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).

Laser induced broad band anti-Stokes white emission from LiYbF_4 nanocrystals

Spectroscopic properties of tetragonal LiYbF_4 nanocrystals under high dense NIR excitation at vacuum condition were investigated. White, broad band emission covering whole visible part of the spectrum from LiYbF_4 nanocrystals was observed. Its intensity strongly depended on the excitation power, excitation wavelength and ambient pressure. Temperature of the nanocrystals under 975 nm excitation was determined as a function of excitation power. Strong photo-induced current was observed from LiYbF_4 pallet. The emission kinetic was analyzed. The mechanism of the anti-Stokes white emission was discussed in terms of the laser-induced charge transfer emission from Yb^（2＋） states.

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.

Rare Earth Luminescent Materials for White LED Solid State Lighting

Solid-state white LED will be a new generation of energy-saving light source in 21 century. In order to emitting white light, one of important approaches is using luminescence conversion technology with rare earth phosphors, which can be excited by the 460 nm blue light or 400 nm near violet light emitted from the InGaN chip and then emit white light. The rare earths doped phosphors prepared by us such as YAG ： Ce^3＋, Ca1-xSrxS ： Eu^2＋, Ga2S3 ： Eu^2＋, MGa2S4：Eu^2＋ （M = Ca, Sr, Ba）, SrGa2＋xS4＋y ：Eu^2＋,（Ca1 - xSrx ） Se ： Eu^2 ＋ , SrLaGaaS6O ： Eu^2 ＋ , （ M1, M2 ） 10 （PO4）6XE（M1 = Ca, Sr, Ba; Ms = Eu, Mn; X = F, Cl, Br） and NaEu0.92 Sm0.08 （MoO4）5 were reported. They emit blue, green, yellow or red color light. Some white LEDs were made by these phosphors with blue or near violet InGaN chips and their chromaticity coordinate （x, y）, correlated color temperature Tc, and color rendering index Ra are reported.

A porous Eu-PTA/Tb-SSA/ZrO_(2)/ZnZrO_(3) light color adjustable phosphor:Luminescent property and application of warm white LED

Light emitting diode(LED) is the fourth generation lighting source,but it has some shortcomings such as complex chip packaging process and the unbalanced light color of phosphor in long-time application.In this study,a kind of Eu-terephthalic acid/Tb-sulfosalicylate/ZrO_(2)/ZnZrO_(3)(Eu-PTA/Tb-SSA/ZrO_(2)/ZnZrO_(3))phosphor with warm white light emission properties was prepared,and the warm white light LED(wWLEDs) was successfully prepared by encapsulating Eu-PTA/Tb-SSA/ZrO_(2)/ZnZrO_(3) phosphors together with 270 nm UV-chip.The ZrO_(2)/ZnZrO_(3),Tb-SSA/ZrO_(2)/ZnZrO_(3) and Eu-PTA/ZrO_(2)/ZnZrO_(3) samples show blue emission,green emission and red emission under deep ultraviolet(UV,270 nm) excitation,respectively.The Tb-SSA and Eu-PTA are co-doped into ZrO_(2)/ZnZrO_(3) matrix with blue emission to achieve the warm white light emission,and the light color can be adjusted by controlling the doping amount of Eu^(3+)-and Tb^(3+).Through the excitation method of single-component phosphor by the single chip,the complex chip packaging process of w-LED can be solved.By doping rare earth organic complexes into porous ZrO_(2)/ZnZrO_(3) matrix,the problems of the light color unbalanced of phosphor and the low luminescence intensity of rare earth doped metal oxides composites can be solved.

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.

White light emission of Eu^(3+)/Ag co-doped Y_2Si_2O_7

The Eu^3＋/Ag co-doped rare earth disilicate Y2Si2O7 microcrystal was synthesized by sol-gel method. Through controlling the thermal treatment process of YzSi2OT：EU3＋/Ag precursor, various phases （amorphous, α, β, γ, δ） were prepared. White light emis- sion was observed under UV light excitation in the samples heavily doped with Ag. The white light was realized by combining the intense red emission of Eu3＋, the green emission attributed to the very small molecule-like, non-plasmonic Ag particles （ML-Ag-particles）, and the blue emission due to Ag ions. Results demonstrated that Eu3＋/Ag co-doped Y2Si207 microcrystal could be potentially applied as white light emission phosphors for UV LED chips.

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 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.

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.

Controlling molecular assembly on time scale:Time-dependent multicolor fluorescence for information encryption

Dynamic assembly on time scale is common in biological systems but rare for artificial materials,especially for smart luminescent materials.Programming molecular assembly in a spatio-temporal manner and resulting in white-light-including multicolor fluorescence with time-dynamic features remains challenging.Herein,controlling molecular assembly on time scale is achieved by integrating a pH-responsive motif to a transient alkaline solution which is fabricated by activators(NaOH)and deactivators(esters),leading to automatic assembly on time scale and time-dependent multicolor fluorescence changing from blue to white and yellow.The kinetics of the assembly process is dependent on the ester hydrolysis process,which can be controlled by varying ester concentrations,temperature,initial pH,stirring rate and ester structures.This dynamic fluorescent system can be further developed for intelligent fluorescent materials such as fluorescent ink,three-dimension(3D)codes and even four-dimension(4D)codes,exhibiting a promising potential for information encryption.

Highly Efficient Hybrid White Tandem Organic Light-Emitting Diodes with MoO3 Layer

Electroluminescence （EL） characteristics have been studied for a hybrid tandem white organic light emitting diode （OLED） with a blue emitting fluorescent EL1 unit based on BCzVBi and a yellow emitting phosphorescent EL2 unit based on （fbi）2Ir（acac）, where a MoO3 layer is inserted between EL1 and EL2 units as charge generation layer （CGL）. Maximum current and power efficiencies of 68.1 cd/A and 29.2 lm/W were obtained, respectively, while the current and power efficiencies at luminance of 1000 cd/m2 were 68.0 cd/A and 24.6 lm/W. The yellow emission appears from about 4.5 V firstly, while the blue emission starts to appear from about 5.4 V. It was found that charge generation from CGL of MoO3/NPB bilayer occurred at high voltages of above 5.4 V but not at low voltages below 5.2 V.

Tuning red-green-white up-conversion color in nano NaYF_4:Er/Yb phosphor

The possibility of ttming between red, green and broadband white color of up-conversion was demonstrated in thermally 450 ℃ treated Yb/Er co-doped nano NaYF4 phosphor. The color variability was studied by means of power dependence of luminescence, which exhibited unusual behavior. Large hysteresis, as well as discrepancy from a power law indicated the important role the increased heating played during the up-conversion in nano-sized materials.

The origins of the broadband photoluminescence from carbon nitrides and applications to white light emitting

Carbon nitrides synthesized by thermal polycondensation of melamine at 700 ~C exhibit photoluminescence （PL） ranging from 400 to 650 nm. This broad PL is attributed to band to band transitions and bandtail transitions of lone pair （LP） states of intra-tri-s-triazine and inter-tri-s-triazine nitrogens. The proposed PL mechanism is further confirmed by diffusion reflectance spectroscopy, as well as time-resolved and temperature-dependent PL. This intense fluorescence is stable at different pH and resistant to UV exposure, suggesting that this inexpensive broadband luminescent material could be significant for white- light-emitting （WLE） applications. Thus, quasi-WLE films and membranes with designed patterns are fabricated by embedding the carbon nitrides into polymethyl methacrylate. Moreover, even broader PL （400 to 740 nm） is acquired in com- posite films composed of carbon nitrides, further suggesting that the carbon nitrides are robust candidates for WLE.

Growth and Optical Spectra of Tb^(3+)/Eu^(3+) Co-doped Cubic NaYF_4 Single Crystal for White Light Emitting Diode

High quality Tb^3＋/Eu^3＋ co-doped cubic NaYF 4 single crystal in the size of Φ1.0 cm×6.6 cm was grown by a modified Bridgman method using KF as assistant flux for NaF-YF 3 system under the condition of completely closed Pt crucible.A white light emission from the combination of the violet-blue,blue,green,orange,and red lights with chromaticity coordinates of x = 0.3107,y = 0.3274,correlated color temperature of T c = 6637 K,color rendering index of R a = 83,and color quality scale of Q a = 82 could be obtained from 1.51 mol%Tb^3＋ and 1.42 mol%Eu^3＋ co-doped cubic NaYF 4 single crystal when being excited by a 369 nm light.This indicates that Tb^3＋/Eu^3＋）co-doped cubic NaYF 4 single crystal has a potential application in white light emitting diode excited by ultraviolet light.

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).