Solid‐State Carbon Dots with Efficient Cyan Emission towards White Light‐Emitting Diodes

Efficient cyan‐emitting solid carbon dots (CDs) were synthesized via a one‐pot hydrothermal method. The obtained solid CDs show a broad absorption from 270–460 nm with a maximum around 400 nm, and emit intense cyan light around 500 nm with an internal photoluminescence quantum efficiency of 34.1 % under 400 nm excitation. The emission maximum of the solid CDs remains unchanged under 320–400 nm excitations. Compared with dilute aqueous of CDs (2.5 mg mL^?1), the emission of solid CDs shows an obvious red‐shift of 50 nm. The red‐shift is caused by resonant energy transfer due to larger spectral overlap and smaller interparticle distance, together with a new surface state caused by aggregation in solid CDs. A lamp with white LEDs was fabricated by dropping a mixture of solid CDs, CaAlSiN₃:Eu²⁺ and silicon resin on the top of a near‐ultraviolet LED chip. Under an operating current of 20 mA, the as‐fabricated white LED generates a high‐quality, warm white light with a color rendering index of 86.1, a color temperature of 4340 K, and a luminescence efficiency of 31.3 lm W^?1.     

One‐pot synthesis of carbon dots@ZrO2 nanoparticles with tunable solid‐state fluorescence

In recent years, fluorescent carbon dots (CDs) have been developed and showed potential applications in biomedical imaging and light‐emitting diodes (LEDs) for their excellent fluorescent properties. However, it still remains a challenge to incorporate fluorescent CDs into the host matrix in situ to overcome their serious self‐quenching. Herein, a one‐pot hydrothermal method is used to prepare nano‐zirconia with CDs (CDs@ZrO₂) nanoparticles. During the reaction, CDs and nano‐zirconia are generated simultaneously and connected with silane coupling agent. The CDs@ZrO₂ nanoparticles exhibit tunable emission wavelength from 450 to 535 nm emission by regulating the content of citric acid in the feed. The quantum yield of the CDs@ZrO₂ is up to 23.8%. Furthermore, the CDs@ZrO₂ nanoparticles with regulable fluorescence emission can be used for the fluorescent material to prepare white LEDs. The prepared LED has significant white light emission with color coordinates of (0.30, 0.37) and its color rendering index (CRI) is 67.1. In summary, we have developed the solid‐state CDs@ZrO₂ nanoparticles with tunable emission by a valuable strategy, that is, one‐pot method, for white LEDs.     

Red,Green, and Blue Luminescence by Carbon Dots: Full‐Color Emission Tuning and Multicolor Cellular Imaging

A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a single ultraviolet‐light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up‐conversion (UC)PL of these CDs is also observed. Moreover, flexible full‐color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light‐emitting diodes, full‐color displays, and multiplexed (UC)PL bioimaging.     

Red,Green, and Blue Luminescence by Carbon Dots: Full‐Color Emission Tuning and Multicolor Cellular Imaging

A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a single ultraviolet‐light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up‐conversion (UC)PL of these CDs is also observed. Moreover, flexible full‐color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light‐emitting diodes, full‐color displays, and multiplexed (UC)PL bioimaging.     

Doped Lead Halide White Phosphors for Very High Efficiency and Ultra‐High Color Rendering

Near‐UV‐pumped white‐light‐emitting diodes with ultra‐high color rendering and decreased blue‐light emission is highly desirable. However, discovering a single‐phase white light emitter with such characteristics remains challenging. Herein, we demonstrate that Mn doping as low as 0.027 % in the hybrid post‐perovskite type (TDMP)PbBr₄ (TDMP=trans‐2,5‐dimethylpiperaziniium) enables to achieve a bright pure white emission replicating the spectrum of the sun's rays. Thus, a white phosphor exhibiting an emission with CIE coordinates (0.330, 0.365), a high photoluminescence quantum yield of 60 % (new record for white light emission of hybrid lead halides), and an ultra‐high color rendering index (CRI=96, R9=91.8), corresponding to the record value for a single phase emitter was obtained. The investigation of the photoluminescence properties revealed how free excitons, self‐trapped excitons, and low amount of Mn dopants are coupled to give rise to such pure white emission.     

Carbon Dots with Dual‐Emissive,Robust, and Aggregation‐Induced Room‐Temperature Phosphorescence Characteristics

Carbon dots (CDs) with dual‐emissive, robust, and aggregation‐induced RTP characteristics are reported for the first time. The TA‐CDs are prepared via hydrothermal treatment of trimellitic acid and exhibit unique white prompt and yellow RTP emissions in solid state under UV excitation (365 nm) on and off, respectively. The yellow RTP emission of TA‐CDs powder should be resulted from the formation of a new excited triplet state due to their aggregation, and the white prompt emission is due to their blue fluorescence and yellow RTP dual‐emissive nature. The RTP emission of TA‐CDs powder was highly stable under grinding, which is very rare amongst traditional pure organic RTP materials. To employ the unique characteristics of TA‐CDs, advanced anti‐counterfeiting and information encryption methodologies (water‐stimuli‐response producing RTP) were preliminarily investigated.     

Zero‐Dimensional Hybrid Cd‐Based Perovskites with Broadband Bluish White‐Light Emissions

Recently, low‐dimensional organic‐inorganic hybrid metal halide perovskites acting as single‐component white‐light emitting materials have attracted extensive attention, but most studies concentrate on hybrid lead perovskites. Herein, we present two isomorphic zero‐dimensional (0D) hybrid cadmium perovskites, (HMEDA)CdX₄ (HMEDA=hexamethylenediamine, X=Cl ( 1 ), Br ( 2 )), which contain isolated [CdX₄]^2? anions separated by [HMEDA]²⁺ cations. Under UV light excitation, both compounds display broadband bluish white‐light emission (515 nm for 1 and 445 nm for 2 ) covering the entire visible light spectrum with sufficient photophysical stabilities. Remarkably, compound 2 shows a high color rendering index (CRI) of 83 enabling it as a promising candidate for single‐component WLED applications. Based on the temperature‐dependent, powder‐dependent and time‐resolved PL measurements as well as other detailed studies, the broadband light emissions are attributed to self‐trapped excitons stemming from the strong electron‐phonon coupling.     

A Novel trans‐1‐(9‐Anthryl)‐2‐phenylethene Derivative Containing a Phenanthroimidazole Unit for Application in Organic Light‐Emitting Diodes

Aryl‐substituted phenanthroimidazoles (PIs) have attracted tremendous attention in the field of organic light‐emitting diodes (OLEDs), because they are simple to synthesize and have excellent thermal properties, high photoluminescence quantum yields (PLQYs), and bipolar properties. Herein, a novel blue–green emitting material, (E)‐2‐{4′‐[2‐(anthracen‐9‐yl)vinyl]‐[1,1′‐biphenyl]‐4‐yl}‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (APE‐PPI), containing a t‐APE [1‐(9‐anthryl)‐2‐phenylethene] core and a PI moiety was designed and synthesized. Owing to the PI skeleton, APE‐PPI possesses high thermal stability and a high PLQY, and the compound exhibits bipolar transporting characteristics, which were identified by single‐carrier devices. Nondoped blue–green OLEDs with APE‐PPI as the emitting layer show emission at λ=508 nm, a full width at half maximum of 82 nm, a maximum brightness of 9042 cd m^?2, a maximum current efficiency of 2.14 cd A^?1, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.55). Furthermore, a white OLED (WOLED) was fabricated by employing APE‐PPI as the blue–green emitting layer and 4‐(dicyanomethylene)‐2‐tert‐butyl‐6‐(1,1,7,7‐tetramethyljulolidin‐4‐yl‐vinyl)‐4H‐pyran (DCJTB) doped in tris‐(8‐hydroxyquinolinato)aluminum (Alq₃) as the red–green emitting layer. This WOLED exhibited a maximum brightness of 10029 cd m^?2, a maximum current efficiency of 16.05 cd A^?1, CIE coordinates of (0.47, 0.47), and a color rendering index (CRI) of 85. The high performance of APE‐PPI‐based devices suggests that the t‐APE and PI combination can potentially be used to synthesize efficient electroluminescent materials for WOLEDs.     

Luminescence Color‐Tuning through Polymorph Doping: Preparation of a White‐Emitting Solid from a Single Gold(I)–Isocyanide Complex by Simple Precipitation

We report the luminescent color tuning of a new complex, 2‐benzothiophenyl(4‐methoxyphenyl isocyanide)gold(I) ( 1 ), by using a new “polymorph doping” approach. The slow crystallization of the complex 1 afforded three different pure polymorphic crystals with blue, green, and orange emission under UV‐light irradiation. The crystal structures of pure polymorphs of 1 were investigated in detail by means of single‐crystal X‐ray analyses. Theoretical calculations based on the single‐crystal structures provided qualitative explanation of the difference in the excited energy‐levels of the three polymorphs of 1 . In sharp contrast, the rapid precipitation of 1 , with the optimized conditions reproducibly afforded homogeneous powder materials showing solid‐state white‐emission with Commission Internationale de l’Éclairage (CIE) 1931 chromaticity coordinates of (0.33, 0.35), which is similar to pure white. New “polymorphic doping” has been revealed to be critical to this white emission through spectroscopic and X‐ray diffraction analyses. The coexistence of the multiple polymorphs of 1 within the homogeneous powder materials and the ideal mixing of multiple luminescent colors gave its white emission accompanied with energy transfer from the predominant green‐emitting polymorph to the minor orange‐emitting polymorph.     

Site‐Selective Occupancy of Eu2+ Toward Blue‐Light‐Excited Red Emission in a Rb3YSi2O7:Eu Phosphor

Establishing an effective design principle in solid‐state materials for a blue‐light‐excited Eu²⁺‐doped red‐emitting oxide‐based phosphors remains one of the significant challenges for white light‐emitting diodes (WLEDs). Selective occupation of Eu²⁺ in inorganic polyhedra with small coordination numbers results in broad‐band red emission as a result of enhanced crystal‐field splitting of 5d levels. Rb₃YSi₂O₇:Eu exhibits a broad emission band at λ_max=622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu²⁺ ions preferably occupy RbO₆ and YO₆ polyhedra and show the characteristic red emission band of Eu²⁺. The excellent thermal quenching resistance, high color‐rendering index R_a (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare‐earth phosphors is an effective strategy to target tailored optical performance.     

Efficient White‐Light Generation from Ionically Self‐Assembled Triply‐Fluorescent Organic Nanoparticles

Low cost, simple, and environmentally friendly strategies for white‐light generation which do not require rare‐earth phosphors or other toxic or elementally scare species remain an essentially unmet challenge. Progress in the area of all‐organic approaches is highly sought, single molecular systems remaining a particular challenge. Taking inspiration from the designer nature of ionic‐liquid chemistry, we now introduce a new strategy toward white‐light emission based on the facile generation of nanoparticles comprising three different fluorophores assembled in a well‐defined stoichiometry purely through electrostatic interactions. The building blocks consist of the fluorophores aminopyrene, fluorescein, and rhodamine 6G which represent blue, green, and red‐emitting species, respectively. Spherical nanoparticles 16(±5) nm in size were prepared which display bright white‐light emission with high fluorescence quantum efficiency (26 %) and color coordinate at (0.29, 0.38) which lie in close proximity to pure white light (0.33, 0.33). It is noteworthy that this same fluorophore mixture in free solution yields only blue emission. Density functional theory calculations reveal H‐bond and ground‐state proton transfer mediated absolute non‐parallel orientation of the constituent units which result in frustrated energy transfer, giving rise to emission from the individual centers and concomitant white‐light emission.     

Ultra‐Narrow‐Band Blue‐Emitting Oxoberyllates AELi2[Be4O6]:Eu2+ (AE=Sr,Ba) Paving the Way to Efficient RGB pc‐LEDs

Highly efficient phosphor‐converted light‐emitting diodes (pc‐LEDs) are popular in lighting and high‐tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra‐narrow band blue emitting oxoberyllates AELi₂[Be₄O₆]:Eu²⁺ (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi₂[(Al₂Si₂)N₆]:Eu²⁺. The oxoberyllates’ extremely small Stokes shift and unprecedented ultra‐narrow band blue emission with fwhm ≈25 nm (≈1200 cm^?1) at λ_em=454–456 nm result from its rigid, highly condensed tetrahedra network. AELi₂[Be₄O₆]:Eu²⁺ allows for using short‐wavelength blue LEDs (λ_em<440 nm) for efficient excitation of the ultra‐narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.     

Judicious Choice of N‐Heterocycles for the Realization of Sky‐Blue‐ to Green‐Emitting Carbazolylgold(III) C^C^N Complexes and Their Applications for Organic Light‐Emitting Devices

A new class of sky‐blue‐ to green‐emitting carbazolylgold(III) C^C^N complexes containing pyrazole or benzimidazole moieties has been successfully designed and synthesized. Through the judicious choice of the N‐heterocycles in the cyclometalating ligand and the tailor‐made carbazole moieties, maximum photoluminescence quantum yields of 0.52 and 0.39 have been realized in the green‐ and sky‐blue‐emitting complexes, respectively. Solution‐processed and vacuum‐deposited organic light‐emitting devices (OLEDs) based on the benzimidazole‐containing complexes have been prepared. The sky‐blue‐emitting device shows an emission peaking at 484 nm with a narrow full‐width at half‐maximum of 57 nm (2244 cm^?1), demonstrating the potential of this class of complexes in the application of OLEDs with high color purity. In addition, high maximum external quantum efficiencies of 12.3 % and a long operational half‐lifetime of over 5300 h at 100 cd m^?2 have been achieved in the vacuum‐deposited green‐emitting devices.     

A Novel White Light Emitting Long-lasting Phosphor

A novel white light emitting long-lasting phosphor Cd1-xDyxSiO3 is reported in this letterThe Dy^3 doped CdSiO3 phosphor emits white light. The phosphorescence can be seen with the naked eye in the dark clearly even after the 254nm UV irradiation have been removed for about 30min. In the emission spectrum of 5% Dy^3 doped CdSiO3 phosphor, there are two emission peaks of Dy^3 , 580nm (^4F9/2→^6H13/2) and 486nm (^4F9/2→^6H15/2), as well as a broad band emission located at about 410nm. All the three emissions form a white light with CIE chromaticity coordinates x=0.3874, y=0.3760 and the color temperature is 4000 K under 254 nm excitation. It indicated that this phosphor is a promising new luminescent material for practice application.     

White‐Light Emission Strategy of a Single Organic Compound with Aggregation‐Induced Emission and Delayed Fluorescence Properties

A novel white‐light‐emitting organic molecule, which consists of carbazolyl‐ and phenothiazinyl‐substituted benzophenone (OPC) and exhibits aggregation‐induced emission‐delayed fluorescence (AIE‐DF) and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non‐doped powder, which presented white‐emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor–acceptor–donor′ (D‐A‐D′) type of OPC exhibits an accurate inherited relationship from dicarbazolyl‐substituted benzophenone (O2C, D‐A‐D) and diphenothiazinyl‐substituted benzophenone (O2P, D′‐A‐D′). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white‐light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE‐DF white‐light‐emitting organic molecules.     

Pure white‐light‐emitting diodes from phosphorescent single polymer systems

New white polymeric light‐emitting diodes from phosphorescent single polymer systems have been developed using a blue‐light‐emitting fluorene monomer copolymerized with a red‐light‐emitting phosphorescent dye, and end‐capped with a green‐light‐emission dye. All of the copolymers have good thermal stability with 5% weight loss temperatures at 380–413 °C and glass transition temperatures at 75–137 °C. We obtained white‐light‐emission devices by adjusting the molar ratio of the comonomers with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid)/polyvinylcarbazole (PVK)/emission layer/Ca/Ag. The highest brightness in such a device configuration is 300 cd/m² at a current density of 2900 A/m² with high white color quality (Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.34)). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 464–472, 2008     

Hue‐ and Chromaticity‐Based Exploration of Surface Complexation‐Induced Tunable Emission from Non‐Luminescent Quantum Dots

Herein we report the use of a hue parameter of HSV (Hue, Saturation and Value) color space—in combination with chromaticity color coordinates—for exploring the complexation‐induced luminescence color changes, ranging from blue to green to yellow to white, from a non‐luminescent Fe‐doped ZnS quantum dot (QD). Importantly, the surface complexation reaction helped a presynthesized non‐luminescent Fe‐doped ZnS QD to glow with different luminescence colors (such as blue, cyan, green, greenish‐yellow, yellow) by virtue of the formation of various luminescent inorganic complexes (using different external organic ligands), while the simultaneous blue‐ and yellow‐emitting complex formation on the surface of non‐luminescent Fe‐doped ZnS QD led to the generation of white light emission, with a hue mean value of 85 and a chromaticity of (0.28,0.33). Furthermore, the surface complexation‐assisted incorporation of luminescence properties to a non‐luminescent QD not only overcomes their restricted luminescence‐based applications such as light‐emitting, biological and sensing applications but also bring newer avenues towards unravelling the surface chemistry between QDs and inorganic complexes and the advantage of having an inorganic complex with QD for their aforementioned useful applications.     

新型全色发光材料NaCaPO_4:Dy~(3+)制备及发光性能

釆用高温固相法制备了NaCaPO4∶Dy3+系列样品,并在紫外(UV)及真空紫外(VUV)区域研究了系列样品的发光性能.紫外激发光谱显示在350nm处有最强的激发峰,可以有效地吸收紫外光并将其转化为可见光.真空紫外激发光谱表明,NaCaPO4∶Dy3+能有效地吸收无汞荧光灯的激发源并将其转化为可见光.系列样品发光均呈现为白色,这种材料有潜力作为全色显示材料应用于发光二极管(LED)和无汞荧光灯中.     

High red,green, and blue color purity electroluminescence from MEH‐PPV and polyalkyfluorenes‐based bright white polymer light emitting displays

A series of white polymer light emitting displays (PLEDs) based on a polymer blend of polyalkylfluorenes and poly(2‐methoxy‐5,2′‐ethyl‐hexyloxy‐1,4‐phenylene vinylene) (MEH‐PPV) was developed. MEH‐PPV or red light emitting alkyfluorene copolymer (PFR) was blended with blue light emitting alkyfluorene copolymer (PFB), and MEH‐PPV was blended with both green light emitting alkyfluorene copolymer (PFG) and PFB to generate white light emission PLEDs. Low turn on voltage (2.7 V), high brightness (12,149 nits), high efficiency (4.0 cd/A, 4.0 lm/W), and good color purity (Commission Internationale de L'Eclairage (CIE_x,y) co‐ordinates (0.32, 0.34)) were obtained for the white PLEDs based on the PFB and MEH‐PPV polymer blend. Exciplex formation in the interface between PFR and PFB induced a new green emission peak for these two components based white PLEDs. As a result, strong white emission (4078 nits) was obtained by mixing the red, green, and blue (RGB) three primary colors. High color purity of blue (CIE, x = 0.14, y = 0.08), green (CIE, x = 0.32, y = 0.64) and red (CIE, x = 0.67, y = 0.33) emissions was achieved for white PLEDs combining with dielectric interference color‐filters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 330–341, 2007     

Aggregation‐Induced Delayed Fluorescence Luminogens for Efficient Organic Light‐Emitting Diodes

Aggregation‐induced delayed fluorescence (AIDF) can be regarded as a special case of aggregation‐induced emission (AIE). Luminogens with AIDF can simultaneously emit strongly in solid state and fully utilize the singlet and triplet excitons in organic light‐emitting diodes (OLEDs). In this work, two new AIDF luminogens, DMF‐BP‐DMAC and DPF‐BP‐DMAC, with an asymmetric D–A–D′ structure, are designed and synthesized. The characteristics of both luminogens are systematically investigated, including single crystal structures, theoretical calculations, photophysical properties and thermal stabilities. Inspired by their AIDF nature, the green‐emission non‐doped OLEDs based on them are fabricated, which afford good electroluminescence performances, with low turn‐on voltages of 2.8 V, high luminance of 52560 cd m^?2, high efficiencies of up to 14.4 %, 42.3 cd A^?1 and 30.2 lm W^?1, and very small efficiency roll‐off. The results strongly indicate the bright future of non‐doped OLEDs on the basis of robust AIDF luminogens.