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1.
Single crystal of strontium iodide doped with 1% europium (SrI2:1% Eu2+) was grown by Vertical Gradient Freeze technique. UV excited emission spectra were studied as a function of temperature. Results indicate the thermal quenching of Eu2+ emission starts from ~400 K with a thermal activation energy of 0.39 eV. Gamma and UV excited decay measurements indicate that the scintillation decay time of SrI2:Eu2+ is longer than the lifetime of Eu2+ luminescence center in the SrI2 host. The thermoluminescence glow curve revealed a highly concentrated charge carrier trap at 50 K. Elimination of this trap is expected to enhance the energy migration of charge carriers and result in faster scintillation decay. 相似文献
2.
S. Omelkov V. Pustovarov M. Kirm I. Ogorodnikov L. Isaenko 《Radiation measurements》2010,45(3-6):292-294
This paper reports the results of a time-resolved photoluminescence and energy transfer processes study in Ce3+ doped SrAlF5 single crystals. Several Ce3+ centers emitting near 4 eV due to 5d-4f transitions of Ce3+ ions substituting for Sr2+ in non-equivalent lattice sites were identified. The lifetime of these transitions is in the range of 25–35 ns under intra-center excitation in the energy region of 4–7 eV at T = 10 K. An effective energy transfer from lattice defects to dopant ions was revealed in the – 7–11 eV energy range. Both direct and indirect excitation channels are efficient at room temperature. Excitons bound to dopants are revealed at T = 10 K under excitation in the fundamental absorption region above 11 eV, as well as radiative decay of self-trapped excitons resulting in luminescence near 3 eV. 相似文献
3.
Ruijin Yu Hongjuan Li Hailong Ma Caifeng Wang Huan Wang Byung Kee Moon Jung Hyun Jeong 《Journal of luminescence》2012,132(10):2783-2787
A thiogallate chalcogenide phosphor CaLaGa3S7:Eu2+ was synthesized by a solid-state reaction at 950 °C in a H2S atmosphere. The photoluminescence excitation,emission spectra, concentration quenching, fluorescence lifetime, and thermal quenching process of the phosphor were investigated in detail. It was found that the synthesized phosphor emitted intense and broadband yellowish-green light with a peak at 554 nm. Thus, the proposed phosphor is suitable for the development of blue or near UV LED. The critical dopant concentration of Eu2+ (Rc=15 Å) per unit formula was found to be 0.15 mol. At room temperature, the fluorescence lifetime of Eu2+ in CaLaGa3S7 was found to be 0.216 μs. The activation energy for thermal quenching was 0.29 eV. The chromaticity coordinates of our phosphor is very close in color to Y3Al5O12:Ce3+. Therefore, CaLaGa3S7:Eu2+ can be a good alternative as a yellowish-green phosphor and can be used for white light generation in phosphor-converted LEDs. 相似文献
4.
In this communication, we investigated the scintillation properties of Cs2LiGdCl6:10% Ce3+ single crystal. This scintillation crystal is grown by using the vertical Bridgman technique. X-rays induced emission spectra show that, Cs2LiGdCl6:10% Ce3+ emits into the Ce3+ band, spanning from 365 nm to 450 nm wavelengths. Under γ-ray excitation, the sample crystal shows three main decay time components of 129 ns (51%), 573 ns (32%) and 8.9 μs (17%). It offers an energy resolution of 5.0% (FWHM) for the 662 keV full absorption peak at room temperature. We measured an absolute light yield of 20,000 photons/MeV of absorbed γ-ray energy. We found that with a little exposure to the air, the scintillation properties of the Cs2LiGdCl6:10% Ce3+ crystal deteriorate, which is attributed to the highly hygroscopic nature of this material. We believe that the Cs2LiGdCl6:10% Ce3+ crystal can be a promising material for medical imaging and radiation detection. Moreover due to the presence of Li and Gd constituents, this scintillation crystal can also be the possible candidate for thermal neutron detection. 相似文献
5.
Yetta Eagleman Marvin Weber Anurag Chaudhry Stephen Derenzo 《Journal of luminescence》2012,132(11):2889-2896
X-ray excited emission spectra, photoluminescence excitation and emission spectra, optical reflectivity spectra, and pulsed X-ray and optical excited luminescence decay measurements are reported for cerium-doped La2Hf2O7 powders prepared by solid state synthesis. A broad luminescence associated with oxygen vacancies is observed in the region 350–750 nm with a peak around 460 nm. The photoluminescence spectra and the number of oxygen vacancies vary for samples annealed in oxidizing or reducing atmospheres and with the temperature of the synthesis process. Increasing the cerium concentration reduces the oxygen-vacancy-related emission due to the presence of Ce4+. First principles calculations predict that Ce4+ can substitute in Hf sites; this is confirmed from the optical reflectivity spectrum of cerium-doped La2Hf2O7. Photoluminescence excitation and emission spectra characteristic of Ce4+ charge transfer transitions and possibly Ce3+ are also observed. Although trivalent cerium may be present, no emission observed from cerium-doped La2Hf2O7 can be attributed to Ce3+ in La sites. 相似文献
6.
Luminescence and scintillation properties of newly discovered bromo-elpasolites Cs2NaGdBr6: Ce3+ (CNGB: Ce3+) are presented. Single crystals of CNGB: Ce3+ with dimensions up to Ø7×10 mm3 are successfully grown by the Bridgman technique. X-ray excited luminescence measurements of the grown samples showed a broad emission band in the wavelength range from 365 to 470 nm. It offered an energy resolution of 5.1% (FWHM) at 662 keV for 10% Ce sample. The light output of the investigated samples increases along with cerium concentration. A maximum light yield of ~36,800 ph/MeV is measured for the 10% Ce sample crystal. Under γ-ray excitation, CNGB: Ce3+ crystals showed three exponential decay time components. The scintillation mechanism in the sample crystal is presented. 相似文献
7.
The photoluminescence of zinc metaphosphate glasses activated by Dy3+, Ce3+/Dy3+ and Ce3+/Dy3+/Mn2+ ions was investigated. Non-radiative energy transfers from Ce3+ to Dy3+ and Ce3+ to Mn2+ are observed upon 280 nm excitation. The non-radiative nature of these transfers is inferred from the increase in the decay rate of the Ce3+ emission when the glass is co-doped with Dy3+ or Dy3+/Mn2+. It is demonstrated that zinc metaphosphate glasses can generate cold or warm white light emission when they are doped with Ce3+/Dy3+ or Ce3+/Dy3+/Mn2+ and pumped at 280 nm (peak emission wavelength of AlGaN-based LEDs). The CIE1931 chromaticity coordinates and color temperature were (0.34, 0.35) and 5250 K for the cold light, and (0.47, 0.43) and 2700 K for the warm light. 相似文献
8.
Here we reported photoluminescence properties of Eu2+ activated in novel and existing MgXAl10O17 (X = Sr, Ca) phosphor which has been prepared by combustion synthesis at 550 °C under UV and near UV excitation wavelength. The PL emission properties of MgSrAl10O17:Eu2+ were monitored at 254 nm and 354 nm respectively keeping emission wavelength at 469 nm. Whereas novel MgCaAl10O17:Eu2+ exhibit emission band at 452 nm keeping excitation at 378 nm. These blue emission corresponds to 4f65d1 → 4f7 transition of Eu2+ ions. Further phosphor was analyzed by XRD for the confirmation of desired phase and purity. 相似文献
9.
A novel Sr2SiO4:Eu (1–5 mol %) superstructures (SS) were synthesized using bio-sacrificial A.V. gel assisted ultrasound method. Powder X-ray diffraction patterns confirmed the presence of both α and β phase formation. It was evident that the morphological growth was highly reliant on A.V. gel concentration, sonication time, pH and sonication power. The formation mechanisms for different hierarchical SS were proposed. From diffuse reflectance spectra, the energy band gap was estimated and found to be ∼4.70–5.11 eV. The photoluminescence emission spectra for the excitation at 392 nm, shows characteristic emission peaks at 593, 613, 654 and 702 nm which were attributed to 5D0 → 7F0, 7F1, 7F2 and 7F3 transitions of Eu3+ ions respectively. Conversely, when the samples were subjected to the heat treatment at 850 °C for 3 h under argon atmosphere, display an intense broad emission peak with two de-convoluted peaks at 490 and 550 nm due to 4f65d1→4f1 (8S7/2) transitions of Eu2+ ions. The concentration quenching phenomenon was discussed which attributes to energy transfer, electron–phonon coupling and ion–ion interaction. The Judd–Ofelt intensity parameters and other radiative properties were estimated by using emission spectra. The CIE chromaticity coordinate values of Sr2SiO4:Eu2+ and Eu3+ nanophosphors were located in green and red regions respectively. The calculated CCT and CRI values specify that the present phosphor can be fairly useful for both green and red components of white LED’s. Luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting diodes. Overall, the results elucidated a rapid, environmentally benign, cost-effective and convenient method for Sr2SiO4:Eu3+ synthesis and for the possible applications such as solid state lighting and display devices. 相似文献
10.
Eu2+–Mg2+ co-doped alon phosphors were successfully prepared by carbothermal reaction at 1600 °C for 2 h and their structure and photoluminescence properties were studied. The lattice parameter increased with increasing Eu concentration, indicating the incorporation of Eu into alon crystal lattice. The pure alon phase was obtained when Eu concentration is below 0.2%. Compared with solid state reaction process, this method lead to less amounts of secondary phase, larger amounts of Eu2+ against Eu3+, smaller particle size, narrower particle size distribution and stronger luminescence intensity. The absolute emission intensity of obtained phosphor reached 82% relative to that of famous BAM: Eu2+ phosphor. The emission could be tuned widely from blue to green by varying carbon content. 相似文献
11.
I.N. Ogorodnikov V.A. Pustovarov S.A. Yakovlev L.I. Isaenko S.A. Zhurkov 《Journal of luminescence》2012,132(7):1632-1638
We report the results of complex study of luminescence and dynamics of electronic excitations in K2Al2B2O7 (KABO) crystals obtained using low-temperature luminescence-optical vacuum ultraviolet spectroscopy with sub-nanosecond time resolution under selective photoexcitation with synchrotron radiation. The paper discusses the decay kinetics of photoluminescence (PL), the time-resolved PL emission spectra (1.2–6.2 eV), the time-resolved PL excitation spectra and the reflection spectra (3.7–21 eV) measured at 7 K. On the basis of the obtained results three absorption peaks at 4.7, 5.8 and 6.5 eV were detected and assigned to charge-transfer absorption from O2? to Fe3+ ions; the intrinsic PL band at 3.28 eV was revealed and attributed to radiative annihilation of self-trapped excitons, the defect luminescence bands at 2.68 and 3.54 eV were separated; the strong PL band at 1.72 eV was revealed and attributed to a radiative transition in Fe3+ ion. 相似文献
12.
W. González E. Álvarez R. Martínez-Martínez E. Yescas-Mendoza I. Camarillo U. Caldiño 《Journal of luminescence》2012,132(8):2130-2134
The photoluminescence of a CeCl3, DyCl3 and MnCl2 doped aluminum oxide film deposited by ultrasonic spray pyrolysis was characterized by excitation, emission and decay time spectroscopy. A nonradiative energy transfer from Ce3+ to Dy3+ and Mn2+ is observed upon UV excitation at 278 nm (peak emission wavelength of AlGaN-based LEDs). Such energy transfer leads to a simultaneous emission of these ions in the blue, green, yellow and red regions, resulting in white light emission with CIE1931 chromaticity coordinates, x=0.34 and y=0.23, which correspond to cold white light with a color temperature of 4900 K. 相似文献
13.
Kwangwon Park Jaebum Lee Jehong Park Jongsu Kim Patrick Kung Seongsin M. Kim Gawngchul Kim 《Journal of luminescence》2010,130(12):2442-2445
Hexagonal Ba1.20Ca0.8?2x?ySiO4:xCe3+,xLi+,yMn2+ phosphors exhibit two emission bands peaking near 400 and 600 nm from the allowed f–d transition of Ce3+ ions and the forbidden 4T1–6A1 transition of Mn2+ ions, respectively. The strong interaction between Ce3+/Mn2+ ions is investigated in terms of energy transfer, crystal field effect, and microstructure by varying their concentrations. They show a higher quenching temperature of 250 °C than that of a commercially used (Ba,Sr)2SiO4:Eu2+ phosphor (150 °C). Finally, mixtures of these phosphors with green-emissive Ba1.20Ca0.70SiO4:0.10Eu2+ are tested and yielded correlated color temperatures from 3500 to 7000 K, and color rendering indices up to 95%. 相似文献
14.
Qian Wang Degang Deng Youjie Hua Lihui Huang Huanping Wang Shilong Zhao Guohua Jia Chenxia Li Shiqing Xu 《Journal of luminescence》2012,132(2):434-438
A novel Ce3+/Eu2+ co-activated LiSr4(BO3)3 phosphor has been synthesized by traditional solid-state reaction. The samples could display varied color emission from blue towards white and ultimately to yellow under the excitation of ultraviolet (UV) light with the appropriate adjustment of the relative proportion of Ce3+/Eu2+. The resonance-type energy transfer mechanism from Ce3+ to Eu2+ in LiSr4(BO3)3:Ce3+, Eu2+ phosphors is dominant by electric dipole–dipole interaction, and the critical distance is calculated to be about 29.14 Å by the spectra overlap method. White light was observed from LiSr4(BO3)3:mCe3+, nEu2+ phosphors with chromaticity coordinates (0.34, 0.30) upon 350 nm excitation. The LiSr4(BO3)3:Ce3+, Eu2+ phosphor has potential applications as an UV radiation-converting phosphor for white light-emitting diodes. 相似文献
15.
The red-emitting phosphor In2(MoO4)3:Eu3+ with cubic crystal structure was synthesized by a conventional solid-state reaction technique and its photoluminescence properties were investigated. The prepared phosphor can be efficiently excited by ultraviolet (395 nm) and blue (466 nm) light. The emission spectra of the phosphor manifest intensive red-emitting lines at 612 nm due to the electric dipole 5D0→7F2 transitions of Eu3+. The chromaticity coordinates of x=0.63, y=0.35 (λex=395 nm) and x=0.60, y=0.38 (λex=466 nm) are close to the standard of National Television Standard Committee values (NTSC) values. The concentration quenching of In2(MoO4)3:Eu3+ is 40 mol% and the concentration self-quenching mechanism under 466 nm excitation was the dd intereaction. As a result of the strong emission intensity and good excitation, the phosphor In2(MoO4)3:Eu3+ is regarded as a promising red-emitting conversion material for white LEDs. 相似文献
16.
S. Dhiren Meetei S. Dorendrajit Singh N. Shanta Singh V. Sudarsan R.S. Ningthoujam M. Tyagi S.C. Gadkari R. Tewari R.K. Vatsa 《Journal of luminescence》2012,132(2):537-544
White emitting nanocrystalline ZrO2:Eu3+ phosphors were synthesized by a simple precipitation route without using a capping agent. X-ray diffraction (XRD) study of ZrO2 and ZrO2:Eu3+samples revealed the presence of monoclinic and tetragonal phases. The monoclinic phase increases with increase in the annealing temperature while the tetragonal phase increases with increase in the concentration of Eu3+. This can be attributed to the presence of oxygen vacancy evolved when Zr4+ is replaced by Eu3+. Photoluminescence (PL) emission peaks of Eu3+ are observed at 591, 596, 606 and 613 nm on monitoring excitation wavelengths at 250, 286, 394 and 470 nm. The peaks at 591 and 606 nm were found to correlate with the tetragonal phase and those at 596 and 613 nm with the monoclinic phase. Intensities of these peaks are found to change as the crystal structure changes. The lifetime value corresponding to 591 nm peak increases with Eu3+ concentration at a particular heating temperature indicating increase of tetragonal phase with respect to monoclinic phase. The CIE co-ordinates of the doped samples were found to be close to that of white color (0.33, 0.33). The changes in the crystal structure of the doped samples due to doping and annealing did not affect the white color emission. 相似文献
17.
J. Matharu G. Cabailh R. Lindsay C.L. Pang D.C. Grinter T. Skála G. Thornton 《Surface science》2011,605(11-12):1062-1066
Local defects present in CeO2 ? x films result in a mixture of Ce3+ and Ce4+ oxidation states. Previous studies of the Ce 3d region with XPS have shown that depositing metal nanoparticles on ceria films causes further reduction, with an increase in Ce3+ concentration. Here, we compare the use of XPS and resonant photoemission spectroscopy (RESPES) to estimate the concentration of Ce3+ and Ce4+ in CeO2 ? x films grown on Pt (111), and the variation of this concentration as a function of Pd deposition. Due to the nature of the electronic structure of CeO2 ? x, resonant peaks are observed for the 4d–4f transitions when the photon energy matches the resonant energy; (hν = 121.0 eV) for Ce3+ and (hν = 124.5 eV) for Ce4+. This results in two discrete resonant photoemission peaks in valence band spectra. The ratio of the difference of these peaks with off-resonance scans gives an indication of the relative contribution of Ce3+. Results from RESPES indicate reduction of CeO2 ? x on deposition of Pd, confirming earlier findings from XPS studies. 相似文献
18.
Guoyi Dong Hengxin Ma Yufeng Liu Zhiping Yang Qingbo Liu 《Optics Communications》2012,285(20):4097-4101
A series of orange reddish emitting phosphors Eu3+-doped Sr3Bi(PO4)3 have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr3Bi(PO4)3:Eu3+ phosphors invariably exhibit five peaks assigned to the 5D0→7FJ (J=0, 1, 2, 3, 4) transitions of Eu3+ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu3+ content and the emission reached the maximum intensity at x=0.05 in Sr3Bi(PO4)3:xEu3+. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu3+-doped Sr3Bi(PO4)3 phosphors are promising orange reddish-emitting phosphors pumped by near-UV light. 相似文献
19.
Yu-qiang Zhang Xue-jian Liu Zheng-ren Huang Jian Chen Yan Yang 《Journal of luminescence》2012,132(10):2561-2565
Eu2+–Mn2+ codoped Ca-α-SiAlON phosphors, Ca0.736?ySi9.6Al2.4O0.8N15.2:0.064 Eu2+, yMn2+, were firstly synthesized by the high temperature solid state reaction method. The effects of doped Eu2+ and Eu2+–Mn2+ concentrations on the photoluminescence properties of the as-prepared phosphors were investigated systematically. Powder X-ray diffraction shows that pure Ca-α-SiAlON phase is synthesized after sintering at 1700 °C for 2 h under 0.5 MPa N2 atmosphere. The excitation spectra of Eu2+-doped Ca-α-SiAlON phosphors are characterized by two dominant bands centered at 286 nm and 395 nm, respectively. The photoluminescent spectrum of Eu2+-doped Ca-α-SiAlON phosphor exhibits an intense emission band centered at 580 nm due to the allowed 4f 65d→4f 7 transition of Eu2+, showing that the phosphor is a good candidate for creating white light when coupled to a blue LED chip. The intensities of both excitation and emission spectra monotonously decrease with the increment of codoped Mn2+ content (i.e. y value), indicating that energy transfer between Eu2+ and Mn2+ is inefficient in the case of Eu2+–Mn2+ codoped Ca-α-SiAlON phosphors. 相似文献
20.
Fengjiao Qian Renli Fu Simeon Agathopoulos Xiguang Gu Xiufeng Song 《Journal of luminescence》2012,132(1):71-75
Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603 nm, a full width at half maximum of 110 nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01 mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ~31 Å. 相似文献