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1.
CaxSr1 − xAl2O4: Eu2+ photoluminescent materials with high brightness and long afterglow were in situ synthesized by hybrid precursor assembly sol-gel technology in a reductive atmosphere. The particle size of luminescent materials is in the range of 30-60 nm by the estimation of XRD. And SEM shows that there exists uniform morphology and microstructure owing to the hybrid precursors. The influence of co-doping Ca2+ and Sr2+ on the luminescence of the phosphor was studied. Their excitation and emission spectra were very similar to that of SrAl2O4: Eu2+ phosphors and all of them have long afterglow phenomenon. Changing the co-doping concentrations of Ca2+ and Sr2+ in CaxSr1 − xAl2O4: Eu2+ phosphors, the luminescent intensities are different. When the proportion of Ca and Sr is 6 to 4, the phosphor reaches the strongest emitting intensity. 相似文献
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3.
BaSi2O2N2: Eu2+ is an efficient phosphor because of its high quantum yield and quenching temperature. Partial substitution of Ba2+ by Sr2+ is the most promising approach to tune the color of phosphors. In this study, a series of (Ba1−x−ySrxEuy)Si2O2N2 (x = 0.0–0.97, y = 0.00–0.10) phosphors are synthesized via high-temperature solid-state reactions. Intense green to yellow phosphors can be obtained by the partial substitution of the host lattice cation Ba2+ by either Sr2+ or Eu2+. The luminescent properties and the relationships among the lowest 5d absorption bands, Stokes shifts, centroid shifts, and the splitting of Eu2+ are studied systematically. Then, based on (Ba1−x−ySrxEuy)Si2O2N2 phosphors and near-ultraviolet (∼395 nm)/blue (460 nm) InGaN chips, intense green–yellow light emitting diodes (LEDs) and white LEDs are fabricated. (Ba0.37Sr0.60)Si2O2N2: 0.03Eu2+ phosphors present the highest efficiency, and the luminous efficiency of white LEDs can reach 17 lm/w. These results indicate that (Ba1−x−ySrxEuy)Si2O2N2 phosphors are promising candidates for solid-state lighting. 相似文献
4.
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
5.
(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
6.
(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
7.
Ba1−ySryLa4−xTbx(WO4)7 (x = 0.02-1.2, y = 0-0.4) phosphors were prepared via a solid-state reaction and their photoluminescence properties were investigated. An analysis of the decay behavior indicates that the energy migration between Tb3+ ions is conspicuous in the 5D3 → 7F4 transition due to the cross-relaxation in BaLa4(WO4)7. A partial substitution of Ba2+ by Sr2+ can not only enhance the emission intensity but also increase the solid solubility of Tb3+ in Ba1−ySryLa4−xTbx(WO4)7. The emission intensity of the 5D4 → 7FJ (J = 4, 5, 6) transitions can be enhanced by increasing Sr2+ and Tb3+ concentrations, with the optimal conditions being x = 1.2, y = 0.4 (Ba0.6Sr0.4La2.8Tb1.2(WO4)7). Under near-UV excitation at 379 nm, the CIE color coordinates of Ba1−ySryLa4−xTbx(WO4)7 vary from blue (0.212, 0.181) at x = 0.04, y = 0, to green (0.245, 0.607) at x = 1.2, y = 0.4. 相似文献
8.
151Eu-Mössbauer spectroscopic and powder X-ray diffraction (XRD) study has been performed for the EuyM1−yO2−x (M = Th and U) systems over the entire composition range of 0 ≤ y ≤ 1.0. The XRD results of the Eu-Th system showed that a very wide defect-fluorite (DF) type phase in which oxygen vacancies (VO) are disordered (x = y/2) is formed for 0 ≤ y < 0.5 and that two-phase regions sandwitching a narrow C-type (C) single phase around y ≈ 0.8 appear for 0.5 < y < 0.8 (DF + C) and 0.82 < y < 1.0 (C + B-type (monoclinic) Eu2O3). The Mössbauer results show that the isomer shifts (ISs) of Eu3+ in this system smoothly increase with Eu composition, y. The decrease of average coordination number (CN) of O2− around Eu3+ with increasing y (CN = 8 − 2y) (x = y/2) results in the decrease of the average EuO bond length, which is due to the decrease of repulsion force between O2− anions. This result confirms that the IS of Eu3+ correlates well with the average EuO bond length in oxide systems. For the Eu-U system, the lattice parameter, a0, of the system decreases almost linearly with y, in accordance with the calculated a0 versus y curve for the oxygen-stoichiometric (i.e. x = 0) fluorite-type dioxide (CN = 8). The ISs of Eu3+ in this composition range remain almost constant around 0.5 mm/s, which is comparable to those of pyrochlore oxides (Eu2Zr2O7 and Eu2Hf2O7 (y = 0.5)) with O2−-eight-fold coordinated Eu3+(CN = 8). 相似文献
9.
Hom Nath Luitel Takanori Watari Rumi Chand Toshio Torikai Mitsunori Yada Hiroshi Mizukami 《Materials Science and Engineering: B》2013,178(12):834-842
Color point tuning is an important challenge for improving the practical applications of various displays, especially there are very limited white color single hosts that emits in the white spectrum. In this paper, the possibility of color tuning by substituting part of host lattice cation (Sr2+ ions) by Ca2+ or Ba2+ ions in an efficient strontium aluminate phosphor, Sr4Al14O25:Eu2+,Dy3+, is reported and found to be very promising for displays. A detail study by replacing part of Sr2+ with Ca2+ or Ba2+ has been investigated. X-ray diffraction study showed that crystal structure of Sr4Al14O25 is preserved up to 20 mol of Ca2+ ion exchange while it is limited to 10 mol of Ba2+ ions exchange. Substantial shift in the emission band and color were observed by substitution of Sr2+ by Ca2+ or Ba2+ ions. A bluish-white emission and afterglow was observed at higher Ca2+ ions substitution. Further, partial Ca2+ substitutions (up to 0.8 mol) resulted in enhanced afterglow of Sr4Al14O25:Eu2+,Dy3+ phosphor. However, Ba2+ substitution decreased the fluorescence as well afterglow of the Sr4Al14O25:Eu2+,Dy3+ phosphor significantly. The enhanced phosphorescence by partial Ca2+ substitution is explained on the basis of increased density of shallow traps associated with higher solubility of Dy3+ ions in to the host lattice due to equivalent size of Ca2+ and Dy3+ ions. Thus, Ca2+ substitution in the Sr4Al14O25:Eu2+,Dy3+ phosphor is a promising method for tuning the emission color and improving the afterglow intensity of the phosphor. 相似文献
10.
The phosphors in the system Sr2−x−yP2O7:xEu2+,yMn2+ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have strong absorption in the near UV region, which is suitable for excitation of ultraviolet light emitting diodes (UVLEDs). The orange-reddish emission of Mn2+ in these phosphors can be used as a red component in the tri-color system and may be enhanced by adjusting the Mn2+/Eu2+ ratio. The energy transfer from Eu2+ to Mn2+ is observed with a transfer efficiency of ∼0.45 and a critical distance of ∼10 Å. The results reveal that Sr2−x−yP2O7:xEu2+,yMn2+ phosphors could be used in white light UVLEDs. 相似文献
11.
(Ca1 + x − yEuy)Ga2S4 + x phosphors have been synthesized one step by solid state reaction. The photoluminescence excitation and emission spectra of phosphors have been studied; the influence of host composition and Eu2+ concentration on emission spectra has also been investigated. The emission spectrum consists of yellow emission at 550 nm and red emission at 650 nm. It also indicates that the excitation spectrum is a broadband and can be well matched with the emission of GaN chip. Combined these phosphors with 460 nm-emitting GaN chips, White LEDs have been fabricated. Their electroluminescence spectra have been measured under 20 mA forward-bias current. Their CIE chromaticity coordinates and color temperature indicate that (Ca1 + x − yEuy)Ga2S4 + x phosphors are promising phosphors for GaN-based white LEDs. 相似文献
12.
Abanti Nag 《Materials Research Bulletin》2004,39(3):331-342
The role of B2O3 in realizing the long phosphorescence of Eu(II)+Dy(III) doped strontium aluminates has been investigated. IR and solid state MAS NMR spectra show the incorporation of boron as BO4 in the AlO4 framework of SrAl2O4 and Sr4Al14O25. Phosphor, made free of glassy phases by washing with hot acetic acid+glycerol, did not show any photoconductivity under UV irradiation, indicating that the mechanism involving hole conduction in valence band is untenable for long phosphorescence. EPR studies confirm the presence of both electron and hole trap centers. Dy3+ forms substitutional defect complex with borate; [Dy-BO4-VSr]2−, and acts as a hole trap center. The electron centers are formed by the oxygen vacancies associated with BO33−, i.e. [BO3-VO]3−. Under indigo light or near UV irradiation, the photoinduced electron centers are formed as [BO3-VO(e′)]4−. The holes are released from [Dy-BO4-VSr(h)]1− under thermal excitation at room temperature. The recombination of electrons with holes releases energy which is expended to excite Eu2+ to induce long phosphorescence. 相似文献
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The (Y0.94−x−yAlxGdyEu0.06)BO3 (0 ≤ x ≤ 0.04 and 0 ≤ y ≤0.4) phosphors were single-phase with a hexagonal vaterite crystal structure. The (Y0.94−x−yAlxGdyEu0.06)BO3 phosphor powders showed smooth, regular, and spherical morphology. The emission intensity of the Al- and Gd-co-doped (Y0.74−xAlxGd0.2Eu0.06)BO3 and (Y0.925−yAl0.015GdyEu0.06)BO3 phosphors was much higher than that of Al-free (Y0.74Gd0.2Eu0.06)BO3 and Gd-free (Y0.925Al0.015Eu0.06)BO3 phosphors, respectively. This means that the simultaneous addition of Gd and Al to yttrium borates was desirable for improving their photoluminescent properties. 相似文献
14.
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
15.
Sue Jin KimHyung Il Won Nersisyan HaykChang Whan Won Duk Young JeonArtavazd G. Kirakosyan 《Materials Science and Engineering: B》2011,176(18):1521-1525
A new composition of red strontium aluminate phosphor (Sr4Al2O7:Eu3+, Eu2+) is synthesized using a solid state reaction method in air and in a reducing atmosphere. The investigation of firing temperature indicates that a single phase of Sr4Al2O7 is formed when the firing temperature is higher than 1300 °C and that a Sr3Al2O6 phase is formed as the main peak below 1300 °C. The effects of firing temperature and doping concentration on luminescent properties are investigated. Sr4Al2O7 phosphors exhibit the typical red luminescent properties of Eu3+ and Eu2+. A comparison photoluminescence study with Sr3Al2O6 phosphor shows that Sr4Al2O7 has higher emission intensity than Sr3Al2O6 as a result of the higher optimum doping concentration of Sr4Al2O7 phosphor. 相似文献
16.
A.L. Shaula J.C. Waerenborgh E.V. Tsipis M.V. Patrakeev 《Materials Research Bulletin》2004,39(6):763-773
Increasing iron content in apatite-type La9.83Si4.5Al1.5−yFeyO26+δ (y=0.5-1.5) leads to increasing unit cell volume, fraction of Fe4+, partial oxygen ionic and p-type electronic conductivities, and ceramics sinterability. The oxygen ion transference numbers, determined by Faradaic efficiency (FE) measurements at 973-1223 K in air, are in the range 0.986-0.994. Data on total conductivity and Seebeck coefficient as functions of the oxygen partial pressure, varying in the range 10−2 Pa to 70 kPa, confirm that under oxidizing conditions the ionic conduction in Fe-substituted La9.83(Si,Al)6O26+δ apatites is dominant. Due to stabilization of Fe3+, substantially worse transport properties are observed for A-site stoichiometric La10Si4Fe2O26, having activation energy for ionic conductivity of 107 kJ/mol and electron transference numbers close to 0.03. The correlation between partial ionic and electron-hole conductivities suggests a significant role of Fe4+ formation compensated by extra oxygen incorporation into the vacant sites, which are formed due to Frenkel-type disorder induced by La vacancies. The average thermal expansion coefficients of Fe-doped La10−x(Si,Al)6O26+δ ceramics, calculated from dilatometric data in air, are 8.9×10−6 to 9.9×10−6 K−1 at 300-1250 K. 相似文献
17.
Kyurhee Shim 《Thin solid films》2008,516(10):3143-3146
The principal band gaps (E(Γ),E(L), and E(X)) and bond lengths (d(x,y,z))of the alloy (AlxGa1−x)1−zInzPyAs1−y (where, 0 < x + z < 1, and 0 < y < 1) are calculated over the entire composition range based on the first order correlated function expansion (CFE) scheme. Defining the lattice strain parameter as , it is found that a good quality of alloy (defining ? < ∼ 0.5%) can be obtained in the composition region : 0 < x < ∼ 0.3, 0 < y < ∼ 0.2 and 0 < z < ∼ 0.1. The first order CFE lattice matching relations and corresponding band gaps for the alloy on the GaAs substrate are also determined. It is found that the principal band gaps of the alloy (AlxGa1−x)1−zInzPyAs1−y lattice matched to GaAs covers band gap ranges: 1.45 eV E < (Γ) 2.69 eV, 1.80 eV < E(L) < 2.38 eV, and 1.97 eV < E(X) < 2.20 eV, while the direct band gap covers from 1.45 eV to 2.05 eV. Our theoretical prediction was compared with the existing experimental data. 相似文献
18.
SrLa1−xRExGa3O7 (RE = Eu3+, Tb3+) phosphor films were deposited on quartz glass substrates by a simple Pechini sol-gel method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy, field-emission scanning electron microscopy, photoluminescence spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 700 °C and crystallized fully at 900 °C. The results of FT-IR spectra were in agreement with those of XRD. Uniform and crack-free films annealed at 900 °C were obtained with average grain size of 80 nm, root mean square roughness of 46 nm and thickness of 130 nm. The RE ions showed their characteristic emission in crystalline SrLa1−xRExGa3O7 films, i.e., Eu3+5D0-7FJ (J = 0, 1, 2, 3, 4), Tb3+5D4-7FJ (J = 6, 5, 4, 3) emissions, respectively. The optimum concentrations (x) of Eu3+ and Tb3+ were determined to be 50, and 80 mol% in SrLa1−xRExGa3O7 films, respectively. 相似文献
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In this study, bulk ceramics with general formula Bi1−ySryFe(1−y)(1−x)Sc(1−y)xTiyO3 (x = 0-0.2, y = 0.1-0.3 mol%) were prepared by traditional solid-state reaction method. As a comparison, bulk BiFeO3 (BF) was also sintered by rapid sintering method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that apart from a small amount of secondary phase detected in BF, all other samples crystallized in pure perovskite structure and maintained original R3c space group. The room temperature M-H curves were obtained. While BF had a coercive magnetic field (Hc) of 150 Oe, Bi1−ySryFe1−yTiyO3 solid solutions had a much larger value (for y = 0.1, 0.2, 0.3, Hc were 4537, 5230 and 3578 Oe, respectively). Sc3+ substitution decreased the Hc values of these solid solutions remarkably, and resulted in soft magnetic properties, as well as a decrease of the dielectric loss. At 1 MHz, the tan δ of Bi0.7Sr0.3Fe0.7(1−x)Sc0.7xTi0.3O3 with x = 0.05, 0.1, 0.15, 0.2 were 0.1545, 0.1078, 0.1046 and 0.1701, respectively. 相似文献