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1.
Xinghua Zhang Zunming Lu Fanbin MengFang Lu Long HuXuewen Xu Chengchun Tang 《Materials Letters》2012,66(1):16-18
A series of yellow-emitting phosphors based on a silicate host matrix, Ca3 − xSi2O7: xEu2+, was prepared by solid-state reaction method. The structure and photoluminescent properties of the phosphors were investigated. The XRD results show that the Eu2+ substitution of Ca2+ does not change the structure of Ca3Si2O7 host and there is no impurity phase for x < 0.12. The SEM images display that phosphors aggregate obviously and the shape of the phosphor particle is irregular. The EDX results reveal that the phosphors consist of Ca, Si, O, Eu and the concentration of these elements is close to the stoichiometric composition. The Ca3 − xSi2O7: xEu2+ phosphors can be excited at a wavelength of 300-490 nm, which is suitable for the emission band of near ultraviolet or blue light-emitting-diode (LED) chips. The phosphors exhibit a broad emission region from 520 to 650 nm and the emission peak centered at 568 nm. In addition, the shape and the position of the emission peak are not influenced by the Eu2+ concentration and excitation wavelength. The phosphor for x = 0.045 has the strongest excitation and emission intensity, and the Ca3 − xSi2O7: xEu2+ phosphors can be used as candidates for the white LEDs. 相似文献
2.
The Gd2(TixZr1 − x)2O7 (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd2(TixZr1 − x)2O7 were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd2(TixZr1 − x)2O7 from room temperature to 1400 °C was measured by a laser-flash method. The Gd2Zr2O7 has a defect fluorite-type structure; however, Gd2(TixZr1 − x)2O7 (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd2Zr2O7 and Gd2Ti2O7 are infinitely soluable. The thermal conductivity of Gd2(TixZr1 − x)2O7 increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd2(TixZr1 − x)2O7 first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd2(TixZr1 − x)2O7 is within the range of 1.33 to 2.86 W m− 1 K− 1 from room temperature to 1400 °C. 相似文献
3.
Guifang JuYihua Hu Haoyi WuZhongfu Yang Chujun FuZhongfei Mu Fengwen Kang 《Optical Materials》2011,33(8):1297-1301
A series of Eu3+ activated Li6Y1−xEux(BO3)3 (0.05 ? x ? 1) phosphors were synthesized by solid-state reaction method. The structures and photoluminescent properties of the phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the monoclinic Li6Gd(BO3)3. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370-410 nm) light. The red emission from transition 5D0→7F2 is dominant. The emission spectra exhibit strong red performance (CIE chromaticity coordinates: x = 0.65, y = 0.35), which is due to the 5D0−7FJ transitions of Eu3+ ions. The relationship between the structure and the photoluminescent properties of the phosphors was studied. The concentration quenching occurs at x ≈ 0.85 under near UV excitation. Li6Y(BO3)3:Eu3+ has potential application as a phosphor for white light-emitting diodes. 相似文献
4.
(Gd1−x,Eux)2O2SO4 nano-phosphors were synthesized by a novel co-precipitation method from commercially available Gd2O3, Eu2O3, H2SO4 and NaOH starting materials. Composition of the precursor is greatly influenced by the molar ratio of NaOH to (Gd1−x,Eux)2(SO4)3 (the m value), and the optimal m value was found to be 4. Fourier transform infrared spectrum (FT-IR) and thermal analysis show that the precursor (m = 4) can be transformed into pure (Gd1−x,Eux)2O2SO4 nano-phosphor by calcining at 900 °C for 2 h in air. Transmission electron microscope (TEM) observation shows that the Gd2O2SO4 phosphor particles (m = 4) are quasi-spherical in shape and well dispersed, with a mean particle size of about 30-50 nm. Photoluminescence (PL) spectroscopy reveals that the strongest emission peak is located at 617 nm under 271 nm light excitation, which corresponds to the 5D0 → 7F2 transition of Eu3+ ions. The quenching concentration of Eu3+ ions is 10 mol% and the concentration quenching mechanism is exchange interaction among the Eu3+ ions. Decay study reveals that the 5D0 → 7F2 transition of Eu3+ ions has a single exponential decay behavior. 相似文献
5.
Eu3+-substituted SrTiO3 (Sr1 − xEuxTiO3) without second phase has been successfully prepared by Pechini method. X-ray diffraction patterns have suggested that solid-solubility limit would be 1-2 mol% due to large ionic radius difference between Eu3+ and Sr2+. Photoluminescence spectra of Sr1 − xEuxTiO3 have shown the intense 5D0-7F1 transition higher than 5D0-7F2 transition, which indicates that Eu3+ was substituted for Sr2+ site. 相似文献
6.
(Gd1−x,Eux)2O2SO4 sub-microphosphors were synthesized by homogeneous precipitation method from commercially available Gd2O3, Eu2O3, H2SO4 and (NH2)2CO (urea) starting materials. Fourier transform infrared spectra show that the precursors with different molar ratios of (NH2)2CO to Gd2(SO4)3 (the m value) are mostly composed of gadolinium hydroxyl, carbonate and sulfate groups with some crystal water. X-ray diffraction indicated that the precursor (m = 5) can be transformed into pure Gd2O2SO4 phase after heat treated at 900 °C for 2 h in air. Field emission scanning electron microscope micrographs illustrate that the Gd2O2SO4 phosphor particles (m = 5) are quasi-spherical in shape and well dispersed, with a mean particle size of about 300–500 nm. Photoluminescence spectroscopy reveals that the strongest emission peak for (Gd1−x,Eux)2O2SO4 sub-microphosphors is located at 618 nm under 270 nm light excitation, which corresponds to the 5D0 → 7F2 transition of Eu3+ ions. The quenching concentration of Eu3+ ions is 5 mol% and the concentration quenching mechanism is due to the electric dipole–dipole interaction. Decay study reveals that the 5D0 → 7F2 transition of Eu3+ ions fits with a mono exponential function. 相似文献
7.
Gd2O3 nanophosphors were prepared by combustion synthesis with and without doping of Dy3+ ions. The X-ray powder diffraction patterns indicate that as-prepared Gd2O3 and 0.1 mol% Dy2O3 doped Gd2O3 nanophosphors have monoclinic structures. The transmission electron microscope (TEM) studies revealed that the as-prepared phosphors had an average crystallite sizes around 37 nm. The excitation and emission properties have been investigated for Dy3+ doped and undoped Gd2O3 nanophosphors. New emission bands were observed in the visible region for Gd2O3 nanophosphors without any rare earth ion doping under different excitations. A tentative mechanism for the origin of luminescence from Gd2O3 host was discussed. Emission properties also measured for 0.1 mol% Dy3+ doped Gd2O3 nanophosphors and found the characteristic Dy3+ visible emissions at 489 and 580 nm due to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. The chromaticity coordinates were calculated based on the emission spectra of Dy3+ doped and undoped Gd2O3 nanophosphors and analyzed with Commission Internationale de l'Eclairage (CIE) chromaticity diagram. These nanophosphors exhibit green color in undoped Gd2O3 and white color after adding 0.1 mol% Dy2O3 to Gd2O3 nanophosphors under UV excitation. These phosphors could be a promising phosphor for applications in flat panel displays. 相似文献
8.
Congbing Tan Yunxin Liu Wenbin LiYutao Zhang Yunan Han 《Materials Science and Engineering: B》2011,176(16):1251-1256
Lanthanide-doped uniform pure cubic phase Y2O3 hollow microspheres have been successfully synthesized via a facile, high yield urea-based coprecipitation route with assistant of carbon spheres templates. The diameter and shell thickness of the microspheres can be manipulated by adjusting carbon sphere templates. Under a 980 nm excitation, Yb3+/Er3+, Er3+, Yb3+/Tm3+-doped Y2O3 hollow microspheres emit bright upconversion red, green, blue light with high purity, respectively, while Eu3+, Eu3+/Tb3+-doped Y2O3 hollow microspheres exhibit intense downconversion red light under the excitation of 254 nm ultraviolet light. Especially, the 610 nm emission intensity of Eu3+ in the Eu3+/Tb3+-codoped Y2O3 hollow microspheres is almost 5 times of that in the Y2O3:Eu3+ hollow microspheres indicating the occurring of the energy transfer from Tb3+ to Eu3+ ions. 相似文献
9.
Eu2+ and Dy3+ ion co-doped Sr3Al2O6 red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO3)2, Al(NO3)3·9H2O, Eu2O3, Dy2O3, H3BO3 and C6H8O7·H2O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr3Al2O6:Eu2+, Dy3+ phosphors was discussed. The emission peak of Sr3Al2O6:Eu2+, Dy3+ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr3Al2O6:Eu2+, Dy3+ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f65d1 → 4f7 transition of the Eu2+ ions in Sr3Al2O6. The afterglow time of (Sr0.94Eu0.03Dy0.03)3 Al2O6 phosphors lasts for over 600s after the excited source was cut off. 相似文献
10.
RE3+-activated monoclinic Na3GdP2O8 (RE3+ = Tb3+, Dy3+, Eu3+, Sm3+) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na3GdP2O8:RE3+ (RE3+ = Tb3+, Dy3+, Eu3+, Sm3+) were assigned and corroborated. For the sample Na3GdP2O8:5%Tb3+, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb3+. For Na3GdP2O8:5%Dy3+, the broad band at 176 nm could be related to the f-d transitions of Dy3+ and the O2− → Dy3+ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu3+ doped sample, the O2− → Eu3+ CTB is observed to be at 245 nm. For the Sm3+ doped sample, the O2− → Sm3+ CTB is not distinguished obviously and is overlapped with the host-related absorption band. 相似文献
11.
Lead-free thick film negative temperature coefficient (NTC) thermistors based on perovskite-type BaCoIIxCoIII2xBi1 − 3xO3 (x ≤ 0.1) were prepared by mature screen-printing technology. The microstructures of the thick films sintered at 720 °C were examined by X-ray diffraction and scanning electron microscopy. The electrical properties were analyzed by measuring the resistance-temperature characteristics. For the BaBiO3 thick films, the room-temperature resistivity is 0.22 MΩ cm, while the room-temperature resistivity is sharply decreased to about 3 Ω cm by replacing of Bi with a small amount of Co. For compositions 0.02 ≤ x ≤ 0.1, the values of room-temperature resistivity (ρ23), thermistor constant (B25/85) and activation energy are in the range of 1.995-2.975 Ω cm, 1140-1234 K and 0.102-0.111 eV, respectively. 相似文献
12.
13.
Xinguo Zhang 《Materials Letters》2009,63(11):852-854
Sr4Si3O8Cl4:Eu2+ and Sr3.5Mg0.5Si3O8Cl4:Eu2+ phosphors were prepared by a conventional solid state reaction (SS). Excited by 370 nm near-ultraviolet light, the phosphors show an efficient bluish-green wide-band emission centering at 484 nm, which originates from the 4f5d1 → 4f7 transition of Eu2+ ion. The excitation spectra of the phosphors are a broad band extending from 250 nm to 400 nm. Mg2+-codoping greatly enhances the bluish-green emission of the phosphors. An LED was fabricated by coating the Sr3.5Mg0.5Si3O8Cl4:0.08Eu2+ phosphor onto an ~ 370 nm-emitting InGaN chip. The LED exhibits bright bluish-green emission under a forward bias of 20 mA. The results indicate that Sr3.5Mg0.5Si3O8Cl4:0.08Eu2+ is a candidate as a bluish-green component for fabrication of NUV-based white LEDs. 相似文献
14.
This paper reports an optical investigation of glass-ceramics formed by annealing glasses with compositions 50 GeO2-40 PbO-10 PbF2-x EuF3, x = [0.5; 1; 1.5; 2] and polycrystalline ceramics with composition 100 PbF2, y EuF3, with y = 5, 10, 15 and 20. For each material, the photoluminescence spectrum and the photoluminescence lifetimes of the 5D0, 5D1 and 5D2 Eu3+ levels are measured. Occurrence of Eu3+:β-PbF2 nanocrystallites in the glass-ceramics is confirmed and total ceramisation requires more than 10% of EuF3 with respect to PbF2 in the starting glass.In the Eu3+:β-PbF2 ceramics and glass-ceramics, Eu3+ ions replace Pb2+ in their regular cubic site, but they interact together to form dimers and higher nuclearity clusters. These two species are easily distinguished according to their photoluminescence decay rate. For the EuF3 rates investigated here, there are no isolated Eu3+ ions in the PbF2 lattice.A preliminary investigation of the optical properties of co-doped Gd3+:Eu3+:β-PbF2 ceramics was also performed. It shows that mixed Gd3+-Eu3+ dimers and clusters are formed, and that efficient Gd3+ → Eu3+ energy transfer occurs in these ceramics. The Pb2+ ions of the lattice may also be involved in the energy transfer process. 相似文献
15.
The vacuum ultraviolet excited luminescent properties of Eu3+, Tb3+, Dy3+, Sm3+ and Tm3+ in the matrices of Ca4Y6(SiO4)6O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca4Y6(SiO4)6O. For Eu3+-doped samples, the O2− → Eu3+ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb3+-doped samples. For Dy3+-doped and Sm3+-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm3+-doped samples, the O2− → Tm3+ CTB was located at 191 nm. About the color purity and emission intensity, Ca4Y6(SiO4)6O:Tb3+ is an attractive candidate of green light PDP phosphor, and Ca4Y6(SiO4)6O:Dy3+ has potential application in the field of mercury-free lamps. 相似文献
16.
Eu3+- and Tb3+-activated SrGdGa3O7 phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd1 − xEux)Ga3O7 and Sr(Gd1 − xTbx)Ga3O7 formed continuous solid solution in the range of x = 0-1.0. Unactivated SrGdGa3O7 exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa3O7:xEu3+ and SrGdGa3O7:xTb3+ phosphors also showed the well-known Eu3+ and Tb3+ excitation and emission. The energy transfer from Gd3+ to Eu3+ and Tb3+ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu3+ and Tb3+ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa3O7:Eu and SrGdGa3O7:Tb were compared with commercial phosphors, Y2O3:Eu and LaPO4:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu3+ and Tb3+ were in the range of microsecond. The energy transfer from Gd3+ to Tb3+ was also observed in decay curve. 相似文献
17.
Hongbin Liang Zifeng TianHuihong Lin Mubiao XieGuobin Zhang Pieter DorenbosQiang Su 《Optical Materials》2011,33(4):618-622
The spectroscopic properties of Na3Gd(PO4)2 and Na3Gd(PO4)2:Ce3+ phosphors in the VUV-UV spectral range were investigated. Five excitation bands of Ce3+ ions at Gd3+ sites are observed at wavelengths of 205, 246, 260, 292, and 321 nm. Doublet Ce3+ 5d → 4f emission bands are observed at 341 and 365 nm with a decay constant τ1/e around 26 ns. The X-ray excited luminescence of Na3Gd0.99Ce0.01(PO4)2 at room temperature shows a photon yield of ∼17,000 photons/MeV of absorbed X-ray energy. 相似文献
18.
The optical and electrical properties of vapour phase grown crystals of diluted magnetic semiconductor Zn1 − xCrxTe were investigated for 0 ≤ x ≤ 0.005. The diffuse reflectance spectra exhibited an increase in the fundamental absorption edge (E0) with composition x and were also dominated by a broad absorption band around 5200 cm− 1 arising from 5T2 → 5E transition. The 5T2 and 5E levels originate from the crystal field splitting of the 5D free ion in the ground state. The electrical resistivity measurements revealed semiconducting behaviour of the samples with p-type conductivity in the temperature range of 200-450 K. 相似文献
19.
Passive Q-switching laser operation of Nd:GdxY1−xVO4 mixed crystals at 671 nm has been compared in the same V-shape folded cavity. Based on our comparative analysis, the best laser characteristics - the highest pulse energy and peak power and the shortest pulse width - were demonstrated by Nd:Gd0.63Y0.37VO4 crystal. At the same time, this crystal possesses the lowest thermal conductivity in comparison with the other Nd:GdxY1−xVO4 crystals, which could result in decreasing the average laser output power. To verify this assumption we also measured the focal lengths of thermal lens induced in the crystals during the laser operation. 相似文献
20.
Jung-Sik Shin Hyun-Joon Kim Yong-Kwang Jeong Kwang-Bok Kim Jun-Gill Kang 《Materials Chemistry and Physics》2011
The highly efficient red phosphors (Ca1−xSrx)(S1−ySey):Eu2+,M3+ (M = Sc and Y) were prepared, starting from CaCO3, SrCO3, Eu2O3, Sc2O3, Y2O3, S, and SeO2 with a flux, by a conventional solid-state reaction. The optimized red phosphors converted 11.8% (Sc3+) and 11.7% (Y3+) of the absorbed blue light into luminescence. These quantum values are much higher than Q = 3.0% of CaS:Eu2+. For the fabrication of light-emitting diodes (LEDs), the prepared phosphors were coated with MgO from non-aqueous solution to overcome their weakness against moisture. White LEDs were fabricated by pasting the prepared red phosphors and the yellow YAG:Ce3+ phosphor on an InGaN blue chip (λems = 446.5 nm). The incorporation of the red phosphor to the YAG:Ce3+ phosphor resulted in an improved color rendering index (Ra) from 70 to 80. 相似文献