Solvothermal synthesis and luminescent properties of monodisperse LaPO4:Ln (Ln=Eu, Ce, Tb) particles

Monodisperse rare-earth ion (Eu³⁺, Ce³⁺, Tb³⁺) doped LaPO₄ particles with oval morphology were successfully prepared through a facile solvothermal process without further heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra and the kinetic decays were performed to characterize these samples. The XRD results reveal that all the doped samples are well crystalline at 180 °C and assigned to the monoclinic monazite-type structure of the LaPO₄ phase. It has been shown that all the as-synthesized samples show perfectly oval morphology with narrow size distribution. The possible growth mechanism of the LaPO₄:Ln has been investigated as well. Upon excitation by ultraviolet radiation, the LaPO₄:Eu³⁺ phosphors show the characteristic ⁵D₀−⁷F_1-4 emission lines of Eu³⁺, while the LaPO₄:Ce³⁺, Tb³⁺ phosphors demonstrate the characteristic ⁵D₄−⁷F_3-6 emission lines of Tb³⁺.     

Fabrication and luminescent properties of the core-shell structured YNbO4:Eu/Tb@SiO2 spherical particles

The core-shell structured YNbO₄:Eu³⁺/Tb³⁺@SiO₂ particles were realized by coating the YNbO₄:Eu³⁺/Tb³⁺ phosphors onto the surface of spherical silica via a sol-gel process. The obtained materials were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra. The results indicate that 600 °C annealed samples consist of amorphous silica core and crystalline YNbO₄:Re shell, having perfect spherical morphology with uniform size distribution. Upon excitation by UV or electron beam, these phosphors show the characteristic ⁵D₀-⁷F_1-4 emission lines of Eu³⁺ and the characteristic ⁵D₄-⁷F_3-6 emission lines of Tb³⁺. The PL intensities of Eu³⁺ can be tuned by altering the annealing temperature and the coating number of YNbO₄:Eu³⁺ layers.     

Hydrothermal synthesis and luminescent properties of LuBO3:Tb microflowers

Hexagonal vaterite-type LuBO₃:Tb³⁺ microflower-like phosphors have been successfully prepared by an efficient surfactant- and template-free hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometry, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-obtained phosphor samples present flowerlike agglomerates composed of nanoflakes with thickness of 40 nm and high crystallinity in spite of the moderate reaction temperature of 200 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. Under ultraviolet excitation into the 4f⁸→4f⁷5d transition of Tb³⁺ at 248 nm (or 288 nm) and low-voltage electron beam excitation, LuBO₃:Tb³⁺ samples show the characteristic green emission of Tb³⁺ corresponding to ⁵D₄→⁷F_{6, 5, 4, 3} transitions with the ⁵D₄→⁷F₅ transition (542 nm) being the most prominent group, which have potential applications in fluorescent lamps and field emission displays.     

Hydrothermal synthesis and luminescent properties of Sb-doped Sr3(PO4)2

Sb³⁺-doped Sr₃(PO₄)₂ crystals has been synthesized using phosphoric acid, strontium hydroxide and antimony powder as the raw materials through a hydrothermal reaction method. The crystallinity and the microstructure were investigated using X-ray diffraction and scanning electron microscopy. The photoluminescent property was investigated using luminescent spectrometer. Phase pure Sr₃(PO₄)₂ crystal was obtained and it has a shape of hexagonal rod. It showed the emission and excitation peaks at 396, 250, and 215 nm, respectively, indicating that the emission is attributed to ³P₁-¹S₀ transition and the excitation is attributed to ¹S₀-³P₁ and ¹S₀-¹P₁ transition. It was also observed that the intensity of photoluminescence is thermally stable up to 673 K.     

A new promising phosphor, Na3La2(BO3)3:Ln (Ln=Eu, Tb)

We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na₃La₂(BO₃)₃ (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb³⁺ and Eu³⁺)-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb³⁺, Eu³⁺) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu³⁺ ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613 nm, which is attributed to ⁵D₀-⁷F₂ transition of Eu³⁺. The luminescence indicates that the local symmetry of Eu³⁺ in NLBO crystal lattice has no inversion center. Optimum Eu³⁺ concentration of NLBO:Eu³⁺ under UV excitation with 395 nm wavelength is about 30 mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252 nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb³⁺ in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb³⁺ and Eu³⁺) was analyzed. The relative high quenching concentration was also discussed.     

Solvothermal synthesis and luminescence properties of monodisperse Gd2O3:Eu and Gd2O3:Eu@SiO2 nanospheres

A series of uniform, monodispersed Gd(OH)³:Eu³⁺ nanospheres less than 100 nm were successfully synthesized with iron ions as catalyst and DMF as solvent under the solvothermal condition. Cetyltrimethyl ammonium bromide (CTAB) and Polyvinylpyrrolidone (PVP) were performed as co-surfactant during this facile procedure should be changed as A series of uniform, monodisperse Gd(OH)³:Eu³⁺ nanospheres less than 100 nm in diameter were successfully synthesized with solvothermal method. Iron ion was used as catalyst and Dimethylformamide (DMF) as solvent, Cetyltrimethyl Ammonium Bromide (CTAB) and Polyvinylpyrrolidone (PVP) were performed as surfactants. Further calcination process was applied to prepare Gd₂O₃:Eu³⁺ nanoshpheres during this facile procedure.     

Sn4As3 revisited: Solvothermal synthesis and crystal and electronic structure

A facile one pot method of synthesis of tin arsenide Sn₄As₃ starting from metallic tin and elemental arsenic under mild solvothermal conditions in ethylenediamine in the presence of ammonium chloride is offered. The dissolving of the tin metal in ethylenediamine and the role of NH₄Cl are discussed. The crystal structure of Sn₄As₃ has been re-determined. It is shown to crystallize in the trigonal non-centrosymmetric space group R3m, (a=4.089(1) Å, c=36.059(6) Å, Z=3), which differs from the previously reported centrosymmetric structure . The crystal structure of Sn₄As₃ consists of alternating layers of arsenic and tin atoms that are combined into seven-layer blocks and build up along the c-axis. The major structural feature is the short tin-tin distances (3.24 Å) between the adjacent blocks. The analysis of the density of states and band structure reveals that Sn₄As₃ should have metallic properties, which is in line with the previously reported experimental observations. Analysis of chemical bonding employing the electron localization function shows that only for the shortest Sn-As contacts the bonding is pairwise, while four-center bonds are formed between arsenic and tin atoms at relatively long distances (>2.85 Å). Moreover, each tin atom holds an electron lone-pair.     

Synthesis, vacuum ultraviolet and near ultraviolet-excited luminescent properties of GdCaAl3O7: RE (RE=Eu, Tb)

Vacuum ultraviolet (VUV) excitation and photoluminescent (PL) properties of Eu³⁺ and Tb³⁺ ion-doped aluminate phosphors, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ have been investigated. X-ray diffraction (XRD) patterns indicate that the phosphor GdCaAl₃O₇ forms without impurity phase at 900 °C. Field emission scanning electron microscopy (FE-SEM) images show that the particle size of the phosphor is less than 3 μm. Upon excitation with VUV irradiation, the phosphors show a strong emission at around 619 nm corresponding to the forced electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺, and at around 545 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺. The results reveal that both GdCaAl₃O₇:RE³⁺ (RE=Eu, Tb) are potential candidates as red and green phosphors, respectively, for use in plasma display panel (PDP).     

不同形貌的SrMoO_4材料的微乳液及其辅助的溶剂热法制备

通过微乳液法及其辅助的溶剂热法制备出了不同形貌的SrMoO4粉体材料,探讨了工艺参数对SrMoO4材料形貌的影响。微乳液体系中表面活性剂十六烷基三甲基溴化铵(CTAB)浓度、反应物浓度及溶剂热过程中反应时间、CTAB浓度都会对SrMoO4材料的形貌造成影响。通过调整上述工艺参数可以调控SrMoO4材料的形貌,得到了近球状、哑铃状、纺锤体状、花簇状等特殊形貌的SrMoO4微晶材料。SrMoO4样品的室温光致发光谱是由发光中心在约420nm处的单一紫光组成,样品的形貌不同发光强度和发光峰位置略有不同。     

Structural studies of five layer Aurivillius oxides: A2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A₂Bi₄Ti₅O₁₈ (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi₂O₂]²⁺ layers interleaved with perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks. The structures were refined in the orthorhombic space group B2eb (SG. No. 41), Z=4, and the unit cell parameters of the oxides are a=5.4251(2), b=5.4034(1), c=48.486(1); a=5.4650(2), b=5.4625(3), c=48.852(1); a=5.4988(3), b=5.4980(4), c=50.352(1); a=5.4701(2), b=5.4577(2), c=49.643(1) for A=Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n=2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi₂O₂]²⁺ layers and perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks were relieved by tilting of the TiO₆ octahedra. Variable temperature synchrotron X-ray studies for Ca and Pb compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented.     

Synthesis of the complex fluoride LiBaF3 and optical spectroscopy properties of LiBaF3:M(M=Eu,Ce) through a solvothermal process

The complex fluoride LiBaF₃ and LiBaF₃:M(M=Eu, Ce) is solvothermally synthesized at 180°C and characterized by means of X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy. In the solvothermal process, the solvents, molar ratios of initial mixtures and reaction temperature play important roles in the formation of products. The excitation and emission spectra of the LiBaF₃:M(M=Eu,Ce) have been measured by fluorescence spectrophotometer. In the LiBaF₃:Eu emission spectra, there is one sharp line emission located at 360 nm arising from f→f transition of Eu²⁺ in the host lattice, and typical doublet 5d-4f emission of Ce³⁺ in LiBaF₃ powder is shown.     

Luminescence of NaGdFPO4:Ln after VUV excitation: A comparison with GdPO4:Ln (Ln=Ce, Tb)

The phosphors NaGdFPO₄:Ln³⁺ and GdPO₄:Ln³⁺ (for Ln³⁺=Ce³⁺ and Tb³⁺) were prepared by solid-state reaction technique, the VUV-vis spectroscopic properties of the phosphors were investigated, and we vividly compare the luminescence of Ce³⁺ and Tb³⁺ in the hosts. For phosphors GdPO₄:Ln³⁺, the band near 155 nm in VUV excitation spectrum is assumed to be the host-related absorption, and for NaGdFPO₄:Ln³⁺ the absorption is moved to longer wavelength, near 170 nm, showing the P-O bond covalency increased after fluoridation. The f-d transitions of Ce³⁺ and Tb³⁺ in the host lattices are assigned and corroborated, and it was found that the 5d states are with lower energy in NaGdFPO₄:Ln³⁺ than those in GdPO₄:Ln³⁺. For fluoridation of GdPO₄:Ln³⁺ to NaGdFPO₄:Ln³⁺, the energy change of Ln³⁺ (Ln=Ce, Tb) 5d states is consistent with that of host-related absorption.     

Photoluminescence properties of a novel phosphor, Na3La9O3(BO3)8:RE(RE=Eu,Tb)

The new oxyborate phosphors, Na₃La₉O₃(BO₃)₈:Eu³⁺ (NLBO:Eu) and Na₃La₉O₃(BO₃)₈:Tb³⁺ (NLBO:Tb) were prepared by solid-state reactions. The photoluminescence characteristics under UV excitation were investigated. The dominated emission of Eu³⁺ corresponding to the electric dipole transition ⁵D₀→⁷F₂ is located at 613 nm and bright green luminescence of NLBO:Tb attributed to the transition ⁵D₄→⁷F₅ is centered at 544 nm. The concentration dependence of the emission intensity showed that the optimum doping concentration of Eu and Tb is 30% and 10%, respectively.     

Sol-gel deposition and luminescent properties of LaMgAl11O19:Ce/Tb phosphor films

Rare earth ions (Ce³⁺, Tb³⁺)-doped LaMgAl₁₁O₁₉ phosphor films were deposited on quartz glass substrates by Pechini sol-gel and dip coating method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM), field emission scanning electronic microscopy (FESEM), photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the magnetoplumbite structure LaMgAl₁₁O₁₉ phase can be obtained at 1200 °C on quartz glass substrates. This was further verified by the results of FT-IR and TG-DTA. AFM study showed that uniform films have an average grain size of 150 nm and a root mean square (RMS) roughness of 4 nm. The thickness of the films characterized by FESEM is about 340 nm. LaMgAl₁₁O₁₉:Ce³⁺ film showed the parity and spin allowed 5d-4f band emission of Ce³⁺ with a maximum at 350 nm. Ce³⁺, Tb³⁺-codoped LaMgAl₁₁O₁₉ films showed the band emission of Ce³⁺ and characteristic emission of Tb³⁺, namely, ⁵D_3,4-⁷F_J (J=6, 5, 4, 3) due to an efficient energy transfer from Ce³⁺ to Tb³⁺ in the host.     

Photoluminescence properties of BaMoO4 amorphous thin films

BaMoO₄ amorphous and crystalline thin films were prepared from polymeric precursors. The BaMoO₄ was deposited onto Si wafers by means of the spinning technique. The structure and optical properties of the resulting films were characterized by FTIR reflectance spectra, X-ray diffraction (XRD), atomic force microscopy (AFM) and optical reflectance. The bond Mo-O present in BaMoO₄ was confirmed by FTIR reflectance spectra. XRD characterization showed that thin films heat-treated at 600 and 200 °C presented the scheelite-type crystalline phase and amorphous, respectively. AFM analyses showed a considerable variation in surface morphology by comparing samples heat-treated at 200 and 600 °C. The reflectivity spectra showed two bands, positioned at 3.38 and 4.37 eV that were attributed to the excitonic state of Ba²⁺ and electronic transitions within MoO²⁻₄, respectively. The optical band gaps of BaMoO₄ were 3.38 and 2.19 eV, for crystalline (600 °C/2 h) and amorphous (200 °C/8 h) films, respectively. The room-temperature luminescence spectra revealed an intense single-emission band in the visible region. The PL intensity of these materials was increased upon heat-treatment. The excellent optical properties observed for BaMoO₄ amorphous thin films suggested that this material is a highly promising candidate for photoluminescent applications.     

Tunable photoluminescence of NaYF4:Eu nanocrystals by Sr codoping

NaYF₄:Eu/Sr nanocrystals were synthesized by a hydrothermal method. Tunable photoluminescence of the NaYF₄:Eu nanocrystals was successfully achieved by codoping with Sr²⁺ ions. With increasing Sr²⁺ concentration, not only the X-ray diffraction peaks of the nanocrystals become broader, but also the positions of them shift toward larger lattice parameters. Eu³⁺ and Eu²⁺ have been found to coexist in an NaYF₄:Eu/Sr. The Eu³⁺/Eu²⁺ emission intensity ratio changed with the Sr²⁺ concentration and excitation wavelength. More interestingly, the spectral configurations of Eu²⁺ and Eu³⁺ also varied with the excitation wavelength, indicating that the nanocrystals have multiple luminescence centers or emitting states.     

Syntheses and characterization of two oxoborates, (Pb3O)2(BO3)2MO4 (M=Cr, Mo)

Two oxoborates, (Pb₃O)₂(BO₃)₂MO₄ (M=Cr, Mo), have been prepared by solid-state reactions below 700 °C. Single-crystal XRD analyses showed that the Cr compound crystallizes in the orthorhombic group Pnma with a=6.4160(13) Å, b=11.635(2) Å, c=18.164(4) Å, Z=4 and the Mo analog in the group Cmcm with a=18.446(4) Å, b=6.3557(13) Å, c=11.657(2) Å, Z=4. Both compounds are characterized by one-dimensional chains formed by corner-sharing OPb₄ tetrahedra. BO₃ and CrO₄ (MoO₄) groups are located around the chains to hold them together via Pb–O bonds. The IR spectra further confirmed the presence of BO₃ groups in both structures and UV–vis diffuse reflectance spectra showed band gaps of about 1.8 and 2.9 eV for the Cr and Mo compounds, respectively. Band structure calculations indicated that (Pb₃O)₂(BO₃)₂MoO₄ is a direct semiconductor with the calculated energy gap of about 2.4 eV.     

Reduction of Eu to Eu in MAl2Si2O8 (M=Ca, Sr, Ba) in air condition

In general, the reduction of Eu³⁺ to Eu²⁺ in solids needs an annealing process in a reducing atmosphere. In this paper, it is of great interest and importance to find that the reduction of Eu³⁺ to Eu²⁺ can be realized in a series of alkaline-earth metal aluminum silicates MAl₂Si₂O₈ (M=Ca, Sr, Ba) just in air condition. The Eu²⁺-doped MAl₂Si₂O₈ (M=Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong band emissions of 4f⁶5d¹-4f⁷ from Eu²⁺ were observed at 417, 404 and 373 nm in air-annealed CaAl₂Si₂O₈, SrAl₂Si₂O₈ and BaAl₂Si₂O₈, respectively, under ultraviolet excitation although the Eu³⁺ precursors were employed. In addition, under low-voltage electron beam excitation, Eu²⁺-doped MAl₂Si₂O₈ also shows strong blue or ultraviolet emission corresponding to 4f⁶5d¹-4f⁷ transition. The reduction mechanism from Eu³⁺ to Eu²⁺ in these compounds has been discussed in detail.     

Photoluminescent BaMoO4 nanopowders prepared by complex polymerization method (CPM)

The BaMoO₄ nanopowders were prepared by the Complex Polymerization Method (CPM). The structure properties of the BaMoO₄ powders were characterized by FTIR transmittance spectra, X-ray diffraction (XRD), Raman spectra, photoluminescence spectra (PL) and high-resolution scanning electron microscopy (HR-SEM). The XRD, FTIR and Raman data showed that BaMoO₄ at 300 °C was disordered. At 400 °C and higher temperature, BaMoO₄ crystalline scheelite-type phases could be identified, without the presence of additional phases, according to the XRD, FTIR and Raman data. The calculated average crystallite sizes, calculated by XRD, around 40 nm, showed the tendency to increase with the temperature. The crystallite sizes, obtained by HR-SEM, were around of 40-50 nm. The sample that presented the highest intensity of the red emission band was the one heat treated at 400 °C for 2 h, and the sample that displayed the highest intensity of the green emission band was the one heat treated at 700 °C for 2 h. The CPM was shown to be a low cost route for the production of BaMoO₄ nanopowders, with the advantages of lower temperature, smaller time and reduced cost. The optical properties observed for BaMoO₄ nanopowders suggested that this material is a highly promising candidate for photoluminescent applications.     

Solvothermal synthesis and photoluminescence properties of BiPO4 nano-cocoons and nanorods with different phases

Hexagonal phase BiPO₄ nano-cocoons and monoclinic phase BiPO₄ nanorods have been synthesized in the mixed solvents of glycerol and distilled water with the volume ratio of 2:1 at 200 °C. The solvothermal evolution process from hexagonal phase BiPO₄ nano-cocoons to monoclinic phase BiPO₄ nanorods was observed by varying the reaction time from 1 to 3 h. In the hydrothermal condition at 160 °C, the similar phase transformation from hexagonal phase BiPO₄ to monoclinic phase BiPO₄ was also observed, accompanying with a morphology transformation from nanorods to octahedron-like microcrystals. It was found that the volume ratio of glycerol to water in the solvothermal condition had a great impact on the shapes of products, while it had no influence on the formation of different phases. The fluorescence spectra of hexagonal phase BiPO₄ nano-cocoons and monoclinic phase BiPO₄ nanorods were also studied.