy³⁺ materials. Luminescence properties results showed that the phosphor could be efficiently excited by the UV–vis light region from 250 to 460 nm, and it exhibited blue (483 nm) and yellow (574 nm) emission corresponding to ⁴F_9/2 → ⁶H_15/2 transitions and ⁴F_9/2 → ⁶H₁₃/₂ transitions, respectively. The luminescence intensity of LiSrPO₄:xDy³⁺ phosphor firstly increased and then decreased with increasing Dy³⁺ concentration, and reached the maximum at x = 0.03. It was found that concentration quenching occurred as a result of dipole-dipole interaction according to the Dexter's theory. The decay time was also determined for various concentrations of Dy³⁺ in LiSrPO₄.     

Upconversion white-light emitting of Tm and Er codoped oxyfluoride and its achieving mechanism

Tm³⁺ and Er³⁺ codoped oxyfluoride samples were synthesized by high temperature solid-state reaction. Intense upconversion white light of Tm³⁺ and Er³⁺ codoped oxyfluoride was observed under the excitation of a 980-nm infrared laser diode, which was composed of three primary colors, i.e., blue (from Tm³⁺), green (from Er³⁺), and red emissions (from Tm³⁺ and Er³⁺). The optimal white upconversion light, which is close to the standard achromatic point, was achieved firstly by phase transition from PbO to PbO₂. The scanning electron microscopy, X-ray diffraction and Commission Internationale d’Eclairage chromaticity analysis revealed the dependence of the white upconversion light both on microstructure and Er³⁺ content. The sample with white upconversion light close to the standard achromatic point has potential applications in the fields of the three-dimensional solid-state display and multicolor backlight.     

Synthesis of ultrafine YAG:Tb phosphor by nitrate-citrate sol-gel combustion process

Ultrafine terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders are prepared by a nitrate-citrate sol-gel combustion process using 1:1 ratio of citrate/nitrate. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) techniques. Single-phase cubic YAG:Tb crystalline powder is obtained by calcinating the amorphous materials at 900 °C and no intermediate phase is observed. Transmission electronic microscope (TEM) morphology shows that the resultant YAG:Tb powders have uniform size and good homogeneity. The particle size of the product is investigated as a function of the calcination temperature. The photoluminescence (PL) spectrum of Tb³⁺ substituted for Y³⁺ in YAG with 5.0% content has been measured on samples calcined at different temperatures.     

Synthesis and characterization of IR up-conversion material CaS:Eu, Sm by low-temperature combustion synthesis method

Infrared up-conversion material CaS:Eu, Sm was synthesized by the low-temperature combustion synthesis (LCS) method, which has expanded the application range of the LCS method which is always used in the synthesis of oxides and compound oxides. The combustion process was discussed and the effect of the amount of carbamide on the up-conversion luminescence properties was analyzed. XRD patterns show that the products are with the cubic CaS crystal structure. Spectral analysis indicates that the sample can be excited effectively by ultraviolet or visible light to store energy, and subsequently is sensitive to 800-1600 nm infrared light and then emit red light resulting from the multi-transitions of Eu²⁺ 4f⁶5d → 4f⁷(⁸S_7/2).     

A novel red phosphor for near UV InGaN light-emitting diode and its luminescent properties

A series of new red phosphors, NaEu(MoO₄)_2−2x(SO₄)_2x, were prepared by the conventional solid state reaction. Their excitation spectra, emission spectra and decay curves were measured at room temperature. When the SO₄²⁻ content is in excess of 20%, other phases appear. With the introduction of SO₄²⁻, the Mo-O charge transfer band of NaEu(MoO₄)_2−2x(SO₄)_2x shows red shift, and the excitation intensities of the 4f - 4f transitions of Eu³⁺ are strengthened, compared with that of NaEu(MoO₄)₂. The single red light-emitting diodes-based these phosphors were fabricated. The light-emitting diode fabricated with the phosphor NaEu(MoO₄)_1.80(SO₄)_0.20 exhibited higher red emission relative to that with NaEu(MoO₄)₂. Bright red light can be observed by naked eyes from the light-emitting diode-based NaEu(MoO₄)_1.80(SO₄)_0.20.     

Luminescence properties and energy transfer of a novel bluish-green tunable NaBa4(BO3)3:Ce3+, Tb3+ phosphor

A series of single-phased emission tunable NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors were synthesized by solid-state reaction. The crystal structure, photoluminescence properties, concentration quenching and energy transfer of NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ were systematically investigated. The wavelength-tunable bluish-green light can be realized by coupling the emission bands centered at 425 and 543 nm ascribed to the contribution from Ce³⁺ and Tb³⁺, respectively. The energy transfer from Ce³⁺ to Tb³⁺ in NaBa₄(BO₃)₃ host was studied and demonstrated to be a resonant type via a dipole–dipole interaction mechanism. The energy transfer efficiency (Ce³⁺ → Tb³⁺) obtained by decay curves was consistent with the result calculated by the emission intensity, which gradually increased from 0% to 84.5% by increasing the Tb³⁺ doping content from 0 to 0.45. The results indicate that the NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors have potential applications as an ultraviolet-convertible phosphor due to its effective excitation in the ultraviolet rang.     

Photoluminescence from terbium doped silica-titania prepared by a sol-gel method

Terbium doped (0.5 at.%) TiO₂-SiO₂ (30%/70%) was prepared by a sol-gel method. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the powder calcined at two different temperatures. At a low temperature of 550 °C an amorphous phase was obtained, but at a higher temperature of 1000 °C, the anatase TiO₂ phase was crystallized in the amorphous SiO₂ phase. Green photoluminescence from ultraviolet excitation was detected after heating to either temperature, but the amorphous sample heated to 550 °C exhibited a higher intensity. X-ray diffraction and photoluminescence excitation data are discussed to explain these observations.     

Direct synthesis of strontium titanate phosphor particles with high luminescence by flame spray pyrolysis

SrTiO₃:Pr, Al phosphor particles with high luminescence intensities were directly prepared by flame spray pyrolysis without post-treatment. They had better crystallinity than those prepared by general spray pyrolysis with post-treatment and solid-state reaction methods. In addition, they had complete spherical shape and narrow size distribution. On the other hand, the particles prepared by general spray pyrolysis had irregular shape, and poorer brightness than those prepared by solid-state reaction method, while the particles prepared by flame spray pyrolysis had comparable photoluminescence and cathodoluminescence intensities with those of particles prepared by solid-state reaction method. The photoluminescence intensity of SrTiO₃:Pr, Al particles prepared by flame spray pyrolysis was as much as 4.7 times higher than that of particles prepared by general spray pyrolysis.     

Malayaite ceramic pigments: A combined optical spectroscopy and neutron/X-ray diffraction study

Ceramic pigments based on the Cr-doped malayaite structure were synthesized by solid state reaction and characterized by optical spectroscopy and combined X-ray and neutron powder diffraction in order to elucidate the still unclear chromium substitution mechanisms. The results show that coloration is actually due to simultaneous occurrence of Cr⁴⁺ and Cr³⁺ ions in the crystal lattice. Spectroscopy data confirm that Cr⁴⁺ is replacing Sn⁴⁺ in the octahedral site and, in minor amount, Si⁴⁺ in the tetrahedral site. In addition, neutron powder diffraction data suggest that Cr³⁺ substitution for octahedral Sn⁴⁺ is charge balanced by the formation of oxygen vacancies with no preference over the different oxygen sites. Upon incorporation of Cr ion, the SnO₆ octahedra exhibit an off-centre displacement of central cation which in turn induces a rearrangement of both the octahedral and tetrahedral coordination shells.     

Luminescence response and CL degradation of combustion synthesized spherical SiO2:Ce nanophosphor

This study was aimed to systematically investigate the luminescence response of SiO₂:Ce³⁺ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO₂:Ce_1m% samples were also annealed at 1000 °C for 1 h in a charcoal environment to reduce incidental Ce⁴⁺ to partial Ce³⁺ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3-8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO₂ was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO₂:Ce³⁺ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO₂:Ce³⁺ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO₂:Ce³⁺ annealed at 1000 °C were obtained.     

Europium-doped yttrium silicate nanophosphors prepared by flame synthesis

Europium-doped yttrium silicate (Y₂SiO₅:Eu³⁺) nanophosphors were successfully synthesized by flame spray pyrolysis method. The effect of silicon concentration on the crystal structure and morphology of the Y₂SiO₅:Eu³⁺ phosphors were investigated. As-prepared phosphor consists of spherical nanoparticles with filled morphology, high crystallinity, narrow size distribution, and intense photoluminescence. The crystal structure and photoluminescence intensity of Y₂SiO₅:Eu³⁺ nanophosphors are strongly affected by the ratio of silicon to yttrium in the precursor solution, and the maximum photoluminescence intensity is obtained from particles prepared from the silicon to yttrium ratio of 1.25. A concentration quenching limit is observed at 30 mol% Eu of yttrium. The photoluminescence intensity also increases with the increase of the concentration of precursor solution. This work demonstrates the advantages of flame spray pyrolysis method for the preparation of multi-component nanophosphor, which can be found potential application in lamp and display industries.