Luminescent characteristics of Tm^(3+)/Tb^(3+)/Eu^(3+) tri-doped Na_(5)Y_(9)F_(32) single crystals for white emission with high thermal stability

By using an improved Bridgman method,0.3 mol%Tm^(3+)/0.6 mol%Tb^(3+)/y mol%Eu^(3+)(y=0,0.4,0.6,0.8)doped Na_(5)Y_(9)F_(32)single crystals were prepared.The x-ray diffraction,excitation spectra,emission spectra and fluorescence decay curves were used to explore the crystal structure and optical performance of the obtained samples.When excited by 362 nm light,the cool white emission was realized by Na_(5)Y_(9)F_(32)single crystal triply-doped with 0.3 mol%Tm^(3+)/0.6 mol%Tb^(3+)/0.8 mol%Eu^(3+),in which the Commission Internationale de l’Eclairage(CIE)chromaticity coordinate was(0.2995,0.3298)and the correlated color temperature(CCT)was 6586 K.The integrated normalized emission intensity of the tridoped single crystal at 448 K could keep 62%of that at 298 K.The internal quantum yield(QY)was calculated to be~15.16%by integrating spheres.These results suggested that the single crystals tri-doped with Tm^(3+),Tb^(3+)and Eu^(3+)ions have a promising potential application for white light-emitting diodes(w-LEDs).

White Organic Light Emitting Devices Based on Multiple Emissive Nanolayers

In this paper,a white organic light-emitting device(WOLEDs) with multiple-emissive-layer structure has been fabricated.The device has a simple structure of indium tin oxide(ITO)/NPB(20 nm)//DPVBi(20 nm)/CDBP:x Ir(btp)2acac(10 nm)/Alq3(25 nm)/BCP(5 nm)/Cs F(1 nm)/Al(150 nm)(x= 0.15,2.5 and 3.0 wt%),where NPB and BCP are used as the hole-injecting layer,electron transporting and hole blocking layer,respectively.White light emission was realized in an OLED with 2.5% Ir(btp)2acac doping concentration.The device exhibits peak efficiency of 1.93 cd/A at 9 V and maximum brightness of 7005 cd/m^2 at 14 V.The Commission International de I'Eclairage(CIE)(1931) coordinates of white emission are well within the white zone,which moves from(0.35,0.33) to(0.26,0.30) when the applied voltage is varied from 5 V to 14 V.

Carbon dot-based artificial light-harvesting systems with sequential energy transfer and white light emission for photocatalysis

In this work, we designed and synthesized cationic carbon dots(CDs) with a size distribution of 1.6–3.7 nm, which exhibited dark blue fluorescence in the aqueous solution. Based on its excellent luminescence properties, we used it as an energy donor to construct a sequential artificial light-harvesting system(LHS) by employing the energy-matching dyes eosin Y disodium salt(EY) and sulforhodamine101(SR101), which could regulate the white light emission(Commission Internationale de l'Eclairage(CIE) coordinate:(0.30, 0.31)) with the energy transfer efficiency(ΦET) of 53.9% and 20.0%. Moreover, a single-step artificial LHS with white light emission(0.32, 0.28) can be constructed directly using CDs and dye solvent 43(SR) with ΦETand antenna effect(AE) of 48.8% and 6.5, respectively. More importantly,CDs-based artificial LHSs were firstly used in photocatalytic of α-bromoacetophenone, with a yield of90%. This work not only provides a new strategy for constructing CDs-based LHSs, but also opens up a new application for further applying the energy harvested in CDs-based LHSs to the field of the aqueous solution photocatalysis.

Tunable emission properties of tri-doped Ca_(9)LiY_(2/3)(PO_(4))_(7):Ce^(3+),Tb^(3+),Mn^(2+) phosphors with warm white emitting based on energy transfer

Tri-doped Ca_(9)LiY_(2/3)(PO_(4))_(7):Ce^(3+),Tb^(3+),Mn^(2+)phosphors were prepared by a high-temperature solid state method.Under UV light excitation,Ca_(9)LiY_(2/3)(PO_(4))_(7):Ce^(3+)samples exhibit a broad band ranging from 320 to 500 nm.At 77 K,the emission spectra of Ca_(9)LiY_(2/3)(PO_(4))7:Ce^(3+)samples present two obvious emission peaks,indicating that Ce^(3+)ions occupy two different kinds of lattice sites(Ca(1/2)and Ca(3)),As a good sensitizer for Tb^(3+),Ce^(3+)ions in Ca_(9)LiY_(2/3)(PO_(4))_(7)lattice can effectively transfer part of energy to Tb^(3+),and the energy trans fer mechanism is determined to be dipole-dipole interaction.Consequently,the emitting color for Ce^(3+)and Tb^(3+)co-doped Ca_(9)LiY_(2/3)(PO_(4))_(7)samples can be tuned from bluish violet to green.In order to further enlarge the emission gamut,Mn^(2+)ions as red emission components were added,forming tri-doped single-phase Ca_(9)LiY_(2/3)(PO_(4))_(7):Ce^(3+),Tb^(3+),Mn^(2+)phosphors.The Ca_(9)LiY_(2/3)(PO_(4))_(7):Ce^(3+),Tb^(3+),Mn^(2+)phosphors exhibit tunable emission properties through controlling the relative doping concentration of Ce^(3+),Tb^(3+)and Mn^(2+).Especially,Ca_(9)LiY_(2/3)(PO_(4))_(7):0.09 Ce^(3+),0.12 Tb^(3+),0.30 Mn^(2+)can emit warm white light.The sample shows good thermal stability.At 150℃,the emission intensity for Ce^(3+)(360 nm),Tb^(3+)(545 nm)and Mn^(2+)(655 nm)decreases to 63%,69%,and 72%of its initial intensity,respectively.Moreover,the sample obtains good stability after 10 cycles between room temperature and150℃.

Acid-induced tunable white light emission based on triphenylamine derivatives

A series of triphe nylamine(TPA)derivatives with various substituent groups were prepared and showed different absorption and fluorescence characteristics due to the substituent effect.On account of the existence of pyridine units,these TPA derivatives exhibited acid-induced tunable multicolor fluorescence emission including white light emission.In addition,acid-induced fluorescence regulation of these compounds has been also realized in the solid state,which enable them to be successfully constructed the stimuli-responsive fluorescent films and fluorescent inks for inkjet printing.

High-performance CsPbBr_(3)@Cs_(4)PbBr_(6)/SiO_(2) nanocrystals via double coating layers for white light emission and visible light communication

Owing to their outstanding optoelectronic properties,all-inorganic CsPbBr_(3) perovskite nanocrystals(NCs)are regarded as excellent materials for various optoelectronic applications.Unfortunately,their practical applications are limited by poor stability against water,heat,and polar solvents.Here,we propose a facile synthesis strategy for CsPbBr_(3)@Cs_(4)PbBr_(6) NCs via tetraoctylammonium bromide ligand induction at room temperature.The resulting CsPbBr_(3)@Cs_(4)PbBr_(6) NCs show a high photoluminescence quantum yield of 94%.In order to prevent Cs4PbBr6 from being converted back to CsPbBr_(3) NCs when exposed to water,a second coating layer of SiO2 is formed on the surface of the CsPbBr_(3)@Cs_(4)PbBr_(6) NCs by the facile hydrolysis of tetramethoxysilane.The resulting CsPbBr_(3)@Cs_(4)PbBr_(6)/SiO_(2) NCs with their double coating structure have outstanding stability against not only a polar solvent(ethanol)but also water and heat.The as-prepared CsPbBr_(3)@Cs_(4)PbBr_(6)/SiO_(2) NCs serve as green emitters in efficient white light-emitting diodes(WLEDs)with a high color rendering index(CRI)of 91 and a high power efficiency 59.87 lm W−1.Furthermore,the use of these WLEDs in visible light communication(VLC)results in a maximum rate of 44.53 Mbps,suggesting the great potential of the reported methods and materials for solid-state illumination and VLC.

White light emission from AIE-active luminescent organic materials

Fluorescent organic materials that exhibit unique aggregation-induced emission have been utilized for various applications,including white light emission(WLE).The materials typically rely on composite designs involving a mixture of compounds emitting at different wavelengths of light.To overcome the limitations offered by the design of such composite mixtures,tremendous efforts were also emphasized in developing single-molecule substrates that emit white light.The white light by either method is typically controlled by the solvent polarity,energy and charge transfer,host-guest interactions,gelation,or embedding in the polymer or organic frameworks.This article briefly reviews various molecules exhibiting aggregation-induced emission behavior and emitting white light.

Blue emitting exciplex for yellow and white organic light‑emitting diodes

White organic light-emitting diodes(WOLEDs)have several desirable features,but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures.Herein,we investigate a standard blue emitting hole transporting material(HTM)N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine(NPB)and its exciplex emission upon combining with a suitable electron transporting material(ETM),3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole(TAZ).Blue and yellow OLEDs with simple device structures are developed by using a blend layer,NPB:TAZ,as a blue emitter as well as a host for yellow phosphorescent dopant iridium(III)bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate(PO-01).Strategic device design then exploits the ambipolar charge transport properties of tetracene as a spacer layer to connect these blue and yellow emitting units.The tetracene-linked device demonstrates more promising results compared to those using a conventional charge generation layer(CGL).Judicious choice of the spacer prevents exciton difusion from the blue emitter unit,yet facilitates charge carrier transport to the yellow emitter unit to enable additional exciplex formation.This complementary behavior of the spacer improves the blue emission properties concomitantly yielding reasonable yellow emission.The overall white light emission properties are enhanced,achieving CIE coordinates(0.36,0.39)and color temperature(4643 K)similar to daylight.Employing intermolecular exciplex emission in OLEDs simplifes the device architecture via its dual functionality as a host and as an emitter.

White light luminescence in Dy/Tm co-doped yttria stabilized zirconia single crystals

A series of high quality Dy_(2)O_(3) and Tm_(2)O_(3)co-doped yttria stabilized zirconia(YSZ) single crystals was synthesized.These crystals have a single cubic structure,and exhibit the characteristic of Dy^(3+)(blue and yellow emissions) and Tm^(3+)(blue emission) under excitation with NUV light.Impo rtantly,the hue can be varied between blue and white by modifying the Tm^(3+)/Dy^(3+)ratio.The photoluminescence and decay curves are consistent with the existence of resonance-type energy transfer from Tm^(3+)to Dy^(3+)ions via an electric multipole interaction mechanism.Maximum luminescence intensity is observed in YSZ doped with 0.50 mol% Tm_(2)O_(3) and 0.75 mol% Dy_(2)O_(3),and this sample has CIE coordinates(x = 0.33,y = 0.33) in accordance with those for white chromaticity.Thus,the outstanding luminescence properties of these single crystals suggest potential applications in white light emission devices.

Photoluminescence properties of Tm^(3+)/Tb^(3+)/Sm^(3+) tri-doped Na_(5)Y_(9)F_(32) single crystal with high thermal stability for white light-emitting diodes

A novel Tm^(3+)/Tb^(3+)/Sm^(3+)tri-doped Na_(5)Y_(9)F_(32)single crystal was synthesized by a modified Bridgman method for the propose of white light emitting diodes.The fluorescence spectra of various Sm^(3+)ion concentrations and fixed 0.4 mol%Tm^(3+)and 0.5 mol%Tb^(3+)were measured and studied systematically excited by near-ultraviolet light of 355 nm.The Sm3+ion concentration takes apparent effect on the relative intensity of peaks in the visible region and the color coordinate combining from these emission bands.A near pure white light emission with color coordinates(0.3295,0.3057)and color temperature(5657 K)can be obtained when the concentrations of Tm^(3+),Tb^(3+)and Sm^(3+)ions are 0.4 mol%,0.5 mol%and 0.8 mol%,respectively.Furthermore,the practical down-conversion internal quantum yield was measured by integrating spheres at about 14.39%.The tri-doped Na_(5)Y_(9)F_(32)single crystal shows a high thermal stability inferring from the temperature dependent emission in which the integrated emission intensities are reduced only by^3%with the increase of temperature from 280 to 450 K.The present results demonstrate that the Tm^(3+)/Tb^(3+)/Sm^(3+)tri-doped Na_(5)Y_(9)F_(32)single crystal may provide a promising candidate for white light-emitting diodes,luminescent materials and fluorescent display devices.

Tunable light emission from carbon dots by controlling surface defects

Carbon dots(CDs)are metal-free fluorescent materials that can be used in optical and electronic devices,but few studies have focused on one-step synthesis routes for CDs with tunable color and high photoluminescence quantum yield(PLQY).Herein,CDs with tunable light emission were synthesized using a novel amide-assisted solvothermal approach.The as-prepared CDs were well dispersed and homogeneous,with average diameters of approximately 2.0–4.0 nm,depending on the dopants.Owing to the surface states with different ratios of nitrogen-and oxygen-related species,different CDs can exhibit blue,green,red,or white emission with relatively high PLQYs of 61.6%,41.3%,29.1%and 19.7%,respectively.XPS measurements,in conjunction with DFT calculations,indicate that nitrogen substitution(pyridinic/pyrrolic nitrogen)dominates the blue emission,while introducing oxygen functional groups lowered the LUMO energy level,which resulted in redder emission.In addition,the CDs are demonstrated as a bioimaging probe in both in vitro and in vivo assays,and the white light CDs have been demonstrated to be potential fluorescent materials for white-light-emitting diode(WLED).

Effect of various red phosphorescent dopants in single emissive white phosphorescent organic light-emitting devices

In order to realize single emissive white phosphorescent organic light-emitting devices(PHOLEDs) with three color phosphorescent dopants(red, green, and blue), the energy transfer between the host material and the three dopants, as well as the among the three dopants themselves, should be considered and optimized. To explore the effect of red phosphorescent dopant on the color rendering index(CRI), the authors investigate the wavelength position of the maximum emission peak from three phosphorescent dopants. The CRI and luminous efficiency of white PHOLED in which Ir(pq)_2(αcαc) acts as the red phosphorescent dopant are found to be greater than those of devices prepared using Ir(pig)_3 and Ir(pq)_2(αcαc) as the emission spectrum has a relatively high intensity near the human perception of blue, red, and green wavelengths. Furthermore, we demonstrate that the performance of the three dopants is related to the absorption characteristics of the red phosphorescent dopant.With a maximum emission peak at 600 nm, Ir(pq)_2(αcαc) has a higher intensity in the concave section between 550 and 600 nm seen for red and blue dopants. In addition, the long metal-to-ligand charge transfer(MLCT)absorption tail of Ir(pq)_2(αcαc) overlaps with the emission spectra of the green dopant, enhancing emission. Such energy transfer mechanisms are confirmed to optimize white emission in the single emissive white PHOLEDs.

基于冷却工程对环保型ZnSeTe基量子点的激发态调控

由于材料内部存在高效的非辐射复合,这使得实现高质量的环保量子点仍然具有挑战性.本文中,我们探索了通过冷却工程调节激发态对实现高质量的ZnSeTe核壳量子点的影响.研究发现,超快热载流子俘获和带边载流子俘获是ZnSeTe量子点发射效率低下的主要原因.我们通过设计冷却工程抑制上述过程,并且结合电子和光谱表征分析了其潜在机制.经过冷却优化的ZnSeTe量子点表现出高量子发光效率(>90%)和稳定性,这可与经典的CdSe量子点相媲美.基于这种量子点的白光发光二极管(WLED)表现出优异的光学性能,包括高显色指数(80)和良好的相关色温(7391 K).此外,高性能的WLED还可以用作环保可见光通信.这些结果表明了环保量子点在实际应用中的可行性.