共查询到20条相似文献,搜索用时 13 毫秒
1.
Paramita Saha Chowdhury 《Journal of luminescence》2007,124(2):327-332
Here, we have examined the role of capping agent on the optical properties of CdS nanoparticles by steady-state and time-resolved photoluminescence (PL) spectroscopy. The estimated particles sizes are 3.45, 2.5 and 2.39 nm for uncapped, capped with silica (SiO2) and thiosalicylic acid (TSA), respectively. The absorption and emission spectra show a clear blue shift to shorter wavelengths in presence of TSA- and SiO2-capped nanoparticles. It is found that the average decay time 〈τ〉 are 6.24, 4.54 and 2.84 ns for uncapped, capped with SiO2 and TSA nanoparticles, respectively. Our analysis suggests that the hole or the electron is trapped on thiol molecule of TSA or hydroxyl group of SiO2, then radiative recombination of the electron and hole is delayed, resulting in strong quenching of PL efficiency. 相似文献
2.
Paramita Saha Chowdhury 《Solid State Communications》2004,131(12):785-788
The emission intensity of the peak at 612 nm (5D0→7F2) of the Eu3+ ions activated SnO2 nanocrystals (doped and coated) is found to be sensitive to the nanoenvironment. We have compared the luminescence efficiencies of the nanocrystals of SnO2 doped by Eu2O3 with those of SnO2 coated by Eu2O3 and we found that the intensities are significantly higher in coated nanocrystals. Furthermore, it is clear from luminescence intensity measurements that Eu3+ ions occupy low symmetry sites in the Eu2O3 coated SnO2 nanocrystal. The analysis suggests that the radiative relaxation rate is higher in Eu2O3 coated SnO2 nanocrystals than Eu2O3 doped SnO2 nanocrystals due to the asymmetric environment of Eu3+ ions in coated samples. 相似文献
3.
Hsu-Cheng Hsu 《Solid State Communications》2004,131(6):371-375
The coupling strength of the radiative transition of hexagonal ZnO nanowires to the longitudinal optic (LO) phonon polarization field is deduced from temperature dependent photoluminescence spectra. An excitonic polaron formation is discussed to explain why the interaction of free excitons with LO phonons in ZnO nanowires is much stronger than that of bound excitons with LO phonons. The strong exciton-phonon coupling in ZnO nanowires affects not only the Haung-Ray S factor but also the FXA-1LO phonon energy spacing, which can be explained by the excitonic polaron formation. 相似文献
4.
Liu Huangqing Wang Lingling Chen Shuguang Zou Bingsuo Peng Zhiwei 《Applied Surface Science》2007,253(8):3872-3876
Effect of annealing temperature on luminescence of Eu3+ ions was studied in nanocrystal zirconia prepared by co-precipitation. The XRDs reveal with annealing temperature increasing the tetragonal crystal phase of the samples is stable. The emission spectra show the strong emission at 595 and 604 nm at 394 nm excitation. Under continuous UV (394 nm) irradiation the 604 nm emission intensity changes of the samples show as a function of irradiation time. In addition, the charge-transfer states of the samples are affected by the annealing temperature. These are associated with the defects at/in the surface of the nanocrystalline ZrO2 with Eu3+ ions. 相似文献
5.
Qiang Wang Daocheng Pan Xiangling Ji Lijia An Bingzheng Jiang 《Journal of luminescence》2006,118(1):91-98
A new solvothermal route has been developed for synthesizing the size-controlled CdSe nanocrystals with relatively narrow size distribution, and the photoluminescence (PL) quantum yields (QYs) of the nanocrystals can reach 5-10%. Then the obtained CdSe nanocrystals served as cores to prepare the core/shell CdSe/CdS nanocrystals via a two-phase thermal approach, which exhibited much higher PL QYs (up to 18-40%) than the CdSe core nanocrystals. The nanocrystal samples were characterized by ultraviolet-visible (UV-vis) absorption spectra, PL spectra, wide-angle X-ray diffraction (WAXD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). 相似文献
6.
S.V. Bhat 《Solid State Communications》2007,141(6):325-328
Indium-doped GaN nanocrystals with 5% and 10% In have been prepared by a low temperature solvothermal method using hexamethyldisilazane as the nitriding reagent. The nanocrystals show Raman bands at lower frequencies compared to GaN. Photoluminescence spectra of the In-doped GaN nanocrystals exhibit an increase in the FWHM with the decrease in the PL band energy, the band energy itself decreasing with increase in the In content. 相似文献
7.
Yttrium oxysulfide doped with europium (Y2O2S:Eu3+) red phosphor is used in UV light emitting diodes (LEDs) by mixing with blue and green phosphors to generate white light which are important for the application in general lighting. Here, we demonstrate the effect of shape and size and the concentration of activator (Eu) of red Y2O2S phosphor. 相似文献
8.
B.M. Monroy J. Aguilar-Hernández J. Fandiño G. Contreras-Puente J.C. Alonso 《Journal of luminescence》2006,121(2):349-352
Very thin (nanometric) silicon layers were grown in between silicon nitride barriers by SiH2Cl2/H2/NH3 plasma-enhanced chemical vapor deposition (PECVD). The multilayer structures were deposited onto fused silica and silicon substrates. Deposition conditions were selected to favor Si cluster formation of different sizes in between the barriers of silicon nitride. The samples were thermally treated in an inert atmosphere for 1 h at 500 °C for dehydrogenation. Room-temperature photoluminescence (RT-PL) and optical transmission in different ranges were used to evaluate the optical properties of the structures. UV-VIS absorption spectra present two band edges. These band edges are well fitted by the Tauc model typically used for amorphous materials. RT-PL spectra are characterized by strong broad bands, which have a blue shift as a function of the deposition time of the silicon layer, even for as-grown samples. The broad luminescence could be associated with the confinement effect in the silicon clusters. After annealing of the samples, the PL bands red shift. This is probably due to the thermal decomposition of N-H bonds with further effusion of hydrogen and better nitrogen passivation of the nc-Si/SiNx interfaces. 相似文献
9.
A series of Er3+/Yb3+-co-doped 60Bi2O3-(40−x) B2O3 -xGa2O3 (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er3+:4I13/2 level and thermal stability were measured and investigated. Three Judd-Ofelt intensity parameters Ωt (t=2,4,6) (Ω2=(4.67-5.93)×10−20 cm2, Ω4=(1.50-1.81)×10−20 cm2, Ω6=(0.92-1.17)×10−20 cm2) of Er3+ ions were calculated by Judd-Ofelt theory. It is found that the Ω6 first increases with the increase of Ga2O3 content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section () of Er3+: 4I13/2→4I15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69-76 nm) of the 4I13/2→4I15/2 transition of Er3+ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers. 相似文献
10.
Sixfold symmetrical Mg-doped CdS nanowires have been fabricated through high temperature vapor-solid deposition process. The experimental study of the temperature-dependent photoluminescence properties of the Mg-doped CdS nanowires from 10 K to 300 K was reported. The Mg-doped CdS nanowires show intensive cyan-color light emission properties from 10 K to 200 K. The results indicate that there are two strong peaks situated at the green emission (at 528 nm) and red emission (at 655-695 nm), and two weak UV emission peaks at 378 nm and 417 nm, respectively. The ratio of green to red emission was decreased with temperature increased. When the temperature is above 200 K, the orange-color light was observed from the Mg-doped CdS nanowires. Therefore, the intensive emission properties of the Mg-doped CdS nanowires have a great potential for use as nanoscaled optoelectronic intensive light emitters under different temperature. 相似文献
11.
Nanosized ZnGa2O4:Cr3+ powder is synthesized through hydrothermal method. The average particle size is 20 nm and they are spherical in shape. The excitation band from the charge transfer between Cr3+-O2− shows a blueshift behavior due to quantum confinement effect. X-ray diffraction pattern, Fourier transform-infrared spectrum, and electron paramagnetic resonance signal indicate that nanosized ZnGa2O4:Cr3+ phosphor shows many defect-related energy states and heavy lattice distortion in comparison with bulk ZnGa2O4:Cr3+ phosphor. Many defect states result in more nonradiative loss and shorter decay time. 相似文献
12.
Lingli Wang 《Journal of luminescence》2007,126(1):160-164
The luminescent properties of CaYBO4:Ln(Ln=Eu3+, Tb3+) were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) region. The CT band of Eu3+ at about 245 nm blue-shifted to 230 nm in VUV excitation spectrum; the band with the maximum at 183 nm was considered as the host lattice absorption. For the sample of CaYBO4:0.08Tb3+, the bands at about 235 and 263 nm were assigned to the f-d transitions of Tb3+ and the CT band of Tb3+ was calculated according to Jφrgensen's theory. Under UV and VUV excitation, the main emission of Eu3+ corresponding to the 5D0-7F2 transition located at about 610 nm and two intense emission of Tb3+ from the 5D4-7F5 transition had been observed at about 542 and 552 nm, respectively. With the incorporation of Gd3+ into the host lattice of CaYBO4, the luminescence of Tb3+ was enhanced while that of Eu3+ was decreased because of their different excitation mechanism. 相似文献
13.
Shixun Dai Chunlei Yu Gang Zhou Junjie Zhang Guonian Wang Lili Hu 《Journal of luminescence》2006,117(1):39-45
Er2O3-doped TeO2-ZnO-La2O3 modified tellurite glasses were prepared by the conventional melt-quenching method, and the Er3+: 4I13/2→4I15/2 fluorescence properties have been studied for different Er3+ concentrations. Infrared spectra were measured in order to estimate the exact content of OH− groups in samples. Based on the electric dipole-dipole interaction theory, the interaction parameter, CEr,Er, for the migration rate of Er3+: 4I13/2→4I13/2 in modified tellurite glass was calculated. Finally, the concentration quenching mechanism using a model based on energy transfer and quenching by hydroxyl (OH−) groups was presented. 相似文献
14.
This paper reports the photoluminescence (PL) properties of nanocrystalline YVO4: Tm phosphor synthesized by the polymerizable complex method based on the Pechini-type reaction. The powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption spectroscopy and PL. The results of XRD and TEM show that, high-quality nanopowders with controlled morphology and microstructure were prepared at a relatively low temperature about 700 °C. Upon ultra violet excitation the vanadate host transferred energy to thulium ions efficiently and strong blue emission (475 nm) assigned to 1G4→3H6 transmission is observed. By analyzing excitation and emission spectra of thulium doped yttrium vanadate, we deduced the mechanism of the energy transfer between vanadate host and thulium ions. 相似文献
15.
We have synthesized blue-emitting CaMgSi2O6:Eu2+ (CMS) and evaluated its thermal stability after baking process. To evaluate its thermal stability, CMS was baked in air at 500 and 600 °C for 20 min, respectively, and compared with BaMgAl10O17:Eu2+ (BAM) treated in the same condition. After baking process, CMS showed somewhat increased photoluminescence (PL) intensity with baking temperature. To investigate the reasons behind the increase of PL intensity after baking process, vacuum ultraviolet (VUV)/PL, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) techniques were applied. From the ESR and the XPS analyses, it is noted that spectral intensity of Eu2+ ion somewhat increased. It was believed that due to charge balance Eu3+ ions reduced to Eu2+ ions during the baking process in air. It is clear that the concentration of Eu2+ increased after the baking process in air and it leads to slight increase of the VUV/PL intensity of CMS phosphor. 相似文献
16.
The CdSe nanocrystals with different sizes were synthesized in aqueous solution through water-sol method using l-cysteine hydrochloride as the stabilizer. The pH-dependent optical properties of the CdSe nanocrystals were investigated. Furthermore, the CdSe nanocrystals were dispersed into chloroform by using a cationic surfactant, and mixed with poly(N-vinylcarbazole) (PVK) in different mass ratios. The investigation of the photoluminescence (PL) and absorption spectra of the CdSe:PVK blends suggested that energy transfer from the PVK excited states to the CdSe nanocrystals, and it is more efficient for the smaller size nanocrystals. In the meantime, it was found that the relative emission intensity of the CdSe nanocrystals to PVK in the blends depended on the mass ratios, and the emission from the CdSe nanocrystals was the strongest as the mass ratio of CdSe to PVK was 2:1. 相似文献
17.
Jong Hyuk Kang Won Bin Im Jin Young Kim Yun Chan Kang 《Solid State Communications》2005,133(10):651-656
We have studied the photoluminescence (PL) of (Y, Ln)VO4:Eu3+ (Ln=La and Gd) phosphors and the correlation of the PL of those phosphor with their crystal structure. It is found that (Y, Gd)VO4:Eu3+ phosphors have the same crystal structure as YVO4:Eu3+, which is tetragonal with a little different lattice parameters. In the case of (Y, La)VO4:Eu3+ phosphors, however, the gradual change from tetragonal to monoclinic structure of host lattice was observed as the amount of La ion increased. To investigate the PL property of (Y, Ln)VO4:Eu3+ (Ln=La and Gd) phosphors, vacuum ultraviolet (VUV) and ultraviolet (UV) excitation were used. The favorable crystal structure for the PL intensity of orthovanadate phosphor under 147 and 254 nm excitation was tetragonal containing Gd ion and under 365 nm excitation was monoclinic containing La ion which might have the lowest site symmetry for Eu3+ ion. 相似文献
18.
We report on the reactive electron beam evaporative growth of well-aligned ZnO nanocolumns on Si (001) wafers in the environment of NH3/H2 gas mixture by using polycrystalline ZnO ceramic target as source material. The growth was carried out at low temperatures (400-450 °C) without employing any metal catalysts. Field emission scanning electron microscopy (FESEM) revealed that nanocolumns with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates and terminated by smooth hexagonal (0001) facets with no terrace-like steps emerged, which should render potential applications such as inherent resonance cavities in fabricating ultraviolet-laser arrays. X-ray diffraction measurements revealed that ZnO nanocolumns were highly c-axis oriented, which is well consistent with the FESEM observations. More importantly, photoluminescence investigations of the nanocolumns demonstrated the strong excitonic emission and extremely weak deep level emission, indicating the high crystalloid and optical quality of the nanocolumns. 相似文献
19.
The thermo-luminescence (TL) of rare earth ions RE3+ (RE=Ln, excluding Pm, Eu and Lu) co-doped phosphors CaGa2S4:Eu2+, RE3+ was studied between room temperature and 300 °C, and 3D thermo-luminescence of the phosphors were measured from room temperature to 400 °C. The basic material CaGa2S4:Eu2+, showed at least two bands in the TL glow curve. Changing the auxiliary activator RE3+ (rare earth ion), intensities and the positions of the TL glow curve peaks were affected significantly. For the phosphors with long afterglow, auxiliary activator such as Ce3+, Pr3+, Gd3+, Tb3+, Ho3+, or Y3+ created some new defects in these compounds at lower trap levels and enhanced their TL intensities. The Nd3+ or Er3+ auxiliary activator only enhanced TL intensities to a low extent, so these two phosphors have short persistent luminescence at room temperature. TL intensities of La3+, Sm3+, Tm3+ or Yb3+ co-doped phosphors were suppressed greatly and no afterglow was shown. The relationship between auxiliary activators and corresponding thermo-luminescence curves of phosphors CaGa2S4:Eu2+, RE3+ are discussed in detail. According to our results, suitable activation energy and enough high corresponding trap density are necessary for the phosphor with long afterglow. 相似文献
20.
Luminescent properties of Pr3+ or Mn2+ singly doped and Pr3+, Mn2+ co-doped LaMgB5O10 are investigated by synchrotron radiation VUV light. When LaMgB5O10:Pr3+ is excited at185 nm, the photon cascade emission between 4f levels of Pr3+ is observed. In the excitation spectra of LaMgB5O10:Mn2+ monitoring the 615 nm emission of Mn2+, several excitation bands in a spectral range from 330 to 580 nm are recorded, among which the most intense band is centered at 412 nm (6A1g→4Eg-4A1g). This band has considerable spectra overlap with the 410 nm emission (1S0→1I6) of Pr3+, which is favorable for energy transfer from Pr3+ to Mn2+. Such energy transfer is observed in the co-doped sample, converting the violet emission (410 nm) of Pr3+ into the red emission (615 nm) of Mn2+. The concentration dependence of transfer efficiency is also investigated. 相似文献