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1.
A series of YAl3(BO3)4 phosphors doped with different concentrations of Dy2O3 (0.1≤x≤5 mol%) were prepared by solid-state reaction method. The crystallization process of the precursor has been examined by differential thermal analysis (DTA) measurements. The phase purity and surface morphological features were characterized by X-ray diffraction (XRD) and scanning electron microscopic (SEM) investigations. The YAl3(BO3)4 nanocrystals obtained were found to be about 45 nm in size and have the trigonal structure with some agglomeration. Fourier transform infrared (FTIR) and energy dispersive X-ray spectra (EDS) measurements were carried out to understand the compositional and elemental analysis. The characteristics emission peaks of Dy3+ ion corresponding to the transitions of 4F9/2→6H15/2 at 485 nm and 4F9/2→6H13/2 at 576 nm were observed in the emission spectra. The luminescence quenching noticed at higher Dy2O3 concentrations is due to the exchange interaction among the excited Dy3+ ions. 相似文献
2.
In this paper, Ba3P4O13:Eu2+ phosphor was synthesized by a solid-state reaction. The photoluminescence (PL) emission spectrum and luminescence decay kinetics confirm that the doped Eu2+ ions can occupy two different Ba2+ sites. The PL excitation spectrum shows a broad band matching well with the emission of near-UV chip. Ba3P4O13:Eu2+ is a promising phosphor for near-UV chip excited white LEDs. The doped Eu3+ ions can also be reduced to Eu2+ ions in air atmosphere at high temperature. Charge compensation mechanism is applied to explain this kind of abnormal reduction. 相似文献
3.
Mixtures of ZrO2, SiO2, Pr2O3, and H3BO3 were fired at the temperature of 1150–1350 °C under H2 atmosphere. A single phase ZrSiO4:Pr phosphors could be achieved at the firing temperature above 1150 °C. Crystallinity and PL properties strongly depended on the flux amounts, firing temperature, and dopant concentrations. ZrSiO4:Pr phosphors showed a strong red emission at 615 nm and a weak red emission at 622 nm with an excitation wavelength of 295 and 450 nm, respectively. Two sets of the emission bands and excitation spectra originated from Pr3+ ions at Zr and Si sites, respectively. 相似文献
4.
Red-light-emitting phosphors of La2Mo2O9:Pr3+ and S-doped La2Mo2O9:Pr3+ were prepared by high temperature solid state reaction. Under the excitation of 450 nm blue light, all samples produced a red emission peak at 650 nm corresponding to the characteristic transition of Pr3+ (3P0→3F2). The dependence of Pr3+ doping content (x) on the luminescent intensity was analyzed, and the optimal doping content of Pr3+ was x=0.07. After a small quantity of sulfur was introduced into the system, the luminescence intensity of phosphors was obviously enhanced. The reasons for the enhancement of luminescence are due to improved crystallization after S doping and the relatively large electronegativity difference between S and Mo. Additionally, the coincidence of the excitation wavelength with the emission of GaN chips may recommend this phosphor system as a potential candidate for use in white light-emitting diodes. 相似文献
5.
Ce2(WO4)3 ceramics have been synthesized by the conventional solid-state ceramic route. Ce2(WO4)3 ceramics sintered at 1000 °C exhibited ?r = 12.4, Qxf = 10,500 GHz (at 4.8 GHz) and τf = −39 ppm/°C. The effects of B2O3, ZnO–B2O3, BaO–B2O3–SiO2, ZnO–B2O3–SiO2 and PbO–B2O3–SiO2 glasses on the sintering temperature and microwave dielectric properties of Ce2(WO4)3 were investigated. The Ce2(WO4)3 + 0.2 wt% ZBS sintered at 900 °C/4 h has ?r = 13.7, Qxf = 20,200 GHz and τf = −25 ppm/°C. 相似文献
6.
Zhongfei Mu Yihua Hu Li Chen Xiaojuan Wang Guifang Ju Zhongfu Yang Ren Chen 《Ceramics International》2014
Stoichiometric phosphors LiGd1−xEux(PO3)4(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via traditional solid state reactions. The X-ray powder diffraction measurements show that all prepared samples are isostructural with LiNd(PO3)4. Eu3+ doped phosphors can emit intense reddish orange light under the excitation of near ultraviolet light from 370 to 410 nm. The strongest two at 591 and 613 nm can be attributed to the transitions from excited state 5D0 to ground states 7F1 and 7F2, respectively. The typical chromaticity coordinates (x=0.620, y=0.368) of Eu3+ doped phosphors are in red area. The recorded absorbance spectra indicate that there is effective absorbance in the near UV region for all Eu3+ doped samples. Present research indicates that LiGd1–xEux(PO3)4 is a promising phosphor for white light-emitting diodes. 相似文献
7.
Eu2+ and Mn2+ singly doped and Eu2+/Mn2+-codoped Ca4Mg5(PO4)6 phosphors were synthesized via combustion synthesis. Mn2+-singly doped Ca4Mg5(PO4)6 phosphor exhibits a single red emission in the wavelength range of 500–700 nm due to the 4T1(4G)→6A1(6S) transition of Mn2+. Eu2+/Mn2+ co-doped phosphor emits two distinctive luminescence bands: a blue one centered at 442 nm originating from Eu2+ and a broad red-emitting one peaked at 609 nm from Mn2+. Energy transfers from Eu2+ to Mn2+ were discovered by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the systematic relative decline and growth of emission bands of Eu2+ and Mn2+, respectively. Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu2+ and Mn2+. 相似文献
8.
Eu-based vanadate Ca9Eu(VO4)7 phosphor was synthesized by the solid state reaction method and was characterized by X-ray powder diffraction (XRD). The photoluminescence excitation and emission spectra, fluorescence decay curves and the dependence of luminescence intensity on temperature were investigated. The phosphor can be efficiently excited by near UV light to realize an intense red luminescence (614 nm) corresponding to the electric dipole transition 5D0 → 7F2 of Eu3+ ions. The crystallographic site-occupations of the Eu3+ ions in Ca9Eu(VO4)7 were investigated by the site-selective excitation and emission spectra, and the fluorescence decay curves in the 5D0 → 7F0 region using a pulsed, tunable, narrowband dye laser. The red luminescence together with the thermal stability was discussed on the base of the Eu3+ site-distribution in Ca9Eu(VO4)7 host. 相似文献
9.
The microwave dielectric properties of Sm(Mg0.5Ti0.5)O3 incorporated with various amount of Bi2O3 and B2O3 additives have been investigated systematically. In this study, both Bi2O3 and B2O3 additives acting as a sintering aid can effectively lower the sintering temperature from 1550 °C to 1300 °C. The ionic radius of Bi3+ for a coordination number of 6 is 0.103 nm, whereas the ionic radius of B3+ is 0.027 nm. Clearly, the ionic radius of Bi3+ is greatly larger than one of B3+, which resulted in the specimens incorporated with Bi2O3 having larger lattice parameters and cell volume than those incorporated with B2O3. The experimental results show that no second phase was observed throughout the entire experiments. Depending on the interfacial tension, the liquid phase may penetrate the grain boundaries completely, in which case the grains will be separated from one another by a thin layer as shown in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with Bi2O3. Whereas, in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with B2O3, the volume fraction of liquid is high, the grains may dissolve into the liquid phase, and rapidly rearrange, in which case contact points between agglomerates will be dissolved due to their higher solubility in the liquid, leading plate-like shape microstructure.A dielectric constant (?r) of 29.3, a high Q × f value of 26,335 GHz (at 8.84 GHz), and a τf of −32.5 ppm/°C can be obtained for Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 10 mol% Bi2O3 sintered at 1300 °C. While Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 5 mol% B2O3 can effectively lower temperature coefficient of resonant frequency, which value is −21.6 ppm/°C. The Sm(Mg0.5Ti0.5)O3 ceramic incorporated with heavily Bi2O3 and B2O3 additives exhibits a substantial reduction in temperature (∼250 °C) and compatible dielectric properties in comparison with that of an un-doped one. This implied that this ceramic is suitable for miniaturization in the application of dielectric resonators and filters by being appropriately incorporated with a sintering aid. 相似文献
10.
Color tunable yellow-emitting phosphors of Sr5−5xEu5x(PO4)2SiO4 (x = 0.05-0.15) were prepared by conventional solid-state reaction method. The X-ray powder diffraction patterns, the photoluminescence excitation and emission spectra were measured. The main excitation bands of the phosphors locate at a broad band extending from 300 to 500 nm, which can match the emission of ultraviolet- and blue-emitting diode chips. The tunable luminescence color was realized by the changing Eu2+ doping in Sr5(PO4)2SiO4. The structure and luminescence properties were investigated. Sr5−5x(PO4)2SiO4:Eu5x displays two typical luminescence centers, which originate from two different Sr2+ (Eu2+) sites in the host. The site-occupation, the luminescence intensity and energy transfer between the Eu2+ ions occupying two different crystallographic Sr2+ sites were discussed on the base of the luminescence spectra and crystal structure. This is helpful to improve this phosphor for a potential application as a white light emitting diode phosphor. 相似文献
11.
Tb3+-doped La1−xAlO3 phosphor powders are successfully synthesized by the solution combustion method, using citric acid as the combustion fuel. The crystal structure and photoluminescence properties of La1−xAlO3:xTb3+ phosphors are studied, depending on Tb3+ content. The strongest emission peak is found at 543 nm, which originates from the 5D4→7F5 transition of Tb3+ ions, indicating green emission. Among the fabricated phosphors, the La0.9AlO3:0.1Tb3+ phosphor emits the strongest green light. The excellent luminescent properties make it a possible candidate for white light-emitting diodes and various photonic applications. 相似文献
12.
Preparation of Sr2SiO4:Eu phosphors by microwave-assisted sintering and their luminescent properties
An Eu3+ activated strontium silicate phosphor was synthesized using a microwave-assisted sintering with a flux NH4Cl. X-ray powder diffraction analysis confirmed the formation of pure Sr2SiO4 phase without second phase or phases of starting materials as Sr1.9SiO4:Eu3+0.1 powders sintered at various temperatures in microwave furnace for 1 h. Scanning electron microscopy showed smaller particle size and more uniform grain size distributions are obtained by microwave-assisted sintering. In the PL studies, the excitation spectrum of Sr1.9SiO4:Eu3+0.1 phosphors exhibited a broad band in the UV region centered at about 270 nm which was consistent with the absorption spectra. Both microwave sintered and conventionally sintered powders emitted a maximum luminescence centered at 617 nm under excitation of 395 nm, with similar luminescent intensity. The results showed that microwave processing has the potential to decrease the sintering time and required energy input for the production of Sr1.9SiO4:Eu3+0.1 phosphors without degrading photoluminescence. 相似文献
13.
Transparent disordered BMT ceramics were obtained by solid state reaction. Sn4+ ions were incorporated to make the B site of the perovskite structure disordered. The stoichiometric powder mixture with and without Sn doping was calcinated at 1300 °C, respectively and they were both characterized. After dry pressing, the pellets with Sn doping were sintered at 1600 °C in oxygen atmosphere for 4 h. The grain size of the transparent ceramics is around 12 μm. No pores were detected in or among the grains. The inline transmittance of the material is 66% at 580 nm. The refractive index is 2.09 at 1600 nm. 相似文献
14.
In this work, we prepared CaSr1-xAl2SiO7:xCe3+ (0.03 ≤ x ≤ 0.12) and CaSr0.94Al2SiO7:0.03Ce3+,0.03 M+ (M+ = Li+ and Na+) phosphors via solid-state reaction method. Structural and photoluminescence (PL) properties of the phosphors were also investigated. The prepared phosphors formed an orthorhombic crystal structure with the P212121 space group. CaSr1-xAl2SiO7:xCe3+ phosphors were effectively excited by near-ultraviolet (UV) light (345 nm), which is suitable with the emission of near-UV light emitting diode chips. A broad blue emission (402 nm) was detected in CaSr1-xAl2SiO7:xCe3+ and CaSr0.94Al2SiO7:0.03Ce3+,0.03 M+ phosphors; this was attributed to the 4f05d1 → 4f1 transition of Ce3+. To maintain charge equilibrium, charge compensators, such as monovalent Li+ and Na+ ions, were doped into the CaSr0.97Al2SiO7:0.03Ce3+ phosphor, significantly improving its PL properties. The strongest emission intensity was achieved in CaSr0.94Al2SiO7:0.03Ce3+,0.03Li+ phosphor. Addition of Li+ charge compensator was highly effective in improving PL properties of CaSr0.97Al2SiO7:0.03Ce3+ phosphors. 相似文献
15.
YTaO4:Eu3+ powders were synthesized by a flux method with LiCl. The use of a flux in the synthesis of M′–YTaO4 facilitated the reaction of raw materials, leading to lowering the heating temperature, but not effective at the high firing temperature. The red emission peaks were observed around 613 nm with an excitation wavelength of 254 nm. Emission peaks were composed of two sets around 613 nm and 590 nm, which originated from 5D0–7F2 and 5D0–7F1, respectively. PL intensity of YTaO4:Eu3+ prepared with a small amount of LiCl (10 wt%) significantly depended on the firing temperatures, while that with a larger amount of LiCl (40 wt%) slightly relied on firing temperatures. The highest PL intensity could be obtained at the firing conditions of 1300 °C and 10 wt% LiCl. 相似文献
16.
Vengala Rao BandiBhaskar Kumar Grandhe Kiwan Jang Ho-Sueb LeeSoung-Soo Yi Jung-Hyun Jeong 《Ceramics International》2011,37(6):2001-2005
The photoluminescent properties of un-doped and Sm3+ doped Ca3Y2Si3O12 phosphors were prepared by the citrate sol-gel method. Un-doped sample has shown a strong blue emission, which has its maximum intensity at 389 nm. Among all the observed emission transitions 4G5/2→6HJ (J = 5/2, 7/2 & 9/2) of Sm3+, the reddish-orange (RO) emission transition 4G5/2→6H7/2 is more prominent, which matches well with the emission wavelength of near UV (n-UV) LED. The reasons for the observance of such prominent visible color emissions from these phosphors have been substantiated appropriately. Besides, structural details of these samples have also been analyzed from the measured XRD, TEM, TG-DTA and FT-IR profiles. 相似文献
17.
《Ceramics International》2016,42(5):5737-5742
The novel red-emitting Eu3+ ions activated CaGd2(MoO4)4 phosphors were prepared by a citrate sol–gel method. The X-ray diffraction patterns confirmed their tetragonal structure when the samples were annealed above 600 °C. The photoluminescence excitation spectra of CaGd2(MoO4)4:Eu3+ phosphors exhibited the charge transfer band (CTB) and intense f–f transitions of Eu3+ ion. The optimized annealing temperature and Eu3+ ion concentration were analyzed for CaGd2(MoO4)4:Eu3+ phosphors based on the dominant red (5D0→7F2) emission intensity under NUV (394 nm) excitation. All decay curves were well fitted by the single exponential function. These luminescent powders are expected to find potential applications such as WLEDs and optical display systems. 相似文献
18.
The red-emitting (Y1−xGdx)0.94Eu0.06VO4 (0 ≤ x ≤ 1.0) phosphors were synthesized by ultrasonic spray pyrolysis. The (Y1−xGdx)0.94Eu0.06VO4 (0 ≤ x ≤ 1.0) phosphors had the tetragonal xenotime structure with a space group of I41/amd (1 4 1). The calculated crystallite sizes of the annealed phosphors ranged from 58 to 68 nm. In this study, we discussed the photoluminescence properties of the (Y1−xGdx)0.94Eu0.06VO4 phosphors under VUV excitation, depending on Gd content. The emission intensity of the (Y1−xGdx)0.94Eu0.06VO4 phosphors increased with increasing Gd content up to x = 0.5, and then decreased with a further increase in Gd content. The purest red color was obtained for the (Y0.5Gd0.5)0.94Eu0.06VO4 phosphors. 相似文献
19.
J.C. Diez M.A. Torres Sh. Rasekh G. Constantinescu M.A. Madre A. Sotelo 《Ceramics International》2013
Ca3Co4−xCrxO9 polycristalline thermoelectric ceramics with small amounts of Cr have been synthesized by the classical solid state method. Microstructural characterizations have shown that all the Cr has been incorporated into the Ca3Co4O9 structure and no Cr-containing secondary phases have been produced for Cr contents≤0.05. Apparent density measurements have shown that all samples are very similar, with densities around 75% of the theoretical one. Electrical resistivity decreases and Seebeck coefficient slightly raises when Cr content increases until 0.05 Cr addition. The improvement in both parameters leads to higher power factor values than the usually obtained by conventional solid state routes. 相似文献
20.
Latha Kumari W.Z. Li Charles H. Vannoy Roger M. Leblanc D.Z. Wang 《Ceramics International》2009,35(8):3355-3364
Magnesium hydroxide (Mg(OH)2) micro- and nanostructures have been synthesized by a single step hydrothermal route. Surface morphology analysis reveals the formation of micro- and nanostructures with varying shape and size at different synthesis conditions. Structural investigations by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the synthesized material is Mg(OH)2 with hexagonal crystal structure. An optical band gap of 5.7 eV is determined for Mg(OH)2 nanodisks from the UV–vis absorption spectrum. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of Mg(OH)2 nanodisks at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancies in the material. Furthermore, Mg(OH)2 has been converted to MgO by calcination at 450 °C. Optical studies of the MgO nanodisks have shown an optical band gap of 3.43 eV and a broadband PL emission in the UV region. Mg(OH)2 and MgO nanostructures with wide-band gap and short-wavelength luminescence emission can serve as a better luminescent material for photonic applications. 相似文献