High-temperature Solid-phase Method Research Articles

Effects of liquid-phase carbon combining surfactant coatings on the performance of LiMn0.2Fe0.8PO4 cathode materials

Efforts to reduce the particle size of LiFexMn1-xPO4 materials and apply conductive carbon coatings have yielded substantial benefits in terms of obtaining lithium-ion batteries (LIBs) with enhanced electrochemical performance. However, LiFexMn1-xPO4 materials with small particle sizes and uniform carbon layers cannot be obtained by the conventional high-temperature solid-phase method, which is the most convenient and applicable method for the industrial-scale preparation of the cathode materials used in commercial LIBs. The present work addresses this issue by applying the cationic surfactant cetyltrimethylammonium bromide (CTAB) in conjunction with LiMn0.2Fe0.8PO4 (LMFP) particles, and obtaining a carbon layer by replacing the conventional in-situ solid-phase carbon coating process with a secondary liquid-phase coating process using sucrose as the carbon source. The CTAB surfactant is observed to be uniformly adsorbed on the surface of LMFP particles, and maintains small LMFP particle sizes by operating as a dispersant preventing their agglomeration. Additionally, the carbon network formed by CTAB pyrolysis acts as an intermediate medium ensuring that the conductive carbon layer is uniformly and firmly adhered to the LMFP particle surfaces at a high preparation temperature of 680°C. This composite carbon layer is demonstrated to enhance lithium-ion transport, while concurrently acting as a barrier interfering with manganese diffusion within the electrolyte during charge-discharge cycling. As a result, the optimal LMFP-based cathode material achieves reversible specific capacities of 160 mAh g−1 and 120 mAh g−1 at charge-discharge rates of 0.1 C and 5 C, respectively, and the capacity retention is 88 % after 500 cycles at 1 C. Hence, the results verify that the proposed surfactant-mediated liquid-phase carbon coating process is an effective method for enhancing the overall electrochemical performance of LMFP-based cathode materials.

Cr3+ and Ni2+ Co-doped near-infrared dual-emission garnet phosphor for spectroscopic applications

Near infrared spectroscopy is a simple, fast, and non-invasive technique for detecting the composition of substances. However, most NIR phosphors cannot cover the near-infrared I and II regions, which limits the types of substances that can be detected. Herein, Cr3+, Ni2+ co-activated NIR Y3Al2Ga3O12(YAGG) garnet phosphors were synthesized via high-temperature solid-phase method. Due to the energy transfer from Cr3+ to Ni2+, the emission spectra of YAGG: Cr3+, Ni2+ are composed of NIR I emission of Cr3+ at 710 nm and NIR II emission of Ni2+ at 1420 nm. The measured internal and external quantum efficiencies of YAGG: 0.08Cr3+, 0.005Ni2+ under 450 nm excitation are 54.4 %, and 26.7 %, respectively. This sample was selected to fabricate pc-LEDs, and fill the emission spectrum gap with Mg2GeO4: 0.01Cr3+. The pc-LED fabricated with PiG film do not exhibit strong characteristic absorption in NIR II region, significantly reduce the re-absorption and thermal quenching of the phosphors. The electro-optical conversion efficiency of PiG pc-LED reaches 6.49 % at 10 mA; The results indicate that YAGG: Cr3+, Ni2+ and the fabricated NIR pc-LED are good near-infrared substance detection light source scheme.

A samarium (Ⅲ)-activated tantalum-based double perovskite phosphor with high thermostability

Inorganic double perovskite phosphor materials have received much attention in solid-state lighting domain due to efficient and versatile luminescence colors. This study employs a high-temperature solid-phase method to synthesize a series of Sm3+-activated Sr2YTaO6 (SYTO):Sm3+ phosphors with double perovskite structure. The structure, morphology, and content/temperature-dependent orange-red emissions are thoroughly elucidated. For SYTO:3 mol%Sm3+, the luminescence intensity at 423 K remains 95 % of that at 298 K, verifying high thermostability. Meanwhile, the phosphor exhibits good resistance to color shifting. A high Sm3+ content induces luminescence quenching due to dipole–dipole interaction. Finally, the synthesized material is utilized to fabricate a satisfactory and warm white light-emitting diode.

Study on the novel green magnetoplumbite-type oxide BaZn6-xNixTi6O19: synthesis, structure and properties

Magnetoplumbite-type oxides display various properties and find applications in multiple fields. In this study, a novel magnetoplumbite-type solid solution BaZn6-xNixTi6O19 (0 ≤ x ≤ 4) with vivid green color was synthesized through a high-temperature solid-phase method for the first time. The as-synthesized BaZn6-xNixTi6O19 solid solution crystallizes in the space group of P63/mmc. The solid solution exhibits excellent green property, and its color is adjustable with increasing doping levels of Ni2+. The depth of color originates from the content and position of Ni2+ in the solid solution. BaZn6-xNixTi6O19 is suitable for PMMA (Polymethyl methacrylate) pigment and hydrophobic coating. Colored PMMA containing BaZn6-xNixTi6O19 exhibits vibrant colors with high saturation, showing excellent application potential. The hydrophobic coating compounded with BaZn6-xNixTi6O19 exhibits near-superhydrophobic properties and demonstrates excellent self-cleaning effects under simulated natural environmental conditions.

Enhanced luminescence performance in double perovskite CaSrLaSbO6: Mn4+ red emission phosphors for indoor plant growth via cation doping

Novel CaSrLaSbO6: Mn4+ red-emitting phosphors with double perovskite structure were successfully synthesized by the high-temperature solid-phase method. CaSrLaSbO6:Mn4+ phosphor showed a broad excitation band with different excitation peaks from 250 nm to 600 nm owing to the Mn4+-O2- charge transfer and 4A2g → (4T1g, 2T2g, and 4T2g) transitions of Mn4+ ions and exhibited intense deep-red emission at 678 nm attributed to the 2Eg → 4A2g transition of Mn4+ ions. To further enhance the performance of the phosphor, a cation doping method was adopted in this paper to synthesize CaSrLa1-xLnxSbO6: Mn4+ (Ln = Gd, Y) phosphors. The luminescence intensity of the samples was enhanced after doping with different cations, and the related mechanism was discussed. In addition, the microstructure and crystal field environment were systematically investigated. The luminescence intensity of the CaSrLa0.85Y0.15SbO6: Mn4+ phosphor was about 1.82 times higher than that of CaSrLaSbO6: Mn4+phosphor. The emission spectrum of the sample matched well with the absorption band of plant pigments. Furthermore, the plant growth LEDs and light-conversion film were prepared by using the optimized CaSrLa0.85Y0.15SbO6: Mn4+. The results indicate that the designed phosphors have great potential applications in agricultural cultivation.

A new red phosphor for high time-resolved thermal sensitivity and plant growth.

Luminous materials with a rapid lifetime response have garnered significant interest in sensing technology. In this work, the transition element Mn doped phosphor Sr2TiO4:Mn4+ was synthesized by a traditional high temperature solid phase method. The emission peak of Sr2TiO4:0.009Mn4+ aligns closely with the absorption peak of phytochrome Pfr. The temperature-dependent photoluminescence (PL) spectra and lifetime of Sr2TiO4:0.009Mn4+ were examined within the temperature range of 273-323 K. The temperature sensing characteristics based on the lifetime were analyzed, and the maximum relative sensitivity was 14.93% K-1 at 309 K. The high sensitivity of the Sr2TiO4:0.009Mn4+ phosphor makes it a promising material for temperature sensing applications.

Tuning β-Si3Al3O3N5 phosphors by Eu or Ce doping for white light-emitting diodes (wLEDs)

SiAlON-based phosphors have garnered considerable attention in the field of white lighting owing to their excellent thermal stability, and rare earth doped SiAlON-based phosphors are expected to be used in a new generation of lighting sources. In this work, Eu2+ or Ce3+ doped Si3Al3O3N5 phosphors were synthesized by high temperature solid phase method. The microstructure of the phosphors exhibited irregular grain. The two phosphors exhibit green and cyan luminescence under 365 nm excitation, which are derived from the 5d-4f transitions of Eu2+ and Ce3+, respectively. The quenching concentrations are 3 % and 4 % for Eu2+ and Ce3+doped phosphors, respectively. The fluorescence intensity of Eu2+ and Ce3+ activated SiAlON powders decreased to 50 % of the room temperature intensity at 179 °C and 170 °C, respectively. The thermal activation energy values of the two phosphors were 0.35 eV, and the coordinate configuration diagram was constructed to comprehensively analyze the thermal quenching behavior of phosphors. Finally, the two phosphors powders were mixed with red and blue fluorophore to obtain white LEDs, showing low color temperature, high color rendering, high power unsaturation and long half-life. The SiAlON-based phosphors with excellent thermal stability obtained in this work achieve different wavelengths of luminescence in the green region. The results show that the β-Si3Al3O3N5 phosphor can be used as a candidate material for high-quality green light supplement for wLEDs.

The synthesis and application of Ni2+-doped NIR-II Phosphors composed of MgAl2-xGaxO4 solid-solution

Near-infrared (NIR) light has been widely used in fields, such as biometrics recognition, security monitoring, lighting for indoor agriculture, food safety inspection and biomedical imaging. NIR phosphors are crucial components for NIR phosphor-conversion light-emitting diodes (NIR pc-LED). Compared with the traditional high-temperature solid phase method for spinel-type phosphors, the synthesis by the sol-gel combustion method is rapid, more efficient, and requires lower temperatures, with good homogeneity and uniformed nano-size particle. Here we report the synthesis of a panel of NIR phosphors that are composed of nano-sized Ni2+-doped MgAl2-xGaxO4 solid-solution of spinal crystals with high phase purity. By adjusting the ratios of Al/Ga, the Ni2+-doped phosphors with spinel (MgAl2O4) to hybrid-spinel (MgGa2O4) crystal structures were obtained. The phosphor with the Al/Ga ratio of 0.8–1.2 showed the maximal NIR emission intensity, which was 5.9 times higher than that of the MgAl2O4 spinel structure, with an internal photoluminescence quantum efficiency of 31.63 %. The phase transformation of the crystal form from spinel to hybrid-spinel resulted in a shift of the emission peak from 1223 nm to 1287 nm, realizing a ∼ 64 nm structure-dependent tunability of NIR luminescence. We assembled a NIR pc-LED device using the optimal phosphor and a commercially available near ultraviolet LED, and experimentally demonstrated its application for night-vision monitoring and bioimaging of veins in a human hand.

Co-doping induced Mn-vacancy LiMn2O4 based membrane electrode for lithium extraction by electrochemically switched ion permselective process

LiMn2O4 (LMO) is considered an effective electroactive material for electrochemical lithium extraction from aqueous solutions. However, the stability issue limits its practical application. Herein, Co-doping induced Mn-vacancy LiMn2O4 (LCMO) powders were synthesized by a high-temperature solid-phase method, which were further applied to prepare an electrochemical permselective membrane electrode for selective lithium-ion extraction. Physicochemical characterizations combining with density functional theory (DFT) calculations revealed that Co-doping at 8a site will induce the formation of Mn vacancies in LMO, which can reduce the content of easily dissolutive trivalent Mn (Mn3+) and lower the Li+ migration energy barrier. As a result, the Li+ permeation flux of optimized LCMO-0.04 (Co: Mn = 0.04: 1.96) based membrane electrode (156.809 mmol·m−2·h−1) was increased by 85.65 % compared to that of LMO-based one (84.461 mmol·m−2·h−1) in an electrochemically switched ion permselective (ESIP) system. The selectivity factors of Li+/ Na+, Li+/Mg2+, Li+/ K+ for the LCMO-0.04 based membrane electrode were up to 10.06, 11.69, and 15.19, which were about twice as high as those for LMO membrane based one. After 1000 circles of cyclic voltammetry (CV) tests, the CV area of the LCMO-0.04 based membrane electrode maintained 91.59 % of the initial value, demonstrating remarkable electrochemical stability.

Up-conversion luminescence and temperature sensing properties of Ho3+-, Tm3+-, and Yb3+-codoped Bi2WO6 materials in a water environment

A series of x%Ho3+, 5 %Tm3+, y%Yb3+:Bi2WO6 (x = 0, 0.5, 1, 3, 5; y = 0.5, 1, 3) luminescent materials was prepared using a high-temperature solid-phase method. The microstructure, up-conversion luminescence, and temperature sensing properties of the synthesized powders were analyzed. X-ray diffraction patterns revealed that doping with Ho3+, Tm3+, and Yb3+ ions at certain concentrations did not affect the orthorhombic crystal structure of the Bi2WO6 host. Scanning electron microscopy revealed that the morphology of the sample consisted of lumpy particles with a particle size range of 1–5 µm and agglomeration. SEM mapping and energy-dispersive X-ray spectroscopy analyses revealed that each element was relatively uniformly distributed on the particle surface. Under 980 nm excitation (380 mW), the strongest luminescence of the sample was obtained when both Ho3+ and Yb3+ doping concentrations were 1 %. Compared with the luminescence of the 5 %Tm3+ and 1 %Yb3+:Bi2WO6 sample, with increasing Ho3+ concentrations, the luminescence intensity of Tm3+ was first enhanced and subsequently weakened, whereas the luminescence of Ho3+ was significantly weakened, which indicates the positive energy transfer from Ho3+ → Tm3+. At 980 nm (80–380 mW), for the 1 %Ho3+, 5 %Tm3+, and 1 %Yb3+:Bi2WO6 sample, the 538 nm, 545 nm, 660 nm, and 804 nm emission peaks originated from the two-photon absorption. FIR660 nm/804 nm, FIR545 nm/804 nm, and FIR538 nm/804 nm were used to characterize the temperature and corresponded to temperature sensitivities Sr of 0.0046 K−1, 0.022 K−1 and 0.024 K−1 at 573 K, respectively. At 498 K, the minimum temperature resolution δT values were 0.03384 K, 0.03203 K and 0.04373 K. When the temperature increased from 298 K to 573 K, the powder sample luminescence gradually shifted from the yellow-green region to the red region. The results of environmental discoloration and thermochromic performance tests indicate that this sample has potential application in optical anti-counterfeiting. FIR804 nm /660 nm and FIR804 nm /538 nm were obtained for the 40 NTU turbidity suspension under identical excitation conditions. At 298 K, for the 40 NTU turbidity sample, the maximum Sr values were 0.0197 K−1 and 0.0405 K−1; at 340 K, the minimum temperature resolutions δT values were 0.54037 K and 0.66237 K. When the temperature decreased from 340 K to 298 K, the luminescence of the 40 NTU suspension samples gradually shifted from the yellow region to the green region.

Preparation of highly hydrophilic cesium ion sieve and its performance in adsorbing Cs+

The unique properties of cesium compounds have garnered increasing attention, among which Cs2Ti6O13 shows great potential for applications. This paper synthesized Cs2Ti6O13(CTO-3) using a template-assisted solvothermal method with cesium carbonate as the cesium source and tetrabutyl titanate as the titanium source. Among them, F127 and hexadecylamine are used as template agents to modulate the surface morphology and hydrophilicity of the precursor. The cesium ion sieve H2Ti6O13 (HTO-3) synthesized after hydrochloric acid pickling has a large specific surface area and good hydrophilicity. This structure is conducive to the ion exchange between Cs+ and H+, resulting in a fast adsorption rate. It is completed within 2 h, and the adsorption capacity reaches 360 mg/g, which is significantly greater than that of the traditional high-temperature solid-phase method. The adsorption process of Cs+ on HTO-3 is more consistent with the pseudo-second-order kinetic equation model, and the adsorption process is chemical adsorption. HTO-3 exhibited good selectivity and cycle stability. At the fifth time of the adsorption-resolution cycle, the adsorption capacity was 87.1 % of the first time.

Novel self-activated red-emitting CsSrEu (PO3)6 phosphor: Synthesis, luminescent properties and enhancement by partially anion substitution

Novel self-activated red-emitting CsSrEu(PO3)6 was synthesized by high-temperature solid-phase method, and their enhanced luminescence were obtained by the modification of local structure. CsSrEu(PO3)6 was efficiently excited at 394 nm and emitted bright red light centered around 609 nm. Their luminescence intensity of CsSrEu(PO3)6 phosphor substituted by (BO3)3-/(SiO4)4- is about 1.346 or 1.454 times of the initial values respectively. The temperature-dependent luminescent spectra show that the emission intensity of CsSrEu(PO3)6 substituted by (BO3)3-/(SiO4)4- at 423 K remains 90.9 % and 86.6 % of the initial value respectively. The internal quantum efficiency is 88.4 % and 83.5 % respectively. White light-emitting diode fabricated by the phosphors, commercial blue-green phosphors and 395 nm chips show high color quality. The overall results indicate that the CsSrEu(PO3)6 phosphor substituted by (BO3)3-/(SiO4)4- group is promising candidate in warm white LED and anionic group substitution can be used to optimize luminescent properties of phosphors.

Thermally enhanced luminescence and photoluminescence properties of green-emitting Lu2(1-x)Tb2x(WO4)3 phosphors

A series of Lu2(1-x)Tb2x(WO4)3 (x = 0.00–1.00) white powder materials were prepared by a high-temperature solid-phase method. The crystal structure, microscopic morphology, elemental composition, bandgap energy, photoluminescence properties, and thermal stability of luminescence of the prepared materials were analyzed and studied through room and high temperature X-ray diffraction patterns, field emission scanning electron microscopy images, energy energy-dispersive spectra and X-ray photoelectron spectra, diffuse reflectance spectra, room and high temperature photoluminescence spectra. Under 260 nm excitation, the green emitting Lu2(1-x)Tb2x(WO4)3 samples exhibited an optimum Tb3+ doping concentration at x = 0.30. Calculated results illustrate that the concentration quenching was mainly caused by dipole-dipole interaction. Lu1.98Tb0.02(WO4)3 phosphor exhibited thermally enhanced luminescence at 120 °C, with a maximum luminescence intensity of 254 % of the initial room temperature intensity. Lu1.4Tb0.6(WO4)3 phosphor exhibited thermally enhanced luminescence at 150 °C, with a maximum luminescence intensity of 109 % of the initial room temperature intensity. The mechanism of the thermally enhanced luminescence phenomenon is further discussed to be the adsorbed crystal water and the negative thermal expansion of the material. Thermally enhanced luminescence is of great significance in overcoming luminescent thermal quenching phenomenon, improving the luminescence efficiency, optimizing the material design, and so forth. It has potential applications in high-temperature lighting, display technology, temperature sensing, and optical anti-counterfeiting.

NIR-II luminescence and temperature sensing properties based on double perovskite La2MgTiO6: Yb3+/Er3+/Ho3+ phosphor

The near-infrared-II (NIR-II) fluorescence thermometer based on rare earth-doped double perovskite is rarely. Herein, Er3+-Ho3+ and Yb3+ co-doped lead-free double perovskite La2MgTiO6 (LMTO) phosphors were synthesized by a conventional high temperature solid phase method. The phase purity and morphology of the samples were analyzed using XRD and FE-SEM. The NIR-II luminescence properties of LMTO: Er3+-Ho3+-Yb3+ phosphors were systematically investigated under laser irradiation at 980 nm. A NIR-II fluorescence thermometer was also designed based on non-thermal coupled energy levels originated from the 4I13/2 energy level of Er3+ and the 5I6 energy level of Ho3+. The maximum value of relative sensitivity (Sr) was 0.54 % at 513 K. Compared to visible thermometers (LMTO: Er3+-Yb3+ and LMTO: Ho3+-Yb3+), the NIR-II thermometers offer better temperature measurement capability and penetration depth. All the experimental results show that the NIR-II thermometer with a wider range and higher sensitivity has been realized, which puts forward a new idea for the design and optimization of NIR-II thermometers.

Study on structural luminescence characteristics of a new Dy3+ activated white luminescent phosphor

A series of Y1-xGa1.5Al1.5(BO3)4: xDy3+ were prepared by a high-temperature solid-phase method. Rietveld refinement characterized the phase purity of the samples obtained, suggesting that the prepared phosphors were high-purity material phases. After synthesizing high purity phase, the luminescence mechanism is revealed, under 348 nm excitation in Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor, the samples have two characteristic peaks at 480 nm and 572 nm and the burst mechanism is dipole-dipole mechanism. The mechanism of luminescence and quenching is analyzed by analyzing the band structure, and the relationship between the band gap and thermal stability is explained. The prepared phosphor has a quantum efficiency of 51.22 % and exhibits intense white light emission. The thermal stability of the samples was characterized, and the phosphor could still achieve 88.20 % thermal stability at 423 K. Finally, the chromaticity coordinates of the Y1-xGa1.5Al1.5(BO3)4: xDy3+ phosphors all fall in the white-light region, with the color coordinates around (0.33, 0.33). By combining with the 365 nm chip and Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor, the W-led device with Ra = 68.3 and CCT = 6670 K was synthesized. Therefore, the Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor prepared in this experiment has some application value in the field of solid-state lighting.

A novel multifunctional Eu3+/Mn4+ co-doping double perovskite phosphor for applications in LEDs and optical thermometry

In recent years, phosphors have played important roles in solid-state lighting, plant growth lighting and optical temperature measurement. In this work, novel La3Mg2NbO9:Eu3+,Mn4+ phosphors were successfully prepared by the high temperature solid phase method and innovative multimode applications were investigated in optical thermometry, plant growth and White-LEDs. The crystal structure, surface morphology, photoluminescence, temperature sensing properties and luminescence mechanism of La3Mg2NbO9:Eu3+,Mn4+ phosphors were investigated in detail. Benefiting from the different responses of Eu3+ and Mn4+ ions to temperature, the La3Mg2NbO9:0.06Eu3+,0.0095Mn4+ sample shows excellent optical thermometry performance in the range of 303 ∼ 478 K. The maximum values of relative sensitivity (Sr) reach 2.7 % K-1 (@478 K) according to the fluorescence intensity ratio method and the maximum of Sr is 5.2 % K−1 (@428 K) based on the fluorescence lifetime method. Furthermore, the electrochromic spectrum of the red pc-LED prepared using La3Mg2NbO9:0.06Eu3+,0.005Mn4+ phosphor perfectly overlapped with the absorption bands of the photosensitive pigments for planting, and another white pc-LED prepared using La3Mg2NbO9:0.06Eu3+,0.0025Mn4+ phosphor emitted bright white light with a color rendering index of 89.8, color coordinate of (0.3468, 0.3557) and correlated color temperature of 4945 K. All the results demonstrate that the La3Mg2NbO9:Eu3+,Mn4+phosphors are promising for the field of non-contact optical temperature thermometry, plant lighting lamps and pc-LED backlit displays.

The effect of trace Fe3+ on the magneto-optical properties of Tb3+ doped B2O3-GeO2-Al2O3-ZnO-BaO glass

Magnetic particles of BaFe12O19 were synthesized using a high-temperature solid-phase method. Magneto-optical glass samples were prepared by incorporating different concentrations of Fe3+ ions (ranging from 0 to 0.25 mol%) into the glass matrix with a constant doping of Tb2O3 (30 mol%) using a high-temperature melting method. The glasses are composed of B2O3-GeO2-Al2O3-ZnO-BaO-Tb2O3 (BGAZBa-T30-xFe). The effects of varying Fe3+ ion concentrations on the structure, physical properties, and magneto-optical performance of BGAZBa-T30 glass were investigated. The study reveals that the density and magneto-optical properties of the glass are enhanced with the increase of Fe3+ ion concentration. When the Fe3+ ion concentration reaches 0.20 mol%, the Verdet constant of BGAZBa-T30 glass increases from −82.51 rad/(T·m) to −91.90 rad/(T·m) at an incident light wavelength of 633 nm. Meanwhile, the density rises from 4.93 g/cm3 to 4.98 g/cm3. Notably, the BGAZBa-T30-0.20Fe glass sample exhibits excellent magneto-optical performance, with a Verdet constant value of −142.50 rad/(T⋅m) at an incident light wavelength of 515 nm, which is 1.2 times that of the glass matrix main body (−118.28 rad/(T·m)). This presents potential research value in the field of optoelectronic functionality.

Luminescence and Energy Transfer Properties of Color-Tunable Dy3+, Eu3+ co-Activated NaGdSiO4 Phosphor for WLED with Great Thermo-Stability.

A series of NaGd1-x-ySiO4: y Dy3+-x Eu3+ phosphors were synthesized by a high-temperature solid-phase method. The optimal doping ion concentration of Dy3+ ions for this phosphor was determined to be 1 % from the emission spectra. The energy transfer between Dy3+ and Eu3+ ions at 351 nm was investigated by photoluminescence spectra and fluorescence decay curves. At the excitation wavelengths of 275 nm, 351 nm, 366 nm, and 394 nm, a change from yellow to white to red light can be realized by adjusting the doping concentration of Eu/Dy ions. Particularly, by testing the temperature-dependent fluorescence spectrum of the phosphor, it can be found that the luminous intensity of the phosphor is as high as 96 % when 394 nm excitation is employed at 413 K. It was the maximum at this temperature comparing with other phosphors as far as we know. The color coordinate values show that the NaGd1-x-ySiO4:×Dy3+-y Eu3+ phosphors are very close to the white light color coordinates (x=0.33, y=0.33) under 351 nm excitation. Meanwhile, the correlated color temperature is between 5062-7104 K. These results indicate that this phosphor is a promising candidate for high-quality WLED.

Preparation and properties of cordierite-based multi-phase composite far-infrared emission ceramics by fine-grained tailings

In this paper, cordierite ceramics with high far-infrared emission properties are synthesized by a high-temperature solid-phase method using molybdenum tailings and vanadium-titanium magnetite tailings. The microstructure, physical properties and far-infrared emission mechanism of ceramics are investigated. The results show that the ceramics synthesized with 10 wt% molybdenum tailings and 30 wt% vanadium-titanium magnetite tailings have a flexural strength of 67 MPa, a bulk density of 2.531 g/cm3 and a maximum far-infrared emissivity of 0.958 when the sintering temperature is 1200 °C. The crystal phase of the ceramic are 21.4 % cordierite and 58.7 % magnesia-alumina spinel. In the sintering process, the Fe3+ in vanadium-titanium magnetite tailings doped into the cordierite to substitute the Mg2+, which has the similar ionic radius with Fe3+, to form a substitutional solute. Ionic substitution causes the lattice parameters of cordierite larger, reducing the symmetry of the lattice vibrations and leading to lattice distortion. In addition, the composition of a large amount of magnesia-aluminum spinel is attributed to the far-infrared emission properties of ceramics.

Effect of ion occupancy and Li+ ion doping on luminescence characteristics of CaLaGaO4:Bi3+ blue phosphor

In recent years, the application of Bi3+ ions doped luminescent materials in the field of optoelectronics has attracted wide attention. In this paper, CaLaGaO4:xBi3+(x = 0.005, 0.0075, 0.01, 0.0125, 0.015, 0.02, 0.025mol) blue phosphors were synthesized by high temperature solid phase method. The theoretical and experimental bandgap values after Bi3+ ions doping is reduced, indicate that electrons can be transferred from valence band to conduction band better after Bi3+ ions doping, which increases the carrier concentration and improves the luminous efficiency. In addition, due to the doping of Li+ ions under 365 nm excitation, the emission intensity is increased by 2.5 times, shows high brightness blue light, with excellent thermal stability (423K/303K = 83 %), quantum efficiency is 56 %, and CaLaGaO4:0.01Bi3+, 0.008Li+ phosphor was mixed with (Ba,Sr)2SiO4:Eu2+ commercial green phosphor and (Ca,Sr)AlSiN3:Eu2+ red phosphor in a certain proportion. The WLED combined with 365 nm chip has a high color rendering index Ra = 90.2. Relevant color temperature CCT = 5502K.