Exploring plasmons weakly coupling to perovskite excitons with tunable emission by energy transfer

Localized surface plasmon resonance(LSPR) has caused extensive concern and achieved widespread applications in optoelectronics. However, the weak coupling of plasmons and excitons in a nanometal/semiconductor system remains to be investigated via energy transfer. Herein, bandgap tunable perovskite films were synthesized to adjust the emission peaks,for further coupling with stable localized surface plasmons from gold nanoparticles. The degree of mismatch, using steadystate and transient photoluminescence(PL), was investigated systematically in two different cases of gold nanoparticles that were in direct contacting and insulated. The results demonstrated the process of tuning emission coupled to LSPR via wavelength-dependent photoluminescence intensity in the samples with an insulating spacer. In the direct contact case,the decreased radiative decay rate involves rapid plasmon resonance energy transfer to the perovskite semiconductor and non-radiative energy transfer to metal nanoparticles in the near-field range.

Tunable emission of cadmium-free transition metal(Cu, Mn, Ag) co-doped ZnInS/ZnS core-shell quantum dots

Color tunable quantum dots（QDs） based on the Cu, Mn, Ag co-doped Zn In S core and Zn S outer-shell were synthesized by using an eco-friendly method. Core-shell doped QDs with the average size of 3.85 nm were obtained by using a one-pot synthesis followed by a hot injection with n-dodecanethiol（DDT） and oleylamine（OLA） as stabilizers in oil phase. Cu, Mn and Ag ions were introduced as single-dopant or co-dopants during the synthesis, providing an effective means to control the emission color of the QDs. The as-synthesized QDs showed photoluminescence emission ranging from green（530 nm） to near-red（613 nm）, adjusted by doping components, dopant concentration, and Zn/In ratio. Importantly, quasi-white emission has been achieved by controlling the concentration of co-doped metal ions（Mn, Cu and Ag）. The primary results demonstrated the promising potential of co-doped QDs as alternative materials for future high quality white LED applications.

Luminescent ionic lattice occupation and wide tunable emission spectra of La_(2)MgZrO_(6):Bi^(3+),Eu^(3+)double perovskite phosphors for white light LED

La_(2)Mg_(1-x/2)Zr_(1-x/2)O_(6):xBi^(3+)(x=0.01-0.035,abbreviated as LMZ:Bi^(3+))and La_(2-y)Mg_(0.99)Zr_(0.99)O_(6):0.02Bi^(3+),yEu^(3+)(y=0.1-0.11,abbreviated as LMZ:Bi^(3+),Eu^(3+))double-perovskite phosphors were prepared through high-temperature solid-phase method.The emission spectrum of LMZ:xBi^(3+)(x=0.01-0.035)phosphors excited at 353 nm is asymmetric in the range between 375 and 650 nm,showing strong green light.There are two luminescent centers of[Mg1/Zr2-O_(6)]and[Mg2/Zr1-O_(6)]for Bi^(3+)occupation,which were analyzed through different excitation wavelengths,Gaussian fitting peaks,fluorescence decay curves and Rietveld refinement of powder X-ray diffraction data.Through deep study of the luminescent lattices in the LMZ matrix,the green to blue tunning-emission is observed by different excitation wavelengths.In addition,red emission is obtained by co-doping Bi^(3+)/Eu^(3+),and adjustable emission was investigated by changing the content of Eu^(3+)in the co-doped phosphor formulation,so it is converted from green emission to red emission.The above results demonstrate how to tune emission color by co-doping rare earth ions in the double perovskite phosphor,which is attractive for future applications.

Tunable emission,energy transfer and thermal stability of Ce^(3+),Tb^(3+) co-doped Na_(2)BaCa(PO_(4))_(2) phosphors

A series of single Ce^(3+) doped and Ce^(3+) and Tb^(3+) co-doped Na_(2)BaCa(PO_(4))_(2)(NBCP) phosphors was synthesized by conventional solid-stated reaction method.The crystal structure,luminescence properties,thermal stability and energy transfer were carefully investigated.Ce^(3+) is inferred to substitute the Ba^(2+)site in NBCP lattice.The color-tunable emission from blue to green is observed by adjusting Tb^(3+) concentration among NBCP:0.03 Ce^(3+),yTb^(3+) phosphors.The energy transfer behavior from Ce^(3+) to Tb^(3+) ions is both illustrated by co-doped PL spectra and decay curves.The energy transfer efficiency is as high as 91.5%.The mechanism of energy transfer is resonance type of dipole-dipole transition.In this work,the optimal phosphor exhibits the excellent thermal stability which keeps at 94.9% of that initial value at room temperature when temperature reaches to 150℃.The Ce^(3+) and Tb^(3+) co-doped NBCP phosphor is a promising candidate for the application in the general lighting and display fields.

Low-Frequency Noise in Gate Tunable Topological Insulator Nanowire Field Emission Transistor near the Dirac Point

Low-frequency flicker noise is usually associated with material defects or imperfection of fabrication procedure. Up to now, there is only very limited knowledge about flicker noise of the topological insulator, whose topologically protected conducting surface is theoretically immune to back scattering. To suppress the bulk conductivity we synthesize antimony doped Bi2Se3 nanowires and conduct transport measurements at cryogenic temperatures. The low-frequency current noise measurement shows that the noise amplitude at the high-drain current regime can be described by Hooge＇s empirical relationship, while the noise level is significantly lower than that predicted by Hooge＇s model near the Dirac point. Furthermore, different frequency responses of noise power spectrum density for specific drain currents at the low drain current regime indicate the complex origin of noise sources of topological insulator.

Emission-tunable Ba_(2)Y_(1-x)Sc_(x)NbO_(6):Bi^(3+)(0≤x≤1.0)phosphors for white LEDs

Here,we report a series of Bi^(3+)-doped Ba_(2)Y_(1-x)Sc_(x)NbO_(6)(0≤x≤1.0 mol)phosphors by using the traditional high temperature solid-state reaction.To achieve the structural and photoluminescent(PL)information,several experimental characterizations and theoretical calculations were carried out,including X-ray diffraction(XRD),Rietveld refinement,UV-visible diffuse reflectance and PL spectra,temperature dependent PL spectra,and density functional theo retical(DFT)calculations.The XRD results show that the Bi^(3+)-doped Ba_(2)Y_(1-x)Sc_(x)NbO_(6)samples belong to the double-perovskite phase with a cubic space group of Fm3 m,and the diffraction positions shift toward high diffraction angle when the larger Y^(3+)ions are gradually replaced by the smaller Sc^(3+)ions.In addition,the refined XRD findings show that the Bi^(3+)ions tend to substitute the Y^(3+)and Sc^(3+)sites in the Bi^(3+)-doped Ba_(2)Y_(1-x)Sc_(x)NbO_(6)0<x<1.0 mol)solid solutions.The PL spectra show that the emission positions of the solid solution samples tune from446 to 497 nm with the increase of Sc^(3+) content,which can be attributed to the modification of crystal field strength around Bi^(3+)ions.Moreover,there is energy transfer from the Ba_(2)YNbO_(6)host to Bi^(3+)ions,which is dominated by a resonant type via a dipole-quadrupole(d-q)interaction.The Ba_(2)Y_(0.6)Sc_(0.4)NbO_(6):0.02 molBi^(3+)shows the strongest PL intensity under 365 nm excitation,with the best quantum efficiency(QE)of 68%,and it keeps 60%of the room temperature emission intensity when the temperature increases to 150℃,meaning that the Ba_(2)Y_(0.6)Sc_(0.4)NbO_(6):Bi^(3+)features excellent thermal quenching of luminescence.By combining this optimal sample with a commercial red-emitting Sr_(2)Si_(5)N_(8):Eu^(2+)phosphor,and a commercial 365 nm UV LED chip,a white LED device,with the color temperature(CT)of 3678 K,color rendering index(CRI)of 67.9,and CIE coordinates at(0.371,0.376),is achieved.

Bright and tunable emissive monodisperse CsPbI3@Cs4PbI6 nanocomposites via a precise and controllable dissolution−recrystallization method

Nowadays,due to uncontrolled synthesis and lack of more direct and systematic evidences,the photoluminescence origin of“zero-dimensional”Cs4PbI6 remains great controversy and the luminescence cannot be controlled.Here we propose a controllable dissolution-recrystallization method to synthesize“emissive”and“non-emissive”Cs4PbI6 nanocrystals(NCs)respectively.Through comparing“emissive”and“non-emissive”Cs4PbI6 NCs,it is clearly proved that the visible emission in“emissive”Cs4PbI6 NCs comes from embedded CsPbI3 quantum dots(QDs).It is found for CsPbI3@Cs4PbI6 nanocomposites,methyl acetate(MeAC)and cyclohexane play an important role in dissolution and recrystallization respectively to obtain Cs4PbI6 matrix and CsPbI3 cores.Benefiting from this two-step method,the as-synthesized CsPbI3@Cs4PbI6 nanocomposites with CsPbI3 QDs uniformly distributed in Cs4PbI6 matrix are bright with photoluminescence quantum yield(PLQY)up to 71.4%and exhibit improved stability than CsPbI3 NCs.Moreover,utilizing its formation mechanism,the size of embedded CsPbI3 QDs can be controlled by reasonable designing the“dissolution”process,so that the luminescence of this CsPbI3@Cs4PbI6 nanocomposites can be adjusted in a wide range from green to red(554–630 nm).Our finding not only provides a novel method for synthesizing tunable“emissive”Cs4PbI6 NCs,but also makes clear the photoluminescence origin of“emissive”Cs4PbI6.

Exciplex formation and electroluminescent absorption in ultraviolet organic light-emitting diodes

We investigated the formation of exciplex and electroluminescent absorption in ultraviolet organic light-emitting diodes（UV OLEDs） using different heterojunction structures.It is found that an energy barrier of over 0.3 eV between the emissive layer（EML） and adjacent transport layer facilitates exciplex formation.The electron blocking layer effectively confines electrons in the EML,which contributes to pure UV emission and enhances efficiency.The change in EML thickness generates tunable UV emission from 376 nm to 406 nm.In addition,the UV emission excites low-energy organic function layers and produces photoluminescent emission.In UV OLED,avoiding the exciplex formation and averting light absorption can effectively improve the purity and efficiency.A maximum external quantum efficiency of 1.2%with a UV emission peak of 376 nm is realized.

Emission tunable of Mg_(0.695)Si_(0.695)Al_(1.39)O_(3.65)N_(0.35):Eu^(2+),Mn^(2+) oxynitride phosphors via energy transfer for WLEDs

A series of Eu^(2+)doped and Eu^(2+)/Mn^(2+) co-doped Mg_(0.695)Si_(0.695)Al_(1.39)O_(3.65)N_(0.35)(MSAON) phosphors were synthesized by solid-state reaction at a lower temperature of 1500℃.The crystal morphology and structure of MSAON host were characterized by SEM,TEM and XRD.The quantum yield(QY) for Eu^(2+)doped MSAON phosphors was measured as high as 62%,indicating the excellent luminous efficiency.For the Eu^(2+)/Mn^(2+)co-doped MSAON phosphor,the photoluminescence spectrum and delay curves reveal the efficient energy transfer(ET) process from Eu^(2+)to Mn^(2+)ions.Meanwhile,the corresponding energy transfer efficiency,critical distance and mechanism are discussed in detail.Temperature-dependent emission spectrum shows the thermal and color stabilities.The emission color of MSAON:Eu^(2+),Mn^(2+)phosphors could be tuned from blue through white to red via varying the concentration of Mn^(2+) ions.White-light-emitting diodes(WLEDs) were successfully fabricated by encapsulating the phosphors in nUV LED(365 nm) devices obtaining white light with color rendering index(CRI) as high as 87.7.The results reveal that the MSAON:Eu^(2+),Mn^(2+)phosphors could have potential application in the field of n-UV WLEDs.

可见光到近红外Ⅱ区内宽领域可调发射的芘基共晶

有机材料的可变发光在波导和显示应用方面具有广泛的潜力.然而,基于单一有机分子体系实现从可见光到近红外区域的大范围发光调节仍然是一项挑战.本文介绍了一系列基于芘的同构共晶体,可提供从可见光到近红外Ⅱ区的可调发射.它们的能级是通过引入电荷转移和无氟芳烃-全氟芳烃相互作用而定制的.令人印象深刻的是,这项工作中的有机微晶可以成功地应用于微观层面的多色波导以及宏观层面的二维码显示,为先进的光子学开辟了新的道路.这项工作为获得400至1100 nm的有机晶体提供了一种简单而有效的方法,从而为制造多种光电子学的核心材料提供了可能性.

Solvent-controlled synthesis strategy of multicolor emission carbon dots and its applications in sensing and light-emitting devices

Carbon dots(CDs),as a new kind of carbon-based luminescent nanomaterials,have drawn widespread attention in the fields of fluorescence sensing,optoelectronic devices,and biological imaging.This work uses citric acid(CA)and Nile Blue A(NBA)as precursors.By simply changing the solvent in the reaction,their bandgaps were systematically controlled,thereby successfully obtaining bright blue,yellow and red fluorescence emission CDs(B-,Y-and RCDs).The higher quantum yield(QY)of B-,Y-and RCDs are 64%,57%and 51%,respectively.The selected precursors and different solvents are the key to the formation of three emission CDs.Detailed characterization and density functional theory(DFT)calculations further indicate that the difference in emission color of CDs is due to the size of the sp^(2) conjugate domain.In addition,we used multicolor CDs as fluorescent probes to investigate their performance in detection.Among them,BCDs and YCDs can detect Sudan Red I with high selectivity and sensitivity.In the concentration range of 0 to 80 pM,the detection limits are 56 and 41 nM,respectively.Multicolor emitting phosphors and fluorescent films are also obtained by mixing CDs with other matrices.Using Ultraviolet(UV)chip as the excitation source and combining with multicolor fluorescent film and a certain proportion of B-,Y-,and RCDs/epoxy resin composites,bright monochromatic light-emitting diodes(LEDs)and white LED(WLED)with high color rendering index(CRI)were prepared.The above results indicate that the multicolor CDs prepared by us have great application potential in the fields of food safety control and optical devices.

Tunable luminescence from Ce-doped aluminoborosilicate glasses

A series of aluminoborosilicate glasses were prepared amounts of SiO2, A1203, H3BO3, Na2CO3, and ZrO2 with adding using the melt-quenching technique for mixture of stoichiometric of different amounts of CeO〉 The samples were investigated by means of luminescence spectroscopy. Tunable luminescence from violet to blue/green was observed from these glasses with different Xe-lamp excitation wavelengths ranging from 370 to 480 nm as well as with laser excitation of 266 and 355 nm. Moreover it was found that the possibility of tuning the light by changing of excitation wavelength was not unique. The same effect was observed by adjusting conditions for luminescence measurements as well as under exposure to β-irradiation. The obtained phenomena could be explained taking into account structural characteristics of this glass and it could be concluded that tunable luminescence results from the presence of different Ce-sites the glass matrix. Thus the results suggest that Ce-doped glasses could be considered as conversion materials for blue light-emitting diode chips to generate white light-emitting diodes.

Zn-doping enhances the photoluminescence and stability of PbS quantum dots for in vivo high-resolution imaging in the NIR-II window

Lead sulfide(PbS)quantum dots(QDs)are important near infrared(NIR)luminescent materials with tunable and strong emission covering a broad NIR region.However,their optical properties are quite sensitive to air,water,and high temperature due to the surface oxidation,thus limiting their applications in optoelectronic devices and biological imaging.Herein,a cation-doping strategy is presented to make a series of high-quality Zn-doped PbS QDs with strong emission covering whole second near-infrared window(NIR-II,1,000-1,700 nm).First-principle calculations confirmed that Zn dopants formed dopant states and decreased the recombination energy gap of host PbS.Notably,the Zn dopants significantly improved the quantum yield,photoluminescence lifetime and thermal stability of PbS QDs.Moreover,the PEGylated Zn-doped PbS QDs emitting in the NIR-llb window(1,500-1,700 nm)realized the noninvasive imaging of cerebral vascular of mouse with high resolution,being able to distinguish blood capillary.This material not only provides a new tool for deep tissue fluorescence imaging,but is also promising for the development of other NIR related devices.

Rational design of systematic AIEEgens further modified by substituents from a novel chain structure

The expansion of new structures in aggregation-induced emission/aggregation-induced emission enhancement(AIE/AIEE)systems has attracted persistent attention recently,from which more luminescent functional molecules with characteristic skeletons are derived to satisfy specialized applications.In this study,a series of derivatives cored by tetraphenyl enamine with various terminal groups were designed and synthesized based on a novel p-πconjugate chain structure(–C=C–N–).Experimental and theoretical studies reveal that attaching modified groups to enamine core is decisive to achieve successful conversion from non-luminance to AIEE-activity.Moreover,due to different substituent effect on electronic structure,molecular conformation and molecular packing,diverse enamine compounds exhibited prominent substituent tunable emission properties,realizing regulated AIEE effect and multicolor emitting.These results not only offer a new method to design AIEgens/AIEEgens with p-πconjugate chain structures,but also provide in-depth knowledge for functional modifications of more novel AIE/AIEE units and materials.