Energy transfer and photoluminescent analysis of a novel color-tunable Ba2Y1-xV3O11:xSm3+ nanophosphor for single-phased phosphor-converted white LEDs

Metal nitrates are used to synthesize a series of novel Ba₂Y_1-xV₃O₁₁:xSm³⁺ nanophosphors via urea-assisted solution combustion route. X-ray diffraction (XRD), diffuse reflectance (DR), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were employed to analyse the structure, morphology, photoluminescent behaviour and energy transfer mechanism. Rietveld analysis over Ba₂Y_0.98Sm_0.02V₃O₁₁ showed that Y³⁺ ions can be well-replaced by trivalent samarium ions without resulting any major alteration in the crystal structure of host lattice. Furthermore, the lattice parameters were determined for both the host as well as the doped composition. The Scherrer equation yielded an average particle size of 44?nm, which in turn was further confirmed by TEM micrographs. The optical band-gap of the host (3.92?eV) was calculated from the diffuse reflectance spectra. Moreover, the photoluminescence spectral studies showed that under near ultra-violet (NUV) excitation of 340?nm, our nanophosphor powder exhibits the characteristic emission peaks of trivalent samarium along with the emission of VO₄^3? (501?nm) group. The excitation energy transfer from vanadate group to Sm³⁺ produced a systematic color tunablity in white region itself. The optimum Sm³⁺ concentration for better luminescence was found to be 2?mol%. The critical distance for energy transfer was calculated to be 29.02?Å, which in turn assisted to shortlist the mechanism responsible for luminescence-quenching (dipole-dipole) arising from the over-doping of the activator. The photoluminescence decay curves revealed the decay kinetics of ⁴G_5/2 electronic state. Finally, the calculation of CIE color coordinates from emission spectra in MATLAB program unveiled a somewhat white-light emitter which may find potential applications in phosphor-converted white light emitting diodes (PC-WLED) under near-ultraviolet (NUV) excitation.     

Morphological,spectroscopic and photocatalytic properties of Eu3+:TiO2 synthesized by solid-state and hydrothermal-assisted sol-gel processes

Eu³⁺ doped TiO₂ powders were synthesized by solid-state reaction and hydrothermal-assisted sol-gel process. They were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence techniques. Both synthetic procedures yield the pure anatase phase of titania. The excitation and emission spectra and the decay profiles were measured for different thermal treatments of the samples, in order to investigate the effects of the synthesis conditions on the doping mechanism. The photocatalytic activity was investigated by measuring the degradation of methylene blue under UV light irradiation and a correlation between its efficiency and the luminescence performance has been proposed.     

Sol-gel synthesis and luminescence properties of Ba2SiO4:Sm3+ nanostructured phosphors

Ba₂SiO₄:Sm³⁺ nanostructure phosphors have been synthesized by a simple sol-gel method. Phase evaluation, structural characteristics and photoluminescence properties of the synthesized Ba₂SiO₄:Sm³⁺ powders were studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). X-ray diffraction results showed that all synthesized samples were single-phase barium silicate (Ba₂SiO₄) and samarium (Sm) ions were incorporated into the lattice of Ba₂SiO₄. Adding samarium to barium silicate changed the microstructure from vermicular to spherical structures. The Photoluminescence spectrum of Ba₂SiO₄:Sm³⁺ phosphors exhibited characteristic emission peaks at 562?nm which is due to the ⁴G_{5/2 →}⁶H_7/2 transition of samarium ions and corresponds to the orange region. The results showed that the barium silicate activated with 0.08?mol samarium exhibited the highest PL intensity.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

MgNb2O6:Dy3+ nanophosphor: A facile preparation,down conversion photoluminescence and UV driven photocatalytic properties

Series of (1–9 mol %) dysprosium (Dy³⁺) ions doped MgNb₂O₆ (MNO) nanophosphors were synthesized by chemical combustion process and their photo luminescent and photocatalytic behaviours were examined. Powder X-ray diffraction (PXRD) reveals the columbite structure and crystal structure parameters were calculated. The average crystallite size was found to be in the range of 20–30 nm as calculated by Scherrer's method. The photoluminescence (PL) of MgNb₂O₆:Dy³⁺ (λ_exc-393 nm) reflects white emission for the prepared samples as confirmed by CIE and CCT. The photocatalytic activities of these nanophosphors were probed for the decolorization of acid red 88 (AR-88) under UV light irradiation. The photocatalyst with MgNb₂O₆:Dy³⁺ (5 mol %) showed enhanced activity of 97%, attributed to effective separation of charge carriers. All the above experimental results confirm that, the optimized phosphor is quite useful for WLEDs, solid-state lighting applications and as a photocatalyst.     

红色荧光粉CaWO4:Eu3+,Gd3+的合成及其发光性能的研究

利用高温固相法合成了CaWO4:Eu3+,Gd3+红色荧光粉,通过X射线衍射、X射线光电子能谱和荧光光谱等对该荧光粉进行了表征。结果表明,CaWO4:Eu3+,Gd3+的荧光强度明显高于CaWO4:Eu3+,钆离子的最佳掺杂量为0.04。同时说明了钆离子引入到CaWO4:Eu3+中对其发光性能影响的机理以及不同浓度的钆对发光强度的影响。     

Synthesis of Bi2O3/TiO2 nanostructured films for photocatalytic applications

Dendritic growth of bismuth oxide nanostructured films was accomplished by reactive magnetron sputtering. The deposition of the Bi₂O₃ template layers was adapted to abide a vapour-liquid-solid mechanism in order to develop a 3D growth morphology with high surface area templates for photocatalytic applications. TiO₂ photocatalytic thin films were deposited at a later stage onto Bi₂O₃ layers. The obtained heterostructured films were characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy. Additionally, the photocatalytic efficiency was assessed by conducting an assay using methylene blue dye as testing pollutant under a UV-A illumination. The photocatalytic tests revealed that the Bi₂O₃ layers functionalized with TiO₂ thin films are more efficient at degrading the pollutant, by a factor of 6, when compared with the individual layered films.     

光照对Sr4Al14O25：Eu^2＋，Dy^3＋／TiO2-xNx复合材料光催化性能的影响

采用溶胶-凝胶法制备出Sr4Al14O25：Eu^2＋,Dy^3＋／TiO2-xNx复合材料。该复合材料对甲基橙具有较高的光催化效果,复合材料经紫外激发后,其光催化效果高于没有经紫外激发的复合材料的光催化效果,而且明显高于Sr4Al14O25：Eu^2＋,Dy^3＋／TiO2-xNx光照激发后光催化效率之和,同时讨论了Sr4Al14O25：Eu^2＋,Dy^3＋／TiO2-xNx复合材料的光催化机理。     

Synthesis and photoluminescent properties of high-efficient color-tunable Ba3Y2B6O15: Ce3+, Tb3+ phosphors

High-efficient Ce³⁺/Tb³⁺ co-doped Ba₃Y₂B₆O₁₅ phosphors with multi color-emitting were firstly prepared, and their structural and luminescent properties were studied by XRD Rietveld refinement, emission/excitation spectra, fluorescence lifetimes as well as temperature-variable emission spectra. Upon 365?nm excitation, the characteristic blue Ce³⁺ band along with green Tb³⁺ peaks were simultaneously found in the emission spectra. Moreover, by increasing concentration of Tb³⁺, a blue-to-green tunable emitting color could be realized by effective Ce³⁺→Tb³⁺ energy transfer. Furthermore, all Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ phosphors exhibit high internal quantum efficiency of ~?90%, while the temperature-variable emission spectra reveal that the phosphors possess impressive color stability as well as good thermal stability (T₅₀ =?~?120?°C). The results indicate that these efficient color-tuning Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ might be candidate as converted phosphor for UV-excited light-emitting diodes.     

Controllable synthesis of bifunctional material Ca2Ti2O6:Eu3+ and its comparative study on luminescence and photocatalytic properties with CaTiO3:Eu3+

Pure pyrochlore Ca₂Ti₂O₆, perovskite CaTiO₃, and their mixed crystalline phases with different proportions were controllably synthesized via a solvothermal method, followed by a subsequent calcination process. RIR (reference intensity ratio) data of Ca₂Ti₂O₆ were first obtained by X-ray diffraction (XRD), which can be used to quantitatively analyze the phase composition. When Eu³⁺ is doped into these calcium titanium oxides, they can be used as luminescent and photocatalytic materials. The structure, luminescence, and photocatalytic properties of pure pyrochlore Ca₂Ti₂O₆:Eu³⁺ and perovskite CaTiO₃:Eu³⁺ were comparatively studied in detail. The relative intensities of the excitation peaks and the emission peaks in Ca₂Ti₂O₆:Eu³⁺ and CaTiO₃:Eu³⁺ are different, which is attributed to the different symmetries of Eu³⁺ inhabiting the two kinds of lattices. In addition, although the luminescence intensity of CaTiO₃:3%Eu³⁺ is higher than that of Ca₂Ti₂O₆:3%Eu³⁺ under excitation at 394 nm, the luminescence intensity of Ca₂Ti₂O₆:3%Eu³⁺ is superior to that of CaTiO₃:3%Eu³⁺ under excitation at 464 nm and 533 nm. Photocatalytic experiments show that Ca₂Ti₂O₆:3%Eu³⁺ has better photocatalytic performance than CaTiO₃:3%Eu³⁺, which is mainly due to its smaller crystallite size, higher specific surface area and pyrochlore structure. In addition, biphase (Ca₂Ti₂O₆–CaTiO₃):3%Eu³⁺ has the best photocatalytic activity compared with the single phase Ca₂Ti₂O₆:3%Eu³⁺ and CaTiO₃:3%Eu³⁺, owing to the presence of heterojunctions that significantly reduced the band gap. It is anticipated that the discovery of this bifunctional Ca₂Ti₂O₆:Eu³⁺ would expand the application of rare earth-doped calcium titanium oxide materials.     

Synthesis, characterization and photocatalytic properties of sol-gel TiO2 films

The application of heterogeneous photocatalysis is described as an advanced oxidation process (AOP) for the degradation of the diazo reactive dye using immobilized TiO₂ as a photocatalyst. Starting TiO₂ solutions were prepared with and without the addition of polyethylene glycol (PEG) and TiO₂ films were directly deposited on a borosilicate glass substrate using the sol-gel dip-coating method. The surface morphology and the nanoscale roughness of TiO₂ films were studied by means of atomic force microscopy (AFM). Structural properties of TiO₂ were identified by X-ray diffraction (XRD). The decomposition behaviour of organic compounds from the gels was investigated using thermal gravimetry (TG) and differential scanning calorimetry (DSC). Photocatalytic activities of TiO₂ films in the process of degradation of the commercial diazo textile dye Congo red (CR), used as a model pollutant, were monitored by means of UV/vis spectrophotometry. The kinetics of the degradation of the CR dye was described with the Langmuir-Hinshelwood (L-H) kinetic model.The addition of PEG to the TiO₂ solution resulted in the changes in the film surface morphology, and affected the ratio of anatase-rutile crystal phases and the photocatalytic activity of TiO₂. The TiO₂ film prepared with PEG is characterized by higher roughness parameters (R_a, R_max, R_q, R_z and Z_max), a lower amount of the rutile phase of TiO₂, a higher amount of the anatase phase of TiO₂ and a better photocatalytic activity compared to the TiO₂ film without the addition of PEG.     

LiCa3MgV3O12:Sm3+: A new high-efficiency white-emitting phosphor

A novel single-phased white-light-emitting phosphor Sm³⁺ doped LiCa₃MgV₃O₁₂ (LCMV) was developed. The LCMV host was one self-activated bluish-green emitting phosphor, which possessed an efficient excitation band in the 250–400?nm wavelength range and showed an intense broadband bluish-green emission with internal quantum efficiency (IQE) of 39%. Doping Sm³⁺ ions in to LCMV host induced tunable-color emissions, due to the energy transfer from [VO₄]^3? to Sm³⁺ ions. Importantly, under 340?nm excitation, the LCMV:Sm³⁺ can emitted bright white light by combining the self-activated luminescence of LCMV host and the red emissions of Sm³⁺ ions, and the IQE of the white-emitting composition-optimized LCMV:0.01Sm³⁺ phosphors reached up to 45%. These white-emitting LCMV:Sm³⁺ phosphors have potential applications in white light-emitting diodes and optical display devices.     

Facile Synthesis of Amine-Functionalized Eu3+-Doped La(OH)3 Nanophosphors for Bioimaging

Here, we report a straightforward synthesis process to produce colloidal Eu³⁺-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent surface modification. The La(OH)₃:Eu³⁺ NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission peaks at 597 and 615 nm (λ_ex = 280 nm). The red emission, due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)₃:Eu³⁺ NPs possess the potential to serve as a luminescent bioimaging probe.     

Modification of Optical Properties of SrAl_2O_4：Eu~（2＋）,Dy~（3＋） Phosphor by Terbium Doping

以尿素为燃料,采用快速燃烧法在650℃合成了Tb3＋掺杂的SrAl2O4：Eu2＋,Dy3＋新型长余辉光致发光材料。研究了Tb3＋掺杂对Eu2＋,Dy3＋共激活的铝酸盐长余辉发光材料的发光特性的影响。X射线衍射分析结果表明：当Tb3＋的掺杂量x=0.17%时,合成的样品结构为单相SrAl2O4单斜晶系。光致发光测试结果表明：样品的激发光谱为峰值位于345nm附近的连续宽带谱,发射光谱为峰值位于510nm左右的连续宽带谱。余辉衰减曲线结果表明：Tb3＋的适量掺杂可以提高铝酸锶的余辉性能。与SrAl2O4：Eu2＋,Dy3＋相比,掺杂Tb3＋有利于形成结晶度良好的固溶体,样品中的晶体细密紧凑,颗粒粒径约为100nm。     

Enhanced green upconversion luminescence properties of Er3+/Yb3+ co-doped strontium gadolinium silicate oxyapatite phosphor

Upconversion Sr₂(Gd_.98-xEr_.02Yb_x)₈Si₆O₂₆ (SGSO:2Er³⁺/xYb³⁺) phosphor materials were synthesized using a citrate sol-gel process. X-ray diffraction patterns confirmed their hexagonal structure. Field emission scanning electron microscopy images of SGSO:2Er³⁺/xYb³⁺ phosphors depicted submicron particles. The enhanced upconversion luminescence properties of SGSO:2Er³⁺/xYb³⁺ phosphors were analysed as a function of Yb³⁺ ion concentration and laser power. The energy transfer induced enhanced emission of the Er³⁺/ Yb³⁺ ions co-doped SGSO phosphors was ascribed to multi-phonon relaxation. The calculated chromaticity coordinates of the SGSO:2Er³⁺/xYb³⁺ phosphors showed emissions could be tuned by changing Yb³⁺ ion concentration. Optimized sample exhibited the chromaticity coordinate values near to the ultra-high definition television standard green emission coordinates.     

Thermally stable double perovskite CaLaMgSbO6:Eu3+ phosphors as a tunable LED-phosphor material

A series of Eu³⁺ ions activated double perovskite CaLaMgSbO₆ phosphors were successfully synthesized. Crystal structure was investigated by XRD and the results showed that this double perovskite exhibited rock-salt ordering of B-site ions. High-resolution transmission electron microscopy was used to prove the existence of B-site ordering. Thereafter, luminescence properties of the as-prepared powders were discussed in detail. The phosphors could be well excited by ultraviolet, near ultraviolet, and blue light. The quenching concentration for the transition of ⁵D₀-⁷F₂ reached up to 50.0 mol%. The theoretical quenching concentration and quenching mechanism were discussed in detail. Excellent thermal stability of this double perovskite phosphor was obtained and the quenching mechanism was investigated based on the configurational coordinate diagram. The CIE coordinates showed that this double perovskite phosphor had great potential in solid state lighting.     

Photoluminescence properties of Pr3+ ion-doped YInGe2O7 phosphor under an ultraviolet irradiation

Pr³⁺ ion-doped YinGe₂O₇ phosphors are synthesized by a vibrating milled solid state reaction. There is a red shift for the excitation peak for the charge transfer transition between In³⁺ and O^2- ion because the numbers of oxygen vacancies change the structure, which leads to a change in the crystal field. The results indicate that the emission spectra for the YinGe₂O₇:Pr samples under an excitation of 263 nm exhibit two dominant peaks at 486 and 604 nm, which are respectively assigned to the ³P₀→³H₄ and ¹D₂→³H₄ transitions. The chromaticity coordinate for (Y_1?xPr_x)InGe₂O₇ phosphors varies with the Pr³⁺ doping concentration, from white, to greenish, to blueish. This has a potential application as a white light emitting phosphor for ultraviolet light-emitting diodes.     

Photoluminescence properties of NUV light excited Ba(Mg1/3Nb2/3)O3:Eu3+ red phosphor with high color purity

In this work, a new red phosphor with high color purity, Eu³⁺ ions doped Ba(Mg_1/3Nb_2/3)O₃ phosphor has been prepared by wet chemical method. The structure analysis suggests BMN:x%Eu phosphors have a hexagonal phase and Ba²⁺ ions are replaced by Eu³⁺ ions in BMN. Upon excitation of NUV light, the BMN:x%Eu phosphors emit strong red light around 615?nm, derived from the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The relationship between luminescent properties and structure of BMN:x%Eu was discussed. The Judd-Ofelt intensity parameters (Ω₂, Ω₄) were calculated to analyze the asymmetry of the Eu³⁺ ions site occupancy further, and the quantum efficiency of BMN:3%Eu was found to be 77.26%. In addition, the decay curve indicates the decay time(τ) of BMN:3%Eu is determined to be 1.34?ms and Eu³⁺ ions occupy only one type of site. The CIE chromaticity coordinate (0.656,0.344) of BMN:3%Eu is quite close to the red phosphors standard value (0.670, 0.330), which indicates BMN:x%Eu can be a suitable red phosphor used in NUV-based white LEDs.     

Protective properties of SiO2 with SiO2 and Al2O3 nanoparticles sol-gel coatings deposited on FeCrAl alloys

Five layer SiO₂ coatings containing SiO₂ or Al₂O₃ nanopowders were deposited on FeCrAl alloy support by sol-gel method. Studies of protective properties of the coatings were carried out during high temperature cyclic oxidation. Changes in surface topography, structure and chemical composition of the surface layer of FeCrAl alloy were investigated. It has been shown that the type of nanofillers present in the SiO₂ coating (about 2.5?wt%) affects morphology of Al₂O₃ growing scale and determines the heat resistance of FeCrAl alloy. The lowest relative mass change (approx. 1.3%) after 10 oxidation cycles in air at 900?°C (one cycle = 12?h) was measured for the samples with coatings containing hydrophilic nanosilica (Aerosil 380) as filler. The protective efficiency of the coatings in the process of high-temperature oxidation is from 66% to 85%. The thickness of the formed scale and the value of the parabolic rate constant depend on the type of nanopowder in the coating.     

Characterization and tribological investigation of sol-gel Al2O3 and doped Al2O3 films

Thin films of Al₂O₃ and doped Al₂O₃ were prepared on a glass substrate by dip coating process from specially formulated ethanol sols. The morphologies of the unworn and worn surfaces of the films were observed with atomic force microscope (AFM) and scanning electron microscope (SEM). The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of obtained thin films sliding against Si₃N₄ ball were evaluated and compared with glass slide on a one-way reciprocating friction tester. XPS results confirm that the target films were obtained successfully. The doped elements distribute in the film evenly and exist in different kinds of forms, such as oxide and silicate. AFM results show that the addition of the doped elements changes the structure of the Al₂O₃ films, i.e., a rougher and smoother surface is obtained. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. As the results, the doped films exhibit better tribological properties due to the improved toughness. Sever brittle fracture is avoided in the doped films. The wear of glass is characteristic of brittle fracture and severe abrasion. The wear of Al₂O₃ is characteristic of brittle fracture and delamination. And the wear of doped Al₂O₃ is characteristic of micro-fracture, deformation and slight abrasive wear. The introduction of ZnO is recommended to improve the tribological property of Al₂O₃ film.