石墨烯光致掺杂研究进展

石墨烯因其自身碳原子2D的sp^(2)杂化结构特点以及优异的力学、光学和电学性能在能源、传感、生物医学和柔性可穿戴设备等领域具有广阔的发展前景。为了实现基于石墨烯的各种电子和光电子器件的实际应用,有效调控其掺杂及能带结构是亟须解决的重要问题之一。相比于传统的晶格原子置换与表面化学修饰等方法,近十几年发展起来的一种基于外场的表面物理调控方法——光致掺杂调控法,由于具有调控灵活性好、掺杂浓度可控性强、操作容易且对石墨烯载流子迁移率影响小的优点已成为一个新的研究热点。在目前的研究中,石墨烯的光致掺杂主要通过表面气体分子吸附、衬底电荷作用以及光活性物质诱导三种方式实现并被应用于原位p-n结制备以及光电子器件(如太阳能电池和光电探测器)性能优化等方面。本文综述了石墨烯光致掺杂的机制和研究现状,最后展望了其未来的发展前景。相比于其他光致掺杂方法,基于光活性物质诱导的石墨烯光致掺杂因具有掺杂速度快、浓度高、稳定性好以及可控性强的特点具有广阔的应用前景。

Energy Transfer Probability Between Host and Guest in Doped Organic Electrophosphorescent Devices

An expression for energy transfer probability （η） between host （TPD） and guest （Ir（ppy）3） phosphorescent systems is proposed,and the energy transfer process in doped organic electrophosphorescent （EP） devices is discussed. The results show that （1） The rate of the triplet energy transfer （KHG and KGH） exponentially increases with the host-guest molecular distance （R）, and KHG decreases quickly as the intermolecular distance of the guest （RGG） increases. In addition,the KHG/KGH ratio of the dopant system increases when R or RGG is reduced; （2） The energy transfer probability approximately linearly decreases as R increases from 0.8 to 1.2nm,and the variation of RGG can be neglected when R〈1.1nm. For 1. 1nm〈R〈l. 2nm, RGG （〈1.6nm） plays an increasingly important role when 71 drops with the latter＇ （3） η increases when the Forster energy transfer rate increases or Gibb＇s energy declines.

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloys

The transitions of E0 ,E0 ＋A0, and E＋ in dilute GaAs（1-x） Nx alloys with x = 0.10% ,0.22% ,0.36% ,and 0.62% are observed by micro-photoluminescence. Resonant Raman scattering results further confirm that they are from the intrinsic emissions in the studied dilute GaAsN alloys rather than some localized exciton emissions in the GaAsN alloys. The results show that the nitrogen-induced E E＋ and E0 ＋ A0 transitions in GaAsN alloys intersect at a nitrogen content of about 0.16%. It is demonstrated that a small amount of isoelectronic doping combined with micro-photoluminescence allows direct observation of above band gap transitions that are not usually accessible in photoluminescence.

Synthesis and Characterization of TiO2 Doped ZnO Microtubes

The TiO2-doped ZnO microtubes have been successfully fabricated via a wet chemical method, using zinc chloride and titanium sulphate as the starting materials. The assynthesized products were characterized by X-ray diffraction, field emission scanning electron microscopy and room temperature photoluminescence measurement. The photocatalytic activity in degrading methyl orange was measured with a UV-Vis spectrophotometer. The pure ZnO microtubes exhibit an exact hexangular hollow structure with a diameter of about 700 nm, a length of 3 μm and a wall thickness of about 40 nm. The TiO2-doped ZnO microtubes with TiO2/ZnO ratio less than 5% have the same dimension with the pure ZnO microtubes, a smooth column shape, not a hexangular structure. The growth of ZnO may be inhibited by the more Ti^4＋ doped into ZnO structure to achieve a small dimension or a multiphase. The crystallinity of ZnO microtubes decreases with increasing TiO2 content, and then a multiphase containing ZnO, Ti305 and TiO occur when the TiO2/ZnO ratio is more than 5%. The UV emission intensity of the TiO2-doped ZnO obviously increases and then tends to decrease with TiO2/ZnO ratio increasing. The photocatalytic properties of the TiO2-doped ZnO microtubes are very efficient in degrading organic dyes of methyl orange and are well identical with its PL properties and the crystallinity.

Optical properties and photocatalytic activity of Nd-doped ZnO powders

To improve the photocatalytic activity of zinc oxides, ZnO powders doped with different neodymium （Nd） concentrations were prepared via hydrothermal method. X-ray diffraction （XRD） together with X-ray photoelectron spectroscopy （XPS） patterns revealed that Nd atoms were successfully incorporated into the ZnO lattice. XRD pattern also showed some anisotropy of the powders. The photoluminescence （PL） spectrum demonstrated a strong and broad peak in the visible light region, and the intensity of visible light emission was enhanced by Nd-doping. The photocatalytic activity was evaluated by the degradation of methyl orange solution. It is shown that doping of Nd into ZnO induces an increase of the photocatalytic activity and it attains to optimum at 3% （mole fraction） doping concentration. The intense visible light emission and the enhanced photocatalytic activity were explained by the increase in electron hole pairs and induced defects like antisite oxygen Ozn and interstitial oxygen Oi, due to the doping of Nd.

White organic light-emitting diodes based on emission from DPVBi-doped 4,48-bis (2,28-diphenylvinyl)-1,18-biphenyl

White organic light-emitting diodes were fabricated by using 4,48-bis （2,28-diphenylvinyl） -1,18-bi- phenyl （DPVBi） as a dopant with a structure of ITO/4,4＂-bisEN-（1-naphthyl-1-）-N-phenyl-amino]-bi- phenyl （NPB,50 nm）/NPB：DPVBi （molecular weight ratio 10 ; 1,30 nm）/tris-（8-hydroxyquinoline）a- luminum（AIq：, ,20 nm）/LiF（1 nm）/Al. A broad emissive band with four major peaks of 438,464,496 and 520 nm was obtained by electroluminescence spectra,of which 438 nm-,464 nm- and 520 nm-peak come from emission of NPB, DPVBi and AIq3, respectively,and 496 nm-one resulted from the emissive superposition of three materials above. The emission from DPVBi was attributed to the charge trapping from NPB. The emission region was transferred partly from AIq3 to DPVBi-doped NPB by introducing the dopant DPVBi,which leads to emission of DPVBi and an enhanced emission from NPB. The maxi- mum luminance and current efficiency were 4721 cd/m^2 at 22 V and 0.80 cd/A at 5V,respectively.

Photoluminescence of the Beryllium Acceptor at the Centre of Quantum Wells

We report photoluminescence studies of internal transitions of shallow Be acceptors in bulk GaAs and a series of S-doped GaAs/ALAs multiple quantum well samples with well width ranging from 3 to 20nm. A series of Be S-doped GaAs/ AlAs multiple-quantum wells with the doping at the well center and a single epilayer of GaAs uniformly Be doped were grown by molecular beam epitaxy. The photoluminescence spectra were measured at 4,20,40, 80, and 120K, respectively. A two-hole transition of the acceptor-bound exciton from the ground state, 1S3/2 （/8）, to the first-excited state, 2S3/2 （Г6） , has been clearly observed. A variational principle is presented to obtain the 2s-1s transition energies of quantum confined Be acceptors as a function of the well width under the single-band effective mass and envelop function approximations. It is found that the acceptor transition energy increases with decreasing quantum-well width, and the experimental results agree well with the theoretical calculation.

Monodisperse Upconversion NaYF4 Nanocrystals： Syntheses and Bioapplications

A facile strategy using cheap and readily available precursors has been successfully developed for the synthesis of rare-earth doped hexagonal phase NaYF4 nanocrystals with uniform shape and small particle size as well as strong photoluminescence. Due to their optical properties and good biocornpatibility, these multicolor nanocrystals were successfully used as a bio-tag for cancer cell imaging. This novel synthetic method should also be capable of extension to the synthesis of other fluoride nanocrystals such as YF3 and LaF3.

Photoluminescence investigation on highly p^+ -doped GaAs_(1-y)Sb_y(y<0.3)

Photoluminescence properties of highly p＋-doped GaASl_ySby are investigated. Band gap narrowing （BGN） effect is considered for heavily doped GaAs1_ySby epilayers. Band-gap Eg（GaAsl_ySby）=l.25y2-1.95y＋1.519 is obtained through fitting band-gap energy obtained by PL spectra from 35 to 300 K. Fermi level （El） and full width at half maximum （FWHM） of photolumines- cence increase with antimony mole fraction. The increase of Fermi level is attributed to hole mass of GaAsl_ySby decrease which is resulted from antimony composition increase. The increase of Fermi level means that more electrons participate in in- direct transition to result in FWHM increases.

Enhanced photoluminescence from porous silicon microcavities by rare earth doping

The photoluminescence(PL) properties of porous silicon microcavities(PSMs) in the visible range at room temperature are improved by doping the rare earth ytterbium(Yb) into PSMs prepared by the electrochemical etching method.It is observed that PSMs doped with the rare earth have an emission band around 630 nm.Compared with the single-layer porous silicon(PS) film,the PSMs doped with Yb have narrower and stronger PL spectrum.

Phase transition and photoluminescence properties of Eu^3＋-doped ZnMoO4 red phosphors

Eu3＋-doped ZnMoO4 with different doping concentrations were synthesized by a hydrothermal method. The effects of Eu3＋ doping on the phase structure and photoluminescence （PL） properties of ZnMoO4 were investigated. The result showed that the introduction of Eu3~ could lead to phase transition of ZnMoO4. With the increase of Eu3-- doping amount, [3-ZnMoO4 was transformed to ct phase gradually, which led to different photoluminescence performances. The optimized doping concentration of Eu3＋ was 6 mol% for the highest emission intensity at 615 nm. Its CIE chromaticity coordinates were （0.667, 0.331）, which were very close to the values of standard chromaticity （0.67, 0.33） for National Television Standards Committee （NTSC） system. Therefore, Eu3＋-doped ZnMoO4 is considered to be a promising red-emitting phosphor for white LED applications.

Structure characterization,magnetic and photoluminescence properties of Mn doped ZnS nanocrystalline

Wurzite ZnS:Mn nanorods are synthesized via a solvothermal method by using ethylenediamine and water as mixed solvent.The diameters of the nanorods increase and the lengths decrease with the Mn concentration.High resolution transmission electron microscopic images illustrate that a few cubic ZnS:Mn nanoparticles arise along with hexagonal nanorods on high Mn concentration.The samples set off yellow-orange emission at 590 nm,characteristic of 4 T→ 6 A 1 transition of Mn 2+ at T d symmetry in ZnS.Electron spin resonance spectrum of the nanorods shows that high Mn concentrations produce a broad envelope,whereas six-line hyperfine appears for lower Mn concentrations.These results together with the magnetization curves indicate that all the ZnS:Mn samples are paramagnetic even down to 4 K,which suggests that the ZnS:Mn is not suitable for dilute magnetic semiconductor.

Composition-induced valence variation of europium and the photoluminescence properties for Eu^(2+) doped borophosphate luminous glass in air

A simultaneous blue-light and red-light emitting glass of SrO-B2O3-P2O5 doped with Eu2O3 is prepared in air, and then heat-treated without any reductive reagent. A transition combination is found to consist of a band emission peaked around 430 nm and a series of line emission from 593 nm to 611 nm, corresponding to the typical 4f65d→ 4f7 transition of Eu2+ and 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+, respectively. Some unidentified crystals such as Sr (PO3)2 and SrB2O4 as hosts for Eu2+ with more stronger crystal field lead to this enhancement of photoluminescence (PL) intensity superior to the asprepared parent glass.

Organic light emitting devices employing non-doped structure

A kind of efficient non-doped white organic light-emitting diodes(WOLEDs) were realized by using a bright blue-emitting layer of 4,4-bis(2,2-diphenylvinyl)-1,1-biphenyl(DPVBi) combining with red emitting ultrathin layer of [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene]propane-dinitrile(DCM2) and green emitting ultrathin layer of 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H, 11H(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one(C545T) with different thicknesses of 0.05 nm, 0.10 nm and 0.20 nm. For comparing, a doped WOLED was also fabricated, in which C545 T and DCM2 are codoped into DPVBi layer to provide blue, green and red emission for obtaining white emission. The maximum luminance and power efficiency of the doped WOLED are 5 765 cd/m^2 at 16 V and 5.23 lm/W at 5 V, respectively, and its Commission Internationale de l'Eclairage(CIE) coordinate changes from(0.393 7, 0.445 3) at 5 V to(0.300 7, 0.373 8) at 12 V. When the thickness of the ultrathin C545 T layer in non-doped WLEDs increases, the emission luminance increases, but all non-doped devices are in the yellow white region. The device with 0.10-nm-thick C545 T has a maximum efficiency of 15.23 cd/A at 8 V and a maximum power efficiency of 6.51 lm/W at 7 V, and its maximum luminance is 10 620 cd/m^2 at 16 V. CIE coordinates of non-doped WLEDs with C545 T thickness of 0.05 nm, 0.10 nm and 0.20 nm are(0.447 3, 0.455 6),(0.464 0, 0.473 1) and(0.458 4, 0.470 0) at 8 V, respectively.