Enhanced photoluminescence of monolayer MoS_(2)on stepped gold structure

Different Mo S_(2)/Au heterostructures can play an important role in tuning the photoluminescence(PL)and optoelectrical properties of monolayer Mo S_(2).Previous studies of PL of Mo S_(2)/Au heterostructures were mainly limited to the PL enhancement by using different Au nanostructures and PL quenching of monolayer Mo S_(2)on flat Au surfaces.Here,we demonstrate the enhanced excitonic PL emissions of monolayer Mo S_(2)/Au heterostructures on Si/Si O_(2)substrates.By transferring the continuous monolayer Mo S_(2)onto a stepped Au structure consisting of 60-nm and 100-nm Au films,the Mo S_(2)/Au-60 and Mo S_(2)/Au-100 heterostructures exhibit enhanced PL emissions,each with a blue-shifted PL peak in comparison with the Mo S_(2)/Si O_(2).Furthermore,the PL intensity of Mo S_(2)/Au-60 is about twice larger than that of Mo S_(2)/Au-100.The different enhanced excitonic PL emissions in Mo S_(2)/Au heterostructures can be attributed to the different charge transfer effects modified by the stepped Au structure.This work may provide an insight into the excitonic PL and charge transfer effect of Mo S_(2)on Au film and yield novel phenomena in Mo S_(2)/Au heterostructures for further study of PL tuning and optoelectrical properties.

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots（QDs） are fabricated on Si nanowires（NWs） substrates with and without Au nanoparticles（NPs）. The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence（PL） intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.

Surface plasmon enhanced photoluminescence in amorphous silicon carbide films by adjusting Ag island film sizes

Ag island films with different sizes are deposited on hydrogenated amorphous silicon carbide （a-SiC：H） films, and the influences of Ag island films on the optical properties of the tx-SiC：H films are investigated. Atomic force microscope images show that Ag nanoislands are formed after Ag coating, and the size of the Ag islands increases with increasing Ag deposition time. The extinction spectra indicate that two resonance absorption peaks which correspond to out-of-plane and in-plane surface plasmon modes of the Ag island films are obtained, and the resonance peak shifts toward longer wavelength with increasing Ag island size. The photoluminescence （PL） enhancement or quenching depends on the size of Ag islands, and PL enhancement by 1.6 times on the main PL band is obtained when the sputtering time is 10 min. Analyses show that the influence of surface plasmons on the PL of a-SiC：H is determined by the competition between the scattering and absorption of Ag islands, and PL enhancement is obtained when scattering is the main interaction between the Ag islands and incident light.

Chemically engineered dendrite growth of uniform monolayers MoS_(2) for enhanced photoluminescence[Invited]

Large area and uniform monolayer MoS_(2)is of great importance for optoelectronic devices but is commonly suffering from rather weak photoluminescence.Here,by engineering the concentration profiles of gaseous chemicals through extra trace amounts of water,we demonstrate the uniform dendrite-type growth of monolayer MoS_(2)unraveled by spatially resolved fluorescence spectroscopy,which exhibits macroscopic monolayer flakes [up to centimeter scale] with photoluminescence intensity of orders of magnitude higher than conventional chemical vapor deposition monolayer MoS_(2).Both spectroscopic evidence and theoretical models reveal that the fast-fractal dendrite growth can be ascribed to the extra introduced water sources that generate sufficient aqueous gas around the S-poor regions nearby the central-axis zone,leading to highly efficient Mo sources transport,accelerated S atom corrosion nearby grain edges,and/or defect sites,as well as enhanced photoemission intensity.Our results may provide new insight for high throughput fabrication of MoS_(2)monolayers with high yield photoluminescence efficiency.

Effectively enhanced photoluminescence of CePO_(4):Tb^(3+)nanorods combined with carbon dots

CePO_(4):Tb^(3+)nanorods were successfully obtained via a simple hydrothermal method and combined with carbon dots(CDs)to obtain CDs@CePO_(4):Tb^(3+)nanorods.Due to the combination of CDs,the emission intensity of CDs@CePO_(4):Tb^(3+)nanorods increases about 92 times,compared with that of CePO_(4):Tb^(3+)nanorods.The combination of CDs and CePO_(4):Tb^(3+)nanorods was confirmed by Fourier transform infrared spectroscopy(FTIR),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS)and so on.The mechanism of luminescence enhancement may be attributed to some aspects:the formation of hexagonal phase results in the increase of crystal field symmetry,and the energy transfer among CDs,Ce^(3+)and Tb^(3+)ions,which causes the Tb^(3+)ions in CDs@CePO_(4):Tb^(3+)nano rods to obtain mo re excited energy and less non-radiative atte nuation co mpared to CePO_(4):Tb^(3+)nano rods.The luminescence enhancement strategy through combination of CDs would provide a simple and effective approach for other rare earth ions doped luminescent materials.

Photoluminescence Enhancement of Aluminum Ion Intercalated MoS_(2)Quantum Dots

Low photolumines-cence(PL)quantum yield of molybdenum disulfide(MoS_(2))quan-tum dots(QDs)has lim-ited practical applica-tion as potential fluores-cent materials.Here,we report the intercalation of aluminum ion(Al^(3+))to enhance the PL of MoS_(2)QDs and the un-derlying mechanism.With detailed characterization and exciton dynamics study,we suggest that additional surface states including new emission centers have been effectively introduced to MoS_(2)QDs by the Al^(3+)intercalation.The synergy of new radiative pathway for exciton re-combination and the passivation of non-radiative surface traps is responsible for the en-hanced fluorescence of MoS_(2)QDs.Our findings demonstrate an efficient strategy to improve the optical properties of MoS_(2)QDs and are important for understanding the regulation effect of surface states on the emission of two dimensional sulfide QDs.

Anomalous photoluminescence enhancement and resonance charge transfer in type-II 2D lateral heterostructures

Type-Ⅱband alignment can realize the efficient charge transfer and separation at the semiconductor heterointerface,which results in photoluminescence(PL)quenching.Recently,several researches demonstrated great enhancement of localized PL at the interface of type-Ⅱtwo-dimensional(2D)heterostructure.However,the dominant physical mechanism of this enhanced PL emission has not been well understood.In this work,we symmetrically study the exciton dynamics of type-Ⅱlateral heterostructures of monolayer MoS_(2) and WS_(2) at room temperatures.The strong PL enhancement along the one-dimensional(1D)heterointerface is associated with the trion emission of the WS_(2) shell,while a dramatic PL quenching of neutral exciton is observed on the MoS_(2) core.The enhanced quantum yield of WS2trion emission can be explained by charge-transfer-enhanced photoexcited carrier dynamics,which is facilitated by resonance hole transfer from MoS_(2) side to WS_(2) side.This work sheds light on the 1D exciton photophysics in lateral heterostructures,which has the potential to lead to new concepts and applications of optoelectronic device.

Transforming bilayer MoS2 into single-layer with strong photoluminescence using UV-ozone oxidation

The use of single-layer MoS2 in light emitting devices requires innovative methods to enhance its low photoluminescence （PL） quantum yield. In this work, we report that single-layer MoS2 with a strong PL can be prepared by oxidizing bilayer MoS2 using W-ozone oxidation. We show that as compared to mechanically-exfoliated single-layer MoS2, the PL intensity of the single-layer MoS2 prepared by W-ozone oxidation is enhanced by 20-30 times. We demonstrate that the PL intensity of both neutral excitons and trions （charged excitons） can be greatly enhanced in the oxidized MoS2 samples. These results provide novel insights into the PL enhancement of single-layer MoS2.

Photoluminescence manipulation in two-dimensional transition metal dichalcogenides

Two-dimensional transition metal dichalcogenides(TMDCs)have been regarded as an intriguing platform for exploring novel physical phenomena and optoelectronic devices due to their excitonic emission characteristics derived from the atomic thin thickness and reduced dielectric screening effect.Notably,monolayer TMDCs with a direct bandgap exhibiting strong photoluminescence(PL)are promising candidates for the light-emitting devices,while the interlayer excitons in heterostructures hold great potential for the photonic chips and optical communication applications.However,the non-ideal photoluminescent intensity and quality due to the ultrathin thickness and high defect density of experimentally obtained monolayer TMDCs limit the further development for the light-emission applications.Here,we summarize the research progress on the PL manipulation of the excitonic emission in TMDCs,where the PL intensity enhancement and emission wavelength regulation are included.The concept and characteristics of excitons are overviewed firstly,followed by the discussion on the evaluation and characterization of excitonic emission.The state-of-the-art progress on the manipulation of the neutral excitons and interlayer excitons PL are then summarized.Finally,the challenges and prospects are proposed.

Synthesis and Photoluminescence Enhancement of Silver Nanoparticles Decorated Porous Anodic Alumina

Silver nanoparticles（Ag NPs） were successfully assembled in porous anodic alumina（AAO） templates via a green silver mirror reaction.The Ag NPs/AAO composite templates then were characterized by field emission scanning electron microscopy（FESEM）,energy-dispersive X-ray microanalysis（EDX）,and X-ray diffraction（XRD）.Furthermore,the photoluminescence（PL） properties were also investigated.Compared with the blank AAO,the PL intensity of Ag NPs/AAO templates are enhanced and the maximum enhancement is 2.58 times.Based on the local electric field enhancement effect,the theoretical values were also deduced,which are basically coincident with the experimental.

Substitutional oxygen activated photoluminescence enhancement in monolayer transition metal dichalcogenides

Atomically thin transition metal dichalcogenides(TMDCs)are intriguing semiconductors for photonics and optoelectronics,and therefore enhancing their photoluminescence(PL)efficiency is crucial for these applications.Many efforts have been contributed to enhancing the PL performance of monolayer TMDCs,yet the complexity between the microstructure and the PL efficiency has hindered the manipulation of their PL properties.Here we demonstrate that the PL intensity of the monolayer TMDC can be enhanced by nearly one order of magnitude with a~20%narrower spectral linewidth after a pre-activation plateau using laser irradiation in ambient environment.Combined experimental and theoretical studies reveal that low-power laser irradiation generates many sulfur vacancy clusters,which are subsequently filled up by oxygen,and the lattice substitutional oxygen clusters induce the dramatic PL enhancement of monolayer WS;.Such PL enhancement phenomenon is found to be universal for other monolayer TMDCs,and thus would benefit their versatile optical applications.

Pressure Distinguishes the Dual Emissions in Pseudohalide 2D Ruddlesden-Popper Perovskite Cs_(2)Pb(SCN)_(2)Br_(2)

Two-dimensional(2D)Ruddlesden-Popper(RP)halide perovskites with diverse structures and properties have drawn increasing attention due to their promising optoelectronic applications.Recently,a new all-inorganic Cs_(2)Pb(SCN)_(2)Br_(2) has been reported that opens up new potential for the development of 2D RP perovskites.However,recent reports of unusual dual emissions and two-edge absorption in Cs_(2)Pb(SCN)_(2)Br_(2) have generated intense debate about its origin and remains controversial.Here,by combining continuous pressure tuning with in situ diagnostics,we have unambiguously revealed the underlying mechanisms that the 2D Cs_(2)Pb(SCN)_(2)Br_(2) exhibits an intrinsic blue emission at 2.66 eV and an absorption edge close to the emission peak.While the gradually formed CsPbBr_(3) is responsible for the green emission at 2.33 eV with the absorption shoulder at 2.41 eV.Furthermore,by fitting the temperature-dependent intensity of the intrinsic blue emission,we have determined the corrected value of exciton binding energy for 2D Cs_(2)Pb(SCN)_(2)Br_(2) to be 90 meV.Intriguingly,an emission enhancement of 2.5 times is achieved in Cs_(2)Pb(SCN)_(2)Br_(2) under a mild pressure within 0.8 GPa,caused by the pressuresuppressed exciton-phonon interaction.This work not only elucidates the origin of the dual emissions and two-edge absorption in Cs_(2)Pb(SCN)_(2)Br_(2),but it also provides a potential means to regulate and optimize the optoelectronic properties of 2D perovskites.

一种实现单层MoS_(2)光致发光显著增强的有效缺陷工程策略

二维过渡金属硫族化合物(TMDCs)材料被认为是拓展摩尔定律的极具前景的候选材料.然而,该材料的低光致发光效率严重限制了其实际应用,其本质源于材料制备中不可避免引入的缺陷.在本文中,我们报道了一种Sr掺杂单层MoS_(2)的有效缺陷工程策略,该策略在实验上通过简便的化学气相沉积(CVD)一步法成功实现.所制备的具有亚毫米(~324μm)级的大尺寸样品的光致发光可实现高达两个数量级的增强,并伴随着载流子寿命的显著增强.这一现象主要归因于Sr掺杂后MoS_(2)体系中其三激子向激子转换.与此同时,掺杂样品的辐射质量和稳定性也显著提升.第一性原理计算进一步阐明了其调控机制,即在MoS_(2)中引入适当互补缺陷能级与其自身的缺陷能级协同,从而可调节其载流子组分,以实现光致发光的显著增强.此外,我们的缺陷工程策略也适用于其他掺杂剂,如钙掺杂剂.我们的工作报告了一种可以显著提升单层MoS_(2)的荧光性能的有效缺陷工程策略,这为设计和调控二维TMDCs的光电特性提供一种极具前途的方法.

Highly efficient solid-state luminescence of carbonized polymer dots without matrix

Development of high-performance solid state luminescent carbon-based nanomaterials remains challenging.Here,strong blue-green fluorescent carbonized polymer dots(CPDs)from o-aminobenzenethiol and thiosalicylic acid(o ABT-TSA-CPDs)with an absolute photoluminescence quantum yield(PLQY)of 76%in solid state without matrix were synthesized.Through adjusting the reaction temperature and time,the PL centers were proved to be carbon core state and surface state associated to carbonyl group which was the source of strong fluorescence emission in solid state.The mechanism of the unique phenomenon of enhanced emission from ethanol solution(PLQY=7%)to powder(PLQY=76%)was investigated by analyzing the chemical properties and structures of o ABT-TSA-CPDs at different temperatures and o ABT-TSACPDs/PVC composites,and was confirmed as fixation of PL centers.

Tailoring optical and photocatalytic properties by single-Ag-atom exchange in Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8) nanoclusters

Precise mono-doping of metal atom into metal particles at a specific particle position(e.g.,the central site)in a highly controllable manner is still a challenge.In this work,we develop a highly controllable strategy for exchanging a single Ag atom into the central gold site of Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8)(Ph=phenyl)nanoclusters.Interestingly,a“pigeon-pair”cluster of{[Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8)]·[Au_(12)Ag_(13)(PPh_(3))_(10)C_(l8)]}^(2+)is obtained and confirmed by electrospray ionization mass spectrometry(ESI-MS),thermogravimetric analysis(TGA)and single crystal X-ray diffraction(SCXRD)analysis.The experimental results and density functional theory(DFT)calculations suggest that the single-metal-atom exchanging from[Au_(13)Ag_(12)(PPh_(3))_(10)C_(l8)]^(+)to[Au_(12)Ag_(13)(PPh_(3))_(10)C_(l8)]^(+)occurs at the central position through the side entry of theμ_(3)-bridging Cl atoms.Finally,the effects on the electronic structure and properties caused by the single-atom exchange at the central site are shown by the enhancement of fluorescence and catalytic activity in the photocatalytic oxidation of ethanol.