Observation of broadband infrared luminescence in a novel Bi-doped P2O5-B2O3-Al2O3 glass

A novel Bi-doped P₂O₅-B₂O₃-Al₂O₃ glass was investigated, and strong broadband NIR (near infrared) luminescence was observed when the sample was excited by 445 nm, 532 nm, 808 nm and 980 nm lasers, respectively. The max FWHM with 312 nm, the lifetime with 580 μs and the σ_emτ product with 5.3 × 10^− 24 cm² s were obtained which indicates that this glass is a promising material for broadband optical amplifier and tunable laser. The effect of the introduction of B₂O₃ on the glass structure and Bi-ions illuminant mechanism were discussed and analyzed. It is suggested that the introduction of B₂O₃ makes the glass structure closer, and the broadband NIR emission derives from Bi⁰:²D_3/2 → ⁴S_3/2 and Bi⁺:³P₁ → ³P₀ transitions.     

Multi-color long-lasting phosphorescence in Mn-doped ZnO-B2O3-SiO2 glass-ceramics

Multi-color LLP phenomenon was observed in Mn²⁺-doped ZnO-B₂O₃-SiO₂ glass-ceramics after the irradiation of a UV lamp at room temperature. Transparent ZnO-B₂O₃-SiO₂ glass emitted reddish LLP while opaque glass-ceramics prepared by the glass sample after heat treatment emitted yellowish or greenish LLP. The change of the phosphorescence is due to the alteration of co-ordination state of Mn²⁺. The phosphorescence of the samples was seen in the dark with naked eyes even 12 h after the irradiation with a UV lamp (λ_max=254 nm) for 30 min. Based on the approximative t⁻¹ decay law of the phosphorescence, we suggest that the LLP is attributed to the thermally assisted electron-hole recombination.     

Synthesis and Li ion conductivity of Li2O-Nb2O5-P2O5 glasses and glass-ceramics

Glasses with the compositions of xLi₂O-(70 − x)Nb₂O₅-30P₂O₅, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li⁺ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li⁺ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li₂O content, and the glass of 60Li₂O-10Nb₂O₅-30P₂O₅ shows the value of σ = 2.35 × 10⁻⁶ S/cm at room temperature and the activation energy (E_a) of 0.48 eV for Li⁺ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li₃PO₄ and NbPO₅ are formed in the crystallization of the glasses and the crystallization results in the decrease in Li⁺ ion conductivity in all samples, indicating that any high Li⁺ ion conducting crystalline phases have not been formed in the present glasses. 60Li₂O-10Nb₂O₅-30P₂O₅ glass shows a bulk nanocrystallization (Li₃PO₄ nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10⁻⁷ S/cm at room temperature and E_a = 0.49 eV.     

Preparation and characterization of Co-doped ZnO-Al2O3-SiO2 glass-ceramics by the sol-gel method

Transparent glass-ceramics containing Co²⁺:ZnAl₂O₄ nanocrystals were obtained by the sol-gel process for the first time. The gels of composition 89SiO₂-5.9Al₂O₃-4.9ZnO-0.2CoO (ZAS) were prepared at room temperature, and heat-treated at different temperatures. The microstructure and optical properties of the heated samples were studied by using X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy, and optical absorption spectra. Co²⁺:ZnAl₂O₄ nanocrystals were precipitated from ZAS system and dispersed in the SiO₂-based glass during heat-treatment in the temperature range 900-1100 °C. Co²⁺ ions were located in tetrahedral sites in ZnAl₂O₄ nanocrystals. The Co²⁺:ZnAl₂O₄ crystallite size was in the range of 4-15 nm.     

A red-emitting phosphor of fully concentrated Eu-based molybdenum borate Eu2MoB2O9

The fully concentrated Eu³⁺-based molybdenum borate Eu₂MoB₂O₉ was synthesized by the solid-state reaction method. The photoluminescence excitation and emission spectra, the temperature dependent luminescence intensities and the decay curve were investigated. Photoluminescence spectra show that the phosphor can be efficiently excited by near-UV light and exhibits an intense red luminescence corresponding to the electric dipole transition ⁵D₀ → ⁷F₂ at 615 nm. The luminescence intensities and color purity were investigated by increasing the fired temperatures. The phosphor shows the stable luminescence and color purity at high temperature.     

A novel broadband emission phosphor Ca2KMg2V3O12 for white light emitting diodes

A novel broadband emission phosphor Ca₂KMg₂V₃O₁₂ was first synthesized by solution combustion method. The X-ray diffraction showed that Ca₂KMg₂V₃O₁₂ phase can be obtained at 600-900 °C through combustion route. The crystal structure of this material was refined by Rietveld method using powder X-ray diffraction. It crystallizes in cubic system and belongs to space group Ia3d with z = 8, a = 0.12500 nm. The excitation band of Ca₂KMg₂V₃O₁₂ peaks at 320 nm in a region between 260 nm and 425 nm, and the emission spectrum exhibits an intense band centered at about 528 nm covering from 400 nm to 800 nm. The colour coordinates of samples prepared at different ignition temperatures are in a range of x = 0.323-0.339, y = 0.430-0.447.     

Eu ions and CaF2-containing transparent glass-ceramics

Transparent glass-ceramics have been prepared by heat-treating 45SiO₂-20Al₂O₃-10CaO-25CaF₂ glasses doped with Eu²⁺ ions (in mol%). The precipitated crystalline phase in the glass-ceramics was CaF₂. TEM observation showed the precipitated crystalline phase had a size of 11-18 nm and dispersed in the amorphous phase without clustering. Fluorescence measurements showed that Eu²⁺ ions entered into the CaF₂ crystalline phase and gave a much stronger emission in the glass-ceramics than in the corresponding glass.     

Preparation of In2O3 octahedrons by heating InCl3 aqueous solution on the Si substrate

In₂O₃ octahedrons have been synthesized by heating InCl₃ aqueous solution on the Si substrate at 400-900 °C for 2 h. The average size of In₂O₃ octahedrons is decreased by increasing the heating temperature. The In₂O₃ octahedrons are single-crystalline with the body-centered cubic structure and have controllable sizes in the range of 0.7-1.0 μm. A possible mechanism was also proposed to account for the formation of In₂O₃ octahedrons. A strong photoluminescence with a peak at 458 nm was observed from the In₂O₃ octahedrons at room temperature. This emission can be attributed to oxygen vacancies and indium-oxygen vacancy centers.     

Novel Dy-doped Ca2Gd8(SiO4)6O2 white light phosphors for Hg-free lamps application

The luminescent properties of Ca₂Gd_8(1−x)(SiO₄)₆O₂:xDy³⁺ (1% ≤ x ≤ 5%) powder crystals with oxyapatite structure were investigated under vacuum ultraviolet excitation. In the excitation spectrum, the peaks at 166 nm and 191 nm of the vacuum ultraviolet region can be assigned to the O²⁻ → Gd³⁺, and O²⁻ → Dy³⁺ charge transfer band respectively, which is consistent with the theoretical calculated value using Jφrgensen's empirical formula. While the peaks at 183 nm and 289 nm are attributed to the f-d spin-allowed transitions and the f-d spin-forbidden transitions of Dy³⁺ in the host lattice with Dorenbos's expression. According to the emission spectra, all the samples exhibited excellent white emission under 172 nm excitation and the best calculated chromaticity coordinate was 0.335, 0.338, which indicates that the Ca₂Gd₈(SiO₄)₆O₂:Dy³⁺ phosphor could be considered as a potential candidate for Hg-free lamps application.     

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.     

Hydrothermal synthesis and photoluminescence properties of Gd2Zr2O7:Tb phosphors

This paper presents hydrothermal synthesis, characterization, and photoluminescence (PL) properties of novel green-emitting phosphors, Gd₂Zr₂O₇:Tb³⁺. Their crystal structure, morphology and photoluminescence properties were investigated by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and fluorescence spectrophotometer. The results revealed that one-dimensional Gd₂Zr₂O₇:Tb³⁺ nanorods with diameter of about 30 nm and length of 150-300 nm were formed, and the products exhibited a fluorite-type structure. PL study revealed that Gd₂Zr₂O₇:Tb³⁺ phosphors presented dominant green emission luminescence, which was attributed to the transitions from ⁵D₄ excited states to ⁷F_J (J = 3-6) ground states of Tb³⁺. The luminescence intensity of Gd₂Zr₂O₇:Tb³⁺ with different Tb³⁺ concentration was also investigated and reported, and an obvious concentration quenching was observed when Tb³⁺ ion concentration was 5 at.%.     

High pressure luminescence and time resolved spectra of La2Be2O5:Pr

We present luminescence, luminescence excitation and luminescence time resolved spectra of La₂Be₂O₅:Pr³⁺ system. We used high pressure spectroscopy approaches, with high pressure applied in diamond anvil cell (DAC) and sapphire anvil cell (SAC), for detailed analysis of luminescence related to the 4f5d → 4f² and 4f² → 4f² transitions. We present effect of up-converted luminescence related to 4f5d → 4f² transition excited with 488 nm. We also discussed possibility of existence of praseodymium trapped exciton (PTE) states in La₂Be₂O₅:Pr³⁺ system. Lack of the PTE is attributed to high quantity of bulk modulus of this material.     

Multiferroic properties of Pb2Fe2O5 ceramics

Pb₂Fe₂O₅ (PFO) powders in monoclinic structure have been synthesized using lead acetate in glycerin and ferric acetylacetonate as the precursor. The powders were pressed into pellets, which were sintered into ceramics at 800 °C for 1 h. The morphology and structure have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Polarization was observed in Pb₂Fe₂O₅ ceramics at room temperature, exhibiting a clear ferroelectric hysteresis loop. The remanent polarization of Pb₂Fe₂O₅ ceramic is estimated to be Pr ∼ 0.22 μC/cm². The origin of the polarization may be attributed to the off-centers of shifted Pb²⁺ ions as well as the FeO₆ octahedra in the perovskite-based structure of Pb₂Fe₂O₅. Magnetic hysteresis loop was also observed at room temperature. The Pb₂Fe₂O₅ ceramic shows coexistence of ferroelectricity and ferromagnetism. It provides a new field of research for complex oxides with multiferroic properties.     

Transport properties and thermal expansion of La2Mo2O9-based solid electrolytes

The oxygen ion transference numbers of La_1.7Bi_0.3Mo₂O₉, La₂Mo_1.7W_0.3O₉ and La₂Mo_1.95V_0.05O₉ ceramics, determined by modified faradaic efficiency and e.m.f. methods at 973-1173 K, vary in the range 0.995-0.977 in air, decreasing when temperature increases. The activation energies for the ionic and electronic transport are 61-71 kJ/mol and 123-141 kJ/mol, respectively. Reducing oxygen chemical potential leads to increasing n-type electronic contribution to the total conductivity, which remains, however, essentially p(O₂)-independent down to oxygen pressures of 10⁻⁴-10⁻³ atm and exhibits reversible drop on further reduction, probably due to phase decomposition. Doping La₂Mo₂O₉ with calcium results in segregation of a CaMoO₄-based phase, accompanied with increasing electronic transport. The average thermal expansion coefficients of La₂Mo₂O₉-based materials, calculated from dilatometric data in air, are (14.4-14.8) × 10⁻⁶ K⁻¹ at 300-700 K and (16.4-22.5) × 10⁻⁶ K⁻¹ at 700-1070 K.     

Preparation and characterization of porous ultrafine Fe2O3 particles

Porous ultrafine Fe₂O₃ particles were prepared by homogeneous precipitation method. Fe³⁺ and urea were chosen as starting materials and anionic surfactant as the template. It is shown that the reaction results in the precipitation of a gelatinous hydrous iron oxide/surfactant mixture, which gives ultrafine Fe₂O₃ particles after drying and calcinations. The products were characterized by XRD, TEM, TG/DTA and BET. Conventional XRD patterns show that the products are mixture of γ-Fe₂O₃ and α-Fe₂O₃ phase after being sintered at 350 °C, and γ-Fe₂O₃ transforms entirely to α-Fe₂O₃ when sintered at 650 °C. The low-angle XRD patterns indicate that the mesostructure can only exist between 350 and 400 °C. TEM results show that the Fe₂O₃ particles have diameters of about 30 nm and lengths ranging from 100 to 120 nm; in each particle, there are several vermiculate-like mesopores with diameter of about 20-25 nm. The BET surface areas in excess of 50 m²/g are obtained after calcinations at 350 °C. The BJH desorption average pore width is around 22 nm, which is in agreement with the TEM results. The results show that anionic surfactant and sintering temperature are important to obtain this special morphology.     

Luminescent properties of Gd2Ti2O7: Eu phosphor films prepared by sol-gel process

Gd₂Ti₂O₇: Eu³⁺ thin film phosphors were fabricated by a sol-gel process. X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 800 °C and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. The doped Eu³⁺ showed orange-red emission in crystalline Gd₂Ti₂O₇ phosphor films due to an energy transfer from Gd₂Ti₂O₇ host to them. Both the lifetimes and PL intensity of the Eu³⁺ increased with increasing the annealing temperature from 800 to 1000 °C, and the optimum concentrations for Eu³⁺ were determined to be 9 at.%. of Gd³⁺ in Gd₂Ti₂O₇ film host.     

Synthesis and luminescent properties of ZnNb2O6 nanocrystals for solar cell

The phase formation, morphology and luminescent properties of ZnNb₂O₆ nanocrystals by the sol-gel method were investigated at a lower temperature than that of the traditional solid-state reaction method. The products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), photoluminescence spectroscopy (PL) and absorption spectra. The activation energy of ZnNb₂O₆ grain growth is obtained about 18.4 kJ/mol. The diameters of the nanocrystals are in the range of 20-40 nm. The PL spectra excited at 276 nm have a broad and strong blue emission band maximum at 450 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectrum of the sample at a calcination temperature of 800 °C has a band gap energy of 3.68 eV.     

Hydrothermal synthesis of nanocrystalline VO2 from poly(diallyldimethylammonium) chloride and V2O5

Novel vanadium dioxide nanorods were fabricated from V₂O₅ in the presence of a reducing agent, the poly(diallyldimethylammonium chloride) (PDDA) via a hydrothermal method at 180 °C for 48 h. The samples produced were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), nitrogen adsorption (BET) and thermogravimetry (TG/DTG). The nanorods obtained are approximately 50 nm wide and from 300 to 500 nm long and presents high surface area (42 m² g⁻¹). The nanocrystalline B phase VO₂ is not produced by hydrothermal treatment in the absence of the PDDA polyelectrolyte.     

Luminescence quenching processes in Gd2O2S:Pr,Ce scintillating ceramics

Temperature dependent radioluminescence under X-ray excitation (XRL) and luminescence decay time measurements following 430 nm laser excitation have been performed in the 10-775 K range on Gd₂O₂S:Pr³⁺,Ce³⁺ scintillating ceramics. From 200 K to both low and high temperature, XRL light yield decreases by 60%. High temperature luminescence quenching has been revisited. Temperature dependent lifetime measurements imply non-radiative de-excitation mechanism at electronic defects spatially correlated to Pr³⁺ emitting ions. At low temperatures, decreasing XRL light yield with irradiation time is linked to very intense thermoluminescence (TL) peak around 120 K ascribed to sulfur vacancies. These traps cause efficient electron trapping which competes with the prompt recombination mechanism.