发光二极管用SrWO4:Eu3+红光荧光粉激发谱强度的调控

采用化学共沉淀法制备了Eu³⁺掺杂摩尔分数不同、煅烧温度不同的SrWO₄:Eu³⁺系列发光粉体, 所制备的粉体均具有Eu³⁺特征的强室温红光荧光发射. 通过调节煅烧温度和掺杂摩尔分数来调控近紫外和蓝光吸收强度, 进而调控用395 nm的近紫外光和465 nm的蓝光激发样品所得红光发光强度. 研究结果表明, 所制备的SrWO₄:Eu³⁺红光荧光粉可以被紫外和蓝光发光二极管有效激 关键词： 稀土掺杂 4:Eu³⁺')" href="#">SrWO₄:Eu³⁺ 光致发光 白光发光二极管     

Luminescent properties and the morphology of SrMoO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> powders synthesized <Emphasis Type="Italic">via</Emphasis> combining sol-gel and solid-state route

SrMoO₄:Eu³⁺ red phosphors were prepared by combining sol-gel and solid-state route. Citric acid and ethylenediaminetetraacetic acid (EDTA), employed as the chelating agents, were added to the aqueous solutions of metal nitrates. X-ray diffraction (XRD) and photoluminescent spectra techniques (PL) were used to characterize the resultant powders. The results indicated the obtained SrMoO₄:Eu³⁺ phosphors were fine powders with a particle size of 50 nm. The effects of synthesizing conditions were also investigated and optimized, which included the synthesis temperature and the activator concentration on the luminescent intensity. Compared with SrMoO₄:Eu³⁺ phosphors prepared by Solid-state reaction SrMoO₄:Eu³⁺ phosphors prepared by combining sol-gel and solid-state route showed appropriate particle size and a higher emission intensity.     

Solvothermal synthesis and luminescent properties of Y2Ti2O7:Eu3+ spheres

Pyrochlore‐structured yttrium titanate phosphors activated by trivalent europium ions (Y₂Ti₂O₇(YT):Eu³⁺), with spherical morphology, were synthesized at different pH values by a solvothermal process. From the structural and morphological measurements, the annealing temperature had no effect on the spherical morphology of the YT:Eu³⁺ sample. The photoluminescence excitation and emission spectra were taken by activating the Eu³⁺ ions in the YT host lattice as functions of Eu³⁺ ion concentration and annealing temperature. The optimal doping concentration was found to be 4 mol%, exhibiting an excellent orange–red emission due to the highest intensity of the ⁵D₀ → ⁷F₁ transition. When the YT:Eu³⁺ phosphor was mixed with YAG:Ce³⁺ phosphor, a brilliant white light emission was achieved. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence and gamma-ray irradiation of SrAl2O4:Euand Y2O3:Eu phosphors

Y₂O₃:Eu³⁺ phosphor is a very attractive material for use as a red phosphor in many fields. SrAl₂O₄:Eu²⁺ belongs to long lasting phosphor (LLP) and it is a useful bluish-green luminescence material, which can also be a promising candidate as a simple and easy-to-use radiation detection element for visual display of two dimensional radiation distributions. In the present study, both these two kinds of phosphors were synthesized using high temperature solid state reactions. In our work, the influence of gamma-ray irradiation on the properties of these two kinds of phosphors was studied by comparing photoluminescence, brightness and the decay curve of unirradiated and gamma-ray-irradiated samples. Conclusions from the present work can be briefly summarized as follows. In irradiated samples, the brightness is decreased without sensible change in the wavelength distribution of the luminescence spectrum and in the decay kinetic upon gamma exposure. Moreover, the emission due to Eu³⁺→Eu²⁺ conversion in Y₂O₃:Eu³⁺ phosphors was not observed in our sample after irradiation to high exposure. Also the brightness of SrAl₂O₄:Eu²⁺ phosphor turned out to decrease after the exposition to ionizing radiation while the luminescence wavelength distribution remained unchanged. The reason for the effect of gamma-ray irradiation on the properties of phosphors is also discussed in the paper.     

Preparation and luminescent properties of phosphor MGd2(MoO4)4: Eu (M=Ca, Sr and Ba)

Intense red emitting phosphors MGd₂(MoO₄)₄: Eu³⁺ (M=Ca, Sr and Ba) have been synthesized by the simple sol-gel technique. The formation processes and the phase impurity of phosphors are characterized by thermogravimetry-differential thermal analysis (TG-DTA) and power X-ray diffraction (XRD). The narrower size distribution and the regular shape of the phosphor particles are also measured by Field emission scanning electronic microscopy (FE-SEM). Photo-luminescent properties of the phosphors are performed at room temperature. Their excitation spectra present strong absorption at 395 nm near-UV light and 465 nm blue light, which match well with commercial LED chips. The phosphors exhibit satisfactory and excellent red light dominated by 616 nm and their photoluminescence intensity is about 3-4 times stronger than that of phosphor YAG under the 465 nm excitation. In addition, the optimal concentrations of Eu³⁺ for phosphors MGd₂(MoO₄)₄ (M=Ca, Sr and Ba) have also been determined.     

Luminescent properties of Dy doped SrMoO4 phosphor

Trivalent dysprosium ions (Dy³⁺) doped strontium molybdate (SrMoO₄) phosphors were synthesized by solid-state reaction and their photoluminescence (PL) properties were investigated. X-ray powder diffraction (XRD) analysis confirmed the formation of SrMoO₄:Dy³⁺. PL measurements indicated that the phosphor exhibited intense emission at 482, 490 (⁴F_9/2→⁶H_15/2) and 575 nm (⁴F_9/2→⁶H_13/2) under UV excitation. The effect of the doping concentration of Dy³⁺in SrMoO₄:Dy³⁺ on the PL was investigated in detail. Na⁺ ion was a good charge compensator for SrMoO₄:Dy³⁺.     

Studies in crystal structure and luminescence properties of Eu-doped metal tungstate phosphors for white LEDs

The correlation between the crystal structure and luminescent properties of Eu³⁺-doped metal tungstate phosphors for white LEDs was investigated. Red-emitting A_4−3x(WO₄)₂:Eu_x³⁺ (A=Li, Na, K) and B_(4−3x)/2(WO₄)₂:Eu_x³⁺ (B=Mg, Ca, Sr) phosphors were synthesized by solid-state reactions. The findings confirmed that these phosphors exhibited a strong absorption in the near UV to green range, due to the intra-configurational 4f-4f electron transition of Eu³⁺ ions. The high doping concentration of Eu³⁺ enhanced the absorption of near UV light and red emission without any detectable concentration quenching. Based on the results of a Rietveld refinement, it was attributed to the unique crystal structure. In the crystal structure of the Eu³⁺-doped metal tungstate phosphor, the critical energy transfer distance is larger than 5 Å so that exchange interactions between Eu³⁺ ions would occur with difficulty, even at a high doping concentration. The energy transfer between Eu³⁺ ions, which causes a decrease in red emission with increasing concentration of Eu³⁺, appears to be due to electric multi-polar interactions. In addition, the Eu-O distance in the host lattice affected the shape of emission spectrum by splitting of emission peak at the ⁵D₀→⁷F₂ transition of Eu³⁺.     

A potential red phosphor LiGd(MoO4)2:Eu for light-emitting diode application

Eu³⁺-doped LiGd(MoO₄)₂ red phosphor was synthesized by solid-state reaction, and its photoluminescent properties were measured. The effect of Eu³⁺ doping concentration on PL intensity was investigated, and the optimum concentration of Eu³⁺ doped in LiGd(MoO₄)₂ was found to be 30 mol%. Compared with Y₂O₂S:0.05Eu³⁺, Na_0.5Gd_0.5MoO₄:Eu³⁺ and KGd(MoO₄)₂:Eu³⁺, the LiGd(MoO₄)₂:Eu³⁺ phosphor showed a stronger excitation band around 395 nm and a higher intensity red emission of Eu³⁺ under 395 nm light excitation. For the first time, intensive red light-emitting diodes (LEDs) were fabricated by combining phosphor and a 395 nm InGaN chip, confirming that the LiGd(MoO₄)₂:Eu³⁺ phosphor is a good candidate for LED applications.     

Infrared-to-visible upconversion emission of Er3+/Yb3+-codoped SrMoO4 phosphors as wide-range temperature sensor

Er³⁺/Yb³⁺-codoped SrMoO₄ phosphors were prepared by a high-temperature solid-state reaction method. At room temperature, all the as-prepared samples exhibited strong upconversion properties and the emission intensity increased dramatically with the increase of Yb³⁺ ion concentration, reaching its maximum value when the concentration was 5 mol%. The dependence of emission intensity on the pump power suggested that the upconversion emission was a two-photon process. Furthermore, the optical temperature sensing properties based on green upconversion emissions of the SrMoO₄:0.01Er³⁺/0.05Yb³⁺ phosphor were studied. It is found that the SrMoO₄:0.01Er³⁺/0.05Yb³⁺ phosphor can be operated over a very wide temperature range of 93–773 K with a maximum sensitivity of ∼0.0128 K⁻¹, indicating that low- and high-temperature thermometry can be simultaneously realized in this phosphor.     

Preparation and photoluminescence properties of a new orange–red Ba3P4O13:Eu phosphor

A new orange–red Ba₃P₄O₁₃:Eu³⁺ phosphor has been synthesized by solid-state technique, and its photoluminescence properties were investigated. X-ray powder diffraction (XRD) analysis indicates that doping Eu³⁺ does not change the lattice of Ba₃P₄O₁₃. Field-emission scanning electron microscope (FE-SEM) images illustrate that microstructure of the phosphor consists of oval grains with average diameter of 1 μm and heavy agglomerate phenomenon. The excitation spectra indicate the phosphor can be effectively excited by near ultraviolet (NUV) light, making it attractive as conversion phosphor for LED applications. The phosphor exhibits a bright orange–red emission excited by 394 nm light. The CIE chromaticity can be varied slightly by adjusting the content of Eu³⁺, which is attributed to the different lattice sites occupied by Eu³⁺ in Ba₃P₄O₁₃ host. The photoluminescence studies indicate that Ba₃P₄O₁₃:Eu³⁺ is a potential orange–red phosphor for near-ultraviolet InGaN-based white light-emitting diodes (WLEDs).     

The effect of flux materials on the physical and optical properties of Eu-activated yttrium oxide phosphors

A flux fusion method was used to obtain the various sizes of Eu³⁺-activated Y₂O₃ red phosphors. The flux material was selected as an independent variable to control the physical properties of phosphor particles and their effects on the morphology and size distribution of phosphors were examined by scanning electron microscopy. The concentration of the flux materials and synthetic temperature were optimized for maximal photoluminescence intensity. Fluoride-based flux materials were found to work for the crystal formation of Eu³⁺-activated Y₂O₃. In particular, when a BaF₂ flux was used during the reaction at 1450 °C for 3 h, the photoluminescence (PL) intensity of Eu³⁺-activated Y₂O₃ was 25% higher than that without a flux and spherical phosphors had a mean particle size of 4-5 μm. The morphology and size distribution of the synthesized Eu³⁺-activated Y₂O₃ phosphor were predominantly dependent upon the type and concentration of flux material and synthetic temperature.     

A potential red-emitting phosphor CaSrAl2SiO7:Eu for near-ultraviolet light-emitting diodes

A novel red-emitting phosphor CaSrAl₂SiO₇:Eu³⁺ was firstly synthesized through the high temperature solid state reaction at 1300 °C. The structure, diffuse reflection spectra, photoluminescence spectra, color-coordinate parameters and quantum efficiencies (QE) of phosphors were investigated. The obtained CaSrAl₂SiO₇:Eu³⁺ phosphors have the same structure with that of the Ca₂Al₂SiO₇ and Sr₂Al₂SiO₇ phosphor, which have the melilite structure. Optical properties were studied as a function of Eu³⁺ concentration x, when x>0.14, the intensity of absorption of the f–f transitions of Eu³⁺ at 393 nm is stronger than that of the broad charge transfer transition band (CTB) around 254 nm, and which matches well with the output lights of NUV–LEDs, whereas, the concentration of Eu³⁺x≤0.14, the absorption of 393 nm is weaker than that of CTB. The underlying reason of Eu³⁺ concentration on their luminescent properties was investigated and discussed in detail. As a result, comparing with the commercial red phosphor Y₂O₂S:Eu³⁺, the CaSrAl₂SiO₇:xEu³⁺ (x>0.14) phosphor exhibited excellent color purity and much higher brightness and could be considered as promising red phosphors for NUV–LEDs.     

Effects of flux on crystal structure and luminescent properties of nitroxides phosphors

Yellow-green-emitting Sr Si2O2N2:Eu2+phosphors were synthesized with Sr2Si O4:Eu2+as precursor.The effects of flux and the concentration of Eu2+on the crystal structure and luminescent properties of the phosphors were investigated.Results suggested that the optimal content of flux Na2CO3 was 1 wt%and the optimal doping concentration of Eu2+was 0.05 mol.The emission spectra showed the most intense peaks located at 535 nm which corresponded to the 4f65d→4f7 transition of Eu2+.The excitation spectra showed that these phosphors could be effectively excited by near-ultraviolet and blue light,whichwas consistent with the widely applied output wavelengths of near-ultraviolet and blue-white light-emitting diode(LED)chips.When the influence of flux on the luminescent properties of Sr Si2O2N2:Eu2+phosphor was analyzed,the X-ray diffraction(XRD)patterns indicated that the flux could help the crystallization of the phosphors.No other phases except the triclinic structure of Sr Si2O2N2 were formed.The thermal stability and the emission intensity of synthesized Sr Si2O2N2:Eu2+phosphor were examined and compared with commercial YAG yellow phosphors.All results indicate that the yellow-green-emitting phosphor is a suitable candidate for the fabrication of white LEDs.     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Synthesis and luminescence properties of Eu3+,Bi3+-doped BaWO4 phosphors

BaWO₄:Eu³⁺,Bi³⁺ phosphors have been prepared by the conventional high-temperature solid-state reaction and chemical precipitation. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) technologies. When the phosphors are prepared by the high-temperature solidstate reaction, Bi³⁺ doping into BaWO₄:Eu³⁺ can increase the emission intensity of 613 nm. However, maximum emission at about 595 nm was observed in Eu³⁺,Bi³⁺-doped BaWO₄ phosphors prepared by the chemical precipitation. The decay constants (monitored at 595 and/or 613 nm) are within 45–100 s. The color purity of the Ba_0:865WO₄: Eu_0:11,Bi_0:025 phosphor (prepared by chemical precipitation) was 100%. The emission mechanism of Eu³⁺,Bi³⁺ in the BaWO₄ phosphors is briefly discussed.     

Enhanced luminescent properties of long-persistent Sr2MgSi2O7:Eu, Dy phosphor prepared by the co-precipitation method

Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors were prepared by the (aminopropyl)-triethoxysilane (APTES) co-precipitation method. Effects of synthesis temperature on the crystal characteristics, luminescent properties and afterglow performance of Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors have been discussed in detail and compared with the corresponding commercial product. The experimental results indicated that the sample could be synthesized at a relatively lower temperature and had better performance on the above-mentioned properties using the co-precipitation method.     

Synthesis and characterization of novel red emitting nanocrystal Gd6WO12:Eu phosphors

Novel nanosized Gd₆WO₁₂:Eu³⁺ phosphors were synthesized via a co-precipitation reaction. The crystal structure and morphology of the phosphors were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). It was found that the resultant powders show a regular and sphere-like shape with average particle size of 60 nm. Intrinsic red emission originating from Eu³⁺ was observed while excited at the W⁶⁺→O²⁻ and Eu³⁺→O²⁻ charge transfer bands or f-f absorption bands. The color coordinates of the phosphors were calculated to be x=0.625, y=0.375. The concentration dependence of the luminescence was studied, and optimum doping concentration for obtaining maximum emitting intensity was confirmed to be around 12 mol%. It was also found that the electric dipole-dipole interaction plays an important role for quenching luminescence of Eu³⁺.     

白光LED用LiBaBO3:Eu2+材料发光特性研究

采用高温固相法制备了LiBaBO₃:Eu²⁺绿色发光材料.测量了Eu²⁺浓度为1mol%时样品的激发与发射光谱,其发射光谱为双峰宽谱,主峰分别为482和507nm,与理论计算值符合很好;监测482nm发射峰时,对应激发光谱的峰值为287和365nm,监测507nm发射峰时,对应的激发峰为365和405nm.研究了Eu²⁺浓度对材料发射光谱的影响,结果显示,随Eu²⁺浓度的增大,蓝、绿发射峰均发生了     

Luminescence properties of Tm co-doped Sr2Si5N8:Eu red phosphor

The Sr₂Si₅N₈:Eu²⁺ phosphors, both undoped and doped with Tm³⁺, were synthesized by high temperature solid-state method. The XRD pattern shows that only Sr₂Si₅N₈ phase is formed whatever Tm³⁺ was doped or not. The peak positions of both phosphors are centered at 612 nm which is assigned to the 4f⁶5d→4f⁷ transition of Eu²⁺. It implies that the crystal field, which affects the 5d electron states of Eu²⁺, is not changed dramatically after the phosphor is doped with Tm³⁺. The afterglow time is about 10 min after Tm³⁺ ion is introduced into the phosphor. The concentration of Tm³⁺ has little influence on the afterglow time of the phosphor. The depths of trap energy level of the two phosphors were calculated based on the TL spectra. The depths of Sr₂Si₅N₈:Eu²⁺ and Sr₂Si₅N₈:Eu²⁺, Tm³⁺ are 1.75 and 1.01 eV, respectively.     

Synthesis,characterization and studies of radiative properties on Eu3+-doped ZnAl2O4

Eu³⁺-doped ZnAl₂O₄ phosphors were successfully synthesized in air atmosphere at 900 °C. The phosphors were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermally stimulated luminescence (TSL) and photoluminescence (PL) techniques. The average particle size of the system as determined from SEM was found to be 100–150 nm (for samples annealed at 900 °C). PL spectra of the doped phosphors showed emission peaks corresponding to Eu³⁺ ions. Lifetime studies revealed Eu³⁺ ions to be in two different sites. The asymmetric ratio (I₆₁₆/I₅₉₂) was observed to be about 3.75. This suggested that Eu³⁺ ion entered the host mainly substituting Al³⁺ site distorting the local environment and is partly located on surface of the phosphors. A prominent glow peak at 430 K was observed in the TSL of γ-irradiated Eu³⁺-doped ZnAl₂O₄ phosphors. Trap parameters for this peak have been determined and the probable mechanism for the glow peak is proposed. CIE chromaticity coordinates for the system were evaluated. It was observed that, the system could be employed as a potential red emitting phosphor. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. The PL intensity of the as prepared phosphors was 63% of that of the commercial phosphor. Apart from this, various radiative properties such as the Judd–Ofelt intensity parameters, spontaneous emission probabilities, luminescence branching ratios, radiative lifetimes and quantum efficiency were evaluated for the system.