摘要:A series of Ca2SiO4:0.01Ce3+,xSm3+,(0.01+x)Li+ (x=0~0.05) phosphors were synthesized under a weak reducing atmosphere by traditional solid state reactions. Photoluminescence and energy transfer (ET) properties were investigated in detail. When the mole fraction of Ce3+ was fixed at 1%, the sample of Ca2SiO4:0.01Ce3+,0.02Sm3+,0.03Li+ shows the highest red light emitting. Under 360 nm UV excitation, efficient Ce3+ to Sm3+ energy transfer was observed. The highest ET efficiency of Ce3+-Sm3+ is 55.8%. Based on Inokuti-Hirayama formula, the ET type of Ce3+ to Sm3+ was supposed to be dipole-dipole interaction. The critical distance of Ce3+ to Sm3+ was calculated to be about 0.55 nm.
摘要:The NaYF4:Yb3+,Tm3+ nanocrystals were synthetized with different doping concentrations of Yb3+, Tm3+ ions by a thermal decomposition method. The morphology, crystalline phase and optical properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and luminescent spectra.With the concentrations of Tm3+ increasing, the emission intensity of Tm3+ firstly increased and then decreased because of the effects of ion concentration quenching and cross relaxation between the neighboring Tm3+. The decrease of the luminescent intensity with the increase of Yb3+ ions is due to the concentration quenching effect.
摘要:Eu3+-doped KLa(MoO4)2 phosphor was prepared successfully via the hydrothermal process. And it was characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) and photoluminescence (PL), respectively. The experimental results indicate that the pH values of the reaction solution have important effects on the phase structures and the morphologies of the products. A crystallization pH value of 7 was optimal. This phosphor can be effectively excited by 279, 395, 465 nm and emits red light at 617 nm with line spectra. The optical properties suggest that KLa(MoO4)2:Eu3+ is an efficient red-emitting phosphor for white LEDs applications.
摘要:Tb3+ doped sodium gadolinium pyrosilicate phosphors Na3Gd1-xTbxSi2O7 were prepared using a high-temperature solid-state reaction technique. The spectroscopic properties of Na3Gd1-x-TbxSi2O7 in VUV-UV-Vis range and fluorescent lifetimes were investigated. The lowest 5d orbitals of Tb3+ in two sites both 6-fold distorted octahedron coordination (trigonal antiprism tap) (Gd3+(1)) and 6-fold regular trigonal prism coordination (tp) (Gd3+(2)) were discussed. The lowest 5d orbitals of Tb3+ in Gd3+(1) is 235 nm for allowed transition, and 280 nm for forbidden transition. The lowest 5d orbitals of Tb3+ in Gd3+(2) is 224 nm for allowed transition, and 256 nm for forbidden transition. The nonradiative energy-transfer rate K and energy-transfer efficiency η were also investigated. The results show that there is efficient Gd3+-Tb3+ energy-transfer in Na3Gd1-xTbxSi2O7, for K and η increasing with the increasing of Tb3+concentration.
关键词:Na3GdSi2O7;Tb3+;phosphor;rare earth;energy transfer
摘要:(Ba,Sr)3MgSi2O8:Eu2+,Mn2+ phosphor was synthesized by using 2.45 GHz high temperature microwave (MW) at a given firing temperature. The microwave non-thermal effect on the photoluminescence intensity of 660 nm emission was investigated. With an increase of MW power supply to reach an identical holding firing temperature, non-thermal MW effect leads to increasing transition probability of Eu2+ blue emission and indirect transition probability of Mn2+ red band emission with aid of energy transfer from Eu2+via (Ba,Sr)3MgSi2O8 host lattice. A modified energy level diagram was proposed to address this disturbing issue of MW energy attribute. This non-thermal MW effect suggests that a strong magnetic field may apply a disturbance effect on the structure and transition properties of the paramagnetic ions like Mn activator in microwave firing procedure.
关键词:(Ba;Sr)3MgSi2O8:Eu;Mn;660 nm;energy transfer;microwave power
摘要:A series of NaGdF4:Re(Re=Tm3+, Er3+, Yb3+) upconversion luminescence phosphors with various doping concentrations were prepared by a hydrothermal method. X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and upconversion (UC) emission spectra were used to characterize the samples. The results of XRD indicate that all the samples are hexagonal phase NaGdF4. The average crystallite sizes are estimated to be 41~43 nm. Under 980 nm laser excitation, the Er3+ and Yb3+ codoped NaGdF4 phosphors show green emission from 2H11/ 2→ 4I15/2 and 4S3/2→4I15/2 transitions of Er3+ ions, the red emissions attributed to 4F9/2→4I15/2 transitions of Er3+ ions, respectively. The Tm3+ and Yb3+ codoped NaGdF4 phosphors show blue emission from 1G4→3H6 transitions of Tm3+ ions, red emission assigned to 1G4→3F4 and 3F2,3→3H6 transitions of Tm3+ ions, near-infrared corresponding to the 3H4→3H6 transitions of Tm3+ ions, respectively. The upconversion luminescence intensity and a relative intensity of red, green and blue emission are governed by the doping Yb3+ concentrations in Er3+, Tm3+ and Yb3+ tridoped NaGdF4 phosphors. The possible upconversion luminescence mechanisms of the samples are discussed. The calculated CIE color coordinates display that the upconversion luminescence color can be tuned by varying the doping ions concentration.
摘要:Long-lasting phosphors Sr2MgSi2O7:Eu2+,Dy3+ were synthesized via hydrothermal-precipitation route. X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), as well as thermoluimnescence (TL) were utilized to characterize the long-lasting phosphors. XRD analysis indicates the obtained Sr2MgSi2O7:Eu2+,Dy3+ sample annealed at 1 000℃ for 4 h is tetragonal crystal phase. The crystallinity increases with temperature. The obtained phosphors consist of well dispersed submicron particles with a narrow size distribution of 200~300 nm, and these phosphor particles show blue emission corresponding to 5d-4f (467 nm) of Eu2+ under the excitation of visible light (399 nm). The afterglow time of sample synthesized at 1 100℃ is longer than those synthesized at 1 000℃ and 1 050℃. The thermoluminescence spectra of samples show broad bands centering at 330~340 K, which is suitable for the generation of long-lasting phosphorescence.
摘要:Two kinds of tetrapod-like zinc oxide nanostructures were fabricated using chemical vapor deposition method under argon and oxygen mixed ambient condition. The source materials were pure zinc powders. No catalyst was used during reaction. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy techniques were used to characterize their structures and optical properties. The nano productions are high purity zinc oxide with the wurtzite structure. Two kinds of zinc oxide nano productions possess three-dimensional structures, which are tetrapod-flake structure and tetrapod-wire structure, respectively. The nano productions have large length-diameter ratio and show a typical nano/micro-structure. By comparing the ultra-violet emission peak and visible emission band of the two zinc oxide nanostructures, the origin of the visible emission and the influence of their structures on optical emission properties are discussed.
摘要:Ca0.75MoO4:Eu0.253+,Ca0.75MoO4:Eu0.25-x3+,Bix3+ and Ca0.5MoO4:Eu0.25-2x3+,Bix3+,Li0.25+x+ were synthesized by co-precipitation method. The crystal structure, morphology and luminescent properties were measured and studied in detail by X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectrum, and photoluminescence spectrophotometer (PL). The synthesized red phosphors of CaMoO4:Eu3+,Bi3+,Li+ are scheelite structure, and the particle sizes are about 0.5~1 μm. The relative luminous intensity of Ca0.75MoO4:Eu0.25-x3+,Bix3+ is significantly higher than Ca0.75MoO4:Eu0.253+ because Bi3+ ions transmit the absorbed energy to Eu3+ ions. When the doping mole fraction of Bi3+ is 0.005, the relative luminous intensity of 616 nm main emission peak is the largest under the excitation of 395 nm. However, the phenomenon of concentration quenching occurs when Bi3+ doping concentration is higher. In addition, the incorporation of charge compensation can solve the problem of charge imbalance caused by the isomorphous substitution. It is shown that the luminescence property of Ca0.5MoO4:Eu3+0.23,Bi0.013+,Li+0.26 is significantly higher than Ca0.75MoO4:Eu0.253+, Ca0.5MoO4:Eu0.253+,Li0.25+, and Ca0.75MoO4:Eu0.243+,Bi0.013+ red phosphors.
摘要:UV mechanoluminescent (ML) phosphors SrMgSi2O6:Ce0.005, SrMgSi2O6:Ce0.005,Er0.015 and Sr2MgSi2O7:Ce0.005,Er0.015 were prepared via solid state reaction. The XRD results indicate that the structure of SrMgSi2O6 is identical to that of Sr2MgSi2O7, which has a tetragonal symmetry with a space group P421m.The emission bands of three samples are similar, which consist of a broad band with two peaks centered at 349 and 371 nm, caused by the f-d electron transition of Ce3+ ions. The ML results show that the ML intensities of these samples are well depended on the stress, indicating that these ML materials can be potentially used as sensors to detect the stress distribution of an object. Furthermore, the ML intensity of SrMgSi2O6:Ce0.005,Er0.015 is obviously higher than those of SrMgSi2O6:Ce0.005 and Sr2MgSi2O7:Ce0.005,Er0.015. The obtained results suggest that the trap and the worse symmetry of crystal structure are responsible for the higher ML intensity of SrMgSi2O6:Ce0.005,Er0.015. Because of the UV emission of this material, it can be used as the excitation source to irradiate other color phosphors and then the various colors ML can be realized.
关键词:mechanoluminescence;silicate phosphors;traps;symmetry of structure
摘要:The GaSb/GaAs quantum dots (QDs) were prepared by the technique of low pressure metalorganic chemical vapor deposition (LP-MOCVD). Based on analysis of samples for different growth temperatures, it turns out that the growth temperatures have little contribution to the morphology of GaSb/GaAs QDs and the shape of GaSb/GaAs QDs turns to be lens. The stress distributions between GaSb/GaAs interface lead to the "self-limiting" formation of GaSb QDs. Besides, due to discontinuous chemical potential of QDs, coupled with the effect of curing mechanism of Ostwald, the size distribution of QDs in certain range is discrete and two modes of QDs size appear. The surface mobility of antimony (Sb) adatoms has an important influence on the growth of GaSb/GaAs QDs. The discreteness of QDs can be efficiently improved by raising the growth temperature. With the process of heating up, the curing process of QDs can be presented.
摘要:High quality GaN epilayers have been grown on 6H-SiC substrate by metal organic chemical vapor deposition (MOCVD) using an in situ porous SiNx interlayer. It was found that the SiNx interlayer played a very important role in strain relief and the enhancement of quality of GaN epilayer. Optical microscope studies revealed that the crack line density was reduced to 0.29 mm-1. Furthermore, the in-plane stress of 1.58×10-3 was measured by Raman spectra, representing a significant strain relief. The relaxation was assisted by the reduction of dislocation density. Finally, a linear coefficient characterizing the relationship between the band gap and the biaxial stress of the GaN epilayer was obtained.
摘要:GZO transparent conductive films were prepared by RF magnetron sputtering. The influence of thickness on GZO films was studied by several methods, including atomic force microscopy, XRD, Hall Effect tester and UV-Vis spectrophotometer. LEDs with GZO transparent conductive layers were also fabricated. These results show that, as the thickness increases, the crystal quality is improved and the resistivity of the film is reduced. When the thickness reached 500 nm, the lowest resistivity of 2.79×10-4 Ω·cm and the highest transmittance of 97.9% at 460 nm wavelength were obtained. However, the variation of film thickness has little effect on the forward voltage of LED. But it is an important factor on improving the light extraction efficiency of LEDs.
摘要:In order to detect the hidden defects of the solar cells, the eletroluminescence image was obtained by applying a certain forward bias voltage to solar cell in the darkroom using the light sensor CCD camera. The experiments were carried out at three states: without optical filter, filtering the wavelength less than 800 nm, and filtering the wavelength greater than 800 nm. It is found that the detection effect is the best only under the lens of filtration of less than 800 nm wavelength. It proves that the cell mainly emits infrared light of 850~1 200 nm. By controlling the detecting time, it is found that the light intensity is varied with the detection time, and also varied with the forward bias voltage in the same detection time. This method can detect all kinds of hidden defect type of the solar cells. Under the reverse voltage,thin film cell appears small spots which show defect area and density, and the studies prove that thin film cell also can send infrared light and the defects exist in the cell. In detecting low power cell, it is found that there are serious defects in the cell. The results show that infrared detection has rapid and convenient intuitive features for solar cells defect detection.
摘要:High-quality ZnO and BeZnO films were grown on c-plane sapphire substrate using plasma-assisted molecular beam epitaxy (P-MBE) by inserting metal oxide buffer layers. X-ray diffraction(XRD) results show that all films have hexagonal wurtzite structure and highly c-axis orientation. The full width at half maximum (FWHM) of ZnO film is as low as 108 arcsec,and the FWHM of BeZnO film is less than 600 arcsec. The resonance Raman spectra show that both A1(LO) and A1(2LO) phonon modes shift to larger wavenumber with more Be doping. For the first time, the local vibration mode related to Be doping is found. The photoluminescence (PL) spectrum of ZnO films has only one emission peak(378 nm) at room temperature. However, another peak due to the strong free exciton emission is observed at low temperature (80 K). With the temperature increasing, the free exciton emission dominated over the bound exciton emission, and its peak shows gradual red shift. As for BeZnO film, the strong free exciton emission peak is not found at low temperature (80 K) due to the declined crystal quality caused by the incorporation of Be. It is also found that the peak position of BeZnO films in the PL and Raman spectra have local maximum values between 100~200 K, which is suggested to be caused by the stress effect due to the thermal expansion mismatch of the alloy lattices.
摘要:A kind of metal gratings based on surface plasmon coupling was presented in this paper. The metal grating has different transmission rate according to incident direction because of different surface plasmon coupling conditions. The unsymmetrical transmission phenomenon appears for the Au-SiO2 grating when the periodic is 500 nm and the filling factor is 0.7, particularly for wavelength from 565 to 589 nm. A maximum transmission contrast of more than 3×104 is found at filling factor 0.662. When the thickness of Au is 60 nm, the transmission contrast is more than 5 during 570~630 nm, and the maximum transmission is 43%. When the periodic is 1 100 nm, the transmission contrast is more than 5 during 1 530~1 590 nm, which satisfies for the mid-infrared applications.
摘要:ZnO-based thin film transistors (ZnO-TFTs) with RF-sputtered ZnO active layer were fabricated at room temperature, and then annealed at 350℃ for 1 h in the air environment. Effects of channel width on the electrical properties of ZnO-TFTs were investigated. The threshold voltage increases with the decrease of the channel width, that is because the more narrower the channel width is, the more greater probability of carriers is captured, the less free carriers are under the same gate voltage, so that the more greater the threshold voltage is. The saturation carrier mobility also increases with the decrease of the channel width, due to the side wall effect associated with source/drain resistance as well as the fringing electronic-field effects which led to an additional current flow beyond the device edges.
摘要:The current crowding effect of low-power GaN base LEDs was investigated. It is found that LED module (eight LEDs in series as a set of group) suffered voltage surge sometimes presented current leakage failure. Pspice was applied to simulate LED module. It showed the damaged samples bore more voltage and power compared with the normal results. The orientation of leakage current of LED chip was studied via Emission Microscope (EMMI), the result indicated the leakage current intensively spreaded on the end of the p-type extended electrode. We assumed that the damaged route of voltage surged through the quantum well of LED, and the un-distribution current led to the effect of current crowding near the p-type extended electrode, which aggravated the injury severity of pn junction. Well-distributed current could improve the reliability of LED. Finally, the failure analysis of LED with differential negative resistance effect in the current-voltage characteristics was given.
摘要:Heavily p+-doped GaAsSb is extensively applied in InP HBT base material, it influences many important parameters, such as band gap and Fermi level. These parameters are key factors for the design of high performance HBT devices. This work studied photoluminescence of p+- GaAsSb in the model of indirect transition, especially the relationship between GaAsSb Fermi level and Sb composition. The hole effective mass (mh) and hole density (nh) were measured and calculated because Fermi level, mh and nh had functional relationship. It is found that mh and nh result in the change of Fermi level.
摘要:Human have different sensitivity under different wavelengths of light. By using dose work method, physiological parameter method and fatigue evaluation method, the human optical biorhythm effect of 30 students with normal vision was studied under the blue LED, whose peak wavelengths are 468, 457, and 453 nm. In the dose work method, the influence of blue LED on the error rate, speed of work, and the brainwork efficiency is: 453 nm<457 nm<468 nm. In physiological parameter method, 468 nm blue LED has the greatest impact on the changes of pulse, and insignificant on systolic/diastolic blood pressure. In fatigue evaluation method, effect of blue LED on human comfort is: 453 nm<457 nm<468 nm. In conclusion, 468 nm blue LED has great influence on human optical biological rhythm.
摘要:Three dimensional fluorescence spectra of fresh orange juice and orange juice beverages (8 brands) were obtained by employing FLS920 spectrometer. The fluorescence mechanism and characters of fresh orange juice and different kinds of pure food additives in beverage foods were analyzed. The optimal excitation wavelength and fluorescence peak wavelength of orange juice are 470 nm and 526 nm, respectively. The characteristic peak of orange juice is 470/526 nm, and other peaks belong to food additives. Meanwhile, By extracting the center of gravity of three dimensional fluorescence spectroscopy, and combining the robust Mahalanobis distance based on MCD estimator, the orange juice beverages were classified, and the classification results were ideal. The results indicate that the combination of spectral detection and pattern recognition can contribute to the classification of beverages.
关键词:orange juice beverages;spectral analysis;robust Mahalanobis distance;pattern recognition
摘要:A kind of metal-dielectric-metal (MDM) plasmonic waveguide with double parallel cylindrical nanorods was investigated. The propagation properties of the waveguide structure were analyzed using the finite-difference time-domain (FDTD) method. The results show that the electromagnetic field is well confined to the dielectric layer and the intermediate region formed by the two cylindrical nanorods when the incident light is perpendicular to the major axis, so the filed can be efficiently coupled into the waveguide. At the working wavelength λ=1 550 nm, the effective index decreases with the increase of the inner radius r1, meanwhile the propagation length increases as the inner radius r1 increases. However, in the case of larger d, the effective index becomes large, and the propagation length becomes short. In addition, the field can be predominantly confined within the dielectric layer in the case of g=20 nm. In short, adjusting the geometrical parameters can significantly improve the confinement of the SPPs fields and reduce the losses of the waveguide, so that the effective refractive index and propagation length of the waveguide can be optimized. Subwavelength optical confinement can be achieved in this kind of plasmonic waveguide, which will be applied to the fields of photonic device integration and sensors.
摘要:The mirror periodic photonic crystal heterostructures (ABCCBA)N were studied in this paper. First, the optical propagation method of one-dimensional dielectric system,the transfer matrix method, was used to deduce the transmittance of photonic crystal heterostructures. And then, the Matlab software and the formula were adopted to simulate and describe the relationship between photonic bandgap form and mirror periodic numbers, photonic bandgap numbers and the layer thickness of photonic crystal, the incoming angle and the position of photonic bandgap. The results show that the formation and change of photonic band gap are mainly affected by the change of the layer thickness of photonic crystal and the incoming angle. By altering the photonic bandgap parameters, the photonic bandgap with different frequency can be gotten, and can be used to make high quality mirrors, filters, and light-emitting diodes.
摘要:Sarcandra glabra is one of the traditional Chinese medicine. A method was demonstrated to measure it by surface enhanced Raman spectrum (SERS) technology. Silver colloid was prepared by using aqueous reduction of silver nitrate with trisodium citrate. SERS in the samples of Sarcandra glabra was detected by taking silver nanoparticles as enhancing substrates. After disposed by the silver colloid, the intensity of the SERS signal of Sarcandra glabra stem section increased obviously. In SERS of Sarcandra glabra samples, the characteristic peaks were observed at 637, 1 176, 1 309, 1 476, 1 612 cm-1. The SERS signal of Sarcandra glabra was assigned tentatively to some biochemical substances and molecular structure including benzopyrone ring, methoxy and phenolic hydroxyl group through a derivative spectrum of Sarcandra glabra and Isofraxiden. The results show that the SERS might provide a new, precise and convenient method for the research of tradition Chinese medicinal materials.
摘要:A highly sensitive magnetic particle-based chemiluminescence immunoassay (CLIA) technique for assaying thyroid stimulating hormone (TSH) in serum was described. Fluorescein isothiocyanate (FITC) and N-(aminobutyl)-N-(ethylisoluminol) (ABEI) were used to label two different monoclonal antibodies of anti-TSH. Both of the labeled antibodies combined with TSH to form a sandwiched immunoreaction that was monitored by chemiluminescence (CL) detection. The magnetic particles (MPs) that were coated with anti-FITC antibody served as both the solid phase and the separator. The method showed high sensitivty with a detection limit of 0.01 μIU/mL. The coefficient of variation of intra-assay imprecision and the inter-assay imprecision were less than 10%. The average recoveries were 96%~103%. A correlation analysis against an established automated assay generated a correlation coefficient of 0.993 7. The proposed method demonstrates an acceptable performance for quantifying serum TSH and is suitable for the clinical lab.
摘要:Laser interference could weaken or deprive the detection abilities from CCD imaging detection system. Therefore, how to evaluate the performance of laser jamming objectively, precisely and quantitatively becomes a significant link in the study of interference techniques. This paper surveys the principles of Compressed Sensing(CS) theory and a new image metric which is based on the CS theory has been proposed. Combining with the characteristics of laser jamming image and its influence on CCD detection algorithms, the new metric takes advantage of the available clutter metric. Moreover, it has been applied in the performance evaluation of detection algorithms when jammed by laser. Experimental results of laser jamming in the field of view show that the metric can reflect the influence of laser jamming on CCD imaging detecting algorithms and realize the quantitative appraisal of laser jamming performance on CCD imaging system, therefore, its validity is verified.