Simultaneous Long‐Persistent Blue Luminescence and High Quantum Yield within 2D Organic–Metal Halide Perovskite Micro/Nanosheets

Molecular solid‐state materials with long‐lived luminescence (such as thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) systems) are promising for display, sensoring, and bio‐imaging applications. However, the design of such materials that exhibit both long luminescent lifetime and high solid‐state emissive efficiency remains an open challenge. Two‐dimensional (2D) organic–metal halide perovskite materials have a high blue‐emitting quantum yield of up to 63.55 % and ultralong TADF lifetime of 103.12 ms at ambient temperature and atmosphere. Our design leverages the combined influences of a 2D space/electronic confinement effect and a modest heavy‐atom tuning strategy. Photophysical studies and calculations reveal that the enhanced quantum yield is due to the rigid laminate structure of perovskites, which can effectively inhibit the non‐radiative decay of excitons.     

Yb:Er:Tm:LiTaO3的上转换发白光性能研究

980 nm脉冲激光激发下,首次通过高温固相法制备Yb(10%):Er(1%):Tm(1%):LiTaO3(摩尔分数)多晶粉并实现室温上转换白光.X射线粉末衍射测试结果表明,Yb:Er:Tm:LiTaO3中的掺杂离子并没有改变晶格结构,以取代的方式存在于钽酸锂晶格中.结合功率曲线测试结果和上转换机制研究发现,产生上转换蓝光的Tm3+离子1G4态的布居主要来自双光子同时吸收过程.而单光子上转换输出的红光,则由Tm3+和Er3+离子之间的交叉弛豫过程产生,即3F2/3(Tm3+)+4I15/2(Er3+)→3H6(Tm3+)+4I9/2(Er3+).上转换绿光来源于Yb/Er离子对的二次能量传递.     

Luminescence of PbCl2 and PbBr2 single crystals. III. The blue and violet luminescence; Mechanism of energy transport

The results of the decay time, quantum efficiency and temperature dependence measurements of the uv, blue and red luminescence of PbCl₂ and PbBr₂ are reported. The blue luminescence is associated with a charge transfer transition of the halide ion. PbCl₂ crystals also show a violet luminescence at temperatures lower than 30 K. We tentatively assume that the violet emission, like the uv emission is due to recombination of ³P₁ cation excitons. The excitation of the blue and red luminescence of both lead halides in the energy region of the ³P₁ cation exciton absorption band occurs by transport of excitation energy. We arrive at the conclusion that the excitation energy is transferred nonradiatively from the ³P₁ state of the exciton to the excited state of the centers responsible for the blue and red emission.     

Blue phosphorescent Zn(II) and orange phosphorescent Pt(II) complexes of 4,4'-diphenyl-6,6'-dimethyl-2,2'-bipyrimidine

To investigate the different phosphorescent promoting effects of organic emitters by various metal centers, a new ligand, 4,4'-diphenyl-6,6'-dimethyl-2,2'-bipyrimidine (pmbp), and its Zn(II), Hg(II), and Pt(II) complexes, [Zn(pmbp)(2)](ClO(4))(2)(1), Pt(pmbp)Ph(2)(2), Zn(pmbp)Cl(2)(3), and Hg(pmbp)Cl(2)(4) were synthesized. Their structures were determined by single crystal X-ray diffraction. The zinc complexes 1 and 3 exhibit blue luminescence in the solid state at ambient temperature, but the mercury complex 4 is not luminescent. At 77 K, both pmbp and complex have blue emissions in MeOH solutions, which were demonstrated to be phosphorescence by their long decay lifetime (micros). By comparing the luminescent properties of the free ligand and the complex, we concluded that the phosphorescence of originates from ligand centered pi --> pi* transitions. Complex 2 exhibits orange luminescence both in CH(2)Cl(2) solution at 77 K and in the solid state at ambient temperature, which was assigned to metal-to-ligand [d(M) --> pi*(pmbp)] charge transfer (MLCT). The different origin of luminescence is responsible for the different luminescent color of the Zn(II) and Pt(II) complexes.     

Reversible three-state switching of luminescence: a new twist to electro- and photochromic behavior

The fully reversible three-state blue/red/off emission from photo-/electrochromic substituted bis-thiaxanthylidenes is reported. The blue luminescence of the most stable (anti-folded) conformer of dimethyl- and dimethoxy-bis-thiaxanthylidene can be switched off by photochemical conversion to the meta-stable (syn-folded) conformer and switched on again by thermal reversion to the anti-folded state. The red luminescence of the bis-thiaxanthylium dication can be switched on by oxidation at approximately 1.0 and 1.2 V vs SCE of the syn- and anti-folded conformers respectively and switched off or to blue by reduction at approximately 0.35 V vs SCE.     

Highly efficient non-doped blue fluorescent OLEDs with low efficiency roll-off based on hybridized local and charge transfer excited state emitters

Designing a donor–acceptor (D–A) molecule with a hybridized local and charge transfer (HLCT) excited state is a very effective strategy for producing an organic light-emitting diode (OLED) with a high exciton utilization efficiency and external quantum efficiency. Herein, a novel twisting D–π–A fluorescent molecule (triphenylamine–anthracene–phenanthroimidazole; TPAAnPI) is designed and synthesized. The excited state properties of the TPAAnPI investigated through photophysical experiments and density functional theory (DFT) analysis reveal that its fluorescence is due to the HLCT excited state. The optimized non-doped blue OLED using TPAAnPI as a light-emitting layer exhibits a novel blue emission with an electroluminescence (EL) peak at 470 nm, corresponding to the Commission International de L''Eclairage (CIE) coordinates of (0.15, 0.22). A fabricated device termed Device II exhibits a maximum current efficiency of 18.09 cd A⁻¹, power efficiency of 12.35 lm W⁻¹, luminescence of ≈29 900 cd cm⁻², and external quantum efficiency (EQE) of 11.47%, corresponding to a high exciton utilization efficiency of 91%. Its EQE remains as high as 9.70% at a luminescence of 1000 cd m⁻² with a low efficiency roll-off of 15%. These results are among the best for HLCT blue-emitting materials involved in non-doped blue fluorescent OLEDs. The performance of Device II highlights a great industrial application potential for the TPAAnPI molecule.

A new pure fluorescent blue HLCT-emitter was designed and synthesized. Highly efficient non-doped blue OLEDs with low efficiency roll-off were achieved.     

PDP用纳米BaMgAl10O17:Eu荧光粉的燃烧合成及发光性能

采用溶液燃烧合成法直接合成了PDP用纳米BaMgAl10O17∶Eu(BAM)荧光粉, 并对产物进行了XRD、TEM分析和发光性能测试. 结果表明, 合成产物由单一的BAM组成, 且结晶完好, 不存在位错、孪晶等缺陷；BAM颗粒近似球形, 平均粒径约为20 nm；在334 nm UV光激发下, 样品的发射峰值波长为450 nm, 归属于Eu2+离子的4f 65d→ 4f 7(8S7/2)宽带允许跃迁, 与稀土三基色荧光材料中的蓝色组分发光完全一致. 与高温固相法相比, 燃烧合成法具有合成温度低, 反应时间短, 所得产物纯净且颗粒细小, 发光强度高等优点.     

Sensitization of Tb<Superscript>3+</Superscript> luminescence with polypyridyl ligands in a nafion membrane

Perfluorosulfonic membranes were modified by terbium(III) polypyridyl complexes by ionexchange sorption of cations followed by addition of ligands. The luminescence sensitization degree is compared with the state of ligands in the grafted complexes. In the case of the terbium(III) 4,7-diphenylphenanthroline complex, strong blue luminescence of the ligand is observed, along with radiation transitions of the cation. The character of luminescence quenching in modified membranes in a wet medium is determined by the ability of ligands to prevent terbium from adsorbing water molecules.     

Composition-tunable Zn(x)Cd(1-x)Se nanocrystals with high luminescence and stability

High-quality Zn(x)Cd(1-x)Se nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals. With increasing Zn content, a composition-tunable emission across most of the visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. The photoluminescence (PL) properties for the obtained Zn(x)Cd(1-x)Se nanocrystals (PL efficiency of 70-85%, fwhm = 22-30 nm) are comparable to those for the best reported CdSe-based QDs. In particular, they also have good PL properties in the blue spectral range. Moreover, the alloy nanocrystals can retain their high luminescence (PL efficiency of over 40%) when dispersed in aqueous solutions and maintain a symmetric peak shape and spectral position under rigorous experimental conditions. A rapid alloying process was observed at a temperature higher than "alloying point". The mechanism of the high luminescence efficiency and stability of Zn(x)Cd(1-x)Se nanocrystals is explored.     

Syntheses, structures, and luminescent properties of dipyridylamine-functionalized anthracene and its complexes

A novel multidentate ligand with 2,2'-dipyridylamine functionalities, 1,8-bis[4-(2,2'-dipyridylamino)phenylacetylenyl]anthracene (1), has been synthesized through a double Sonogashira coupling reaction and characterized by NMR spectroscopic, elemental, and X-ray diffraction analyses. Compound 1 can bind to either one metal center as a tetradentate ligand or two metal centers as a double-bidentate ligand. In the double-bidentate mode, the distance between the two metal centers may vary significantly. Compound 1 displays bright blue luminescence in the solid state and in solution with a quantum efficiency of 64% relative to 9,10-diphenylanthracene. While the dirhodium complex of 1 shows no luminescence, the two zinc complexes of 1 display blue luminescence with quantum efficiencies slightly lower than that of 1. Organic light-emitting devices (OLEDs) using 1 as the emitter show a maximum current efficiency of 7 cd/A.     

Soluble rigid–flexible polyethers containing bis(biphenyl)anthracene or bis(styryl)anthracene units in the main chain for light-emitting applications

New rigid–flexible polyethers containing bis(biphenyl)anthracene or bis(styryl)anthracene units in the main chain were synthesized and characterized by viscosimetry, thermal and mechanical analysis, NMR, UV-vis, and luminescence spectroscopy. The polyethers containing bis(styryl)anthracene units in the main chain form free-standing films either from solution casting or after melt pressing at temperatures where they are thermally stable. The length of the flexible spacer influences the thermal and mechanical behavior of these polymers. The isotropization temperature as well as the glass transition temperature show an odd–even effect depending on the spacer segment length. Films with high modulus at room temperature and glass transition temperatures in the range 74–103°C were obtained using dynamic mechanical analysis. These polymers show bright-yellow photoluminescence with maximum at 580 nm in solution. In the solid state, the luminescence maximum is either red or blue shifted depending on the number of the methylene units in the aliphatic segment. The polyethers containing bis(biphenyl)anthracene units in the main chain are blue-light-emitting polymers with photoluminescence maxima at 435 and 455 nm in solution. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3826–3837, 1999     

Preparation, characterization and optical properties of lanthanum-(nanometer MCM-41) composite material

Nanometer MCM-41 molecular sieve was prepared under a base condition by using cetyltrimethylammonium bromide as template and tetraethyl orthosilicate as silica source by means of hydrothermal method. Lanthanum(III) was incorporated into the nanometer MCM-41 by a liquid phase grafting method. The prepared nanocomposite materials were characterized by means of powder X-ray diffraction, spectrophotometric anaylsis, Fourier transform infrared spectroscopy, low temperature nitrogen adsorption-desorption technique, solid diffuse reflectance absorption spectra and luminescence. The powder X-ray diffraction studies show that the nanometer MCM-41 molecular sieve is successfully prepared. The highly ordered mesoporous two-dimensional hexagonal channel structure and framework of the support MCM-41 is retained intact in the prepared composite material La-(nanometer MCM-41). The spectrophotometric anaylsis indicates that lanthanum exists in the prepared nanocomposite materials. The Fourier transform infrared spectra indicate that the framework of the MCM-41 molecular sieve still remains in the prepared nanocomposite materials and some framework vibration peaks show blue shifts relative to those of the MCM-41 molecular sieve. The low temperature nitrogen adsorption-desorption indicates that the guest locates in the channel of the molecular sieve. Compared with bulk lanthanum oxide, the guest in the channel of the molecular sieve has smaller particle size and shows a significant blue shift of optical absorption band in solid diffuse reflectance absorption spectra. The observed blue shift in the solid state diffuse reflectance absorption spectra of the lanthanum-(nanometer MCM-41) sample show the obvious stereoscopic confinement effect of the channel of the host on the guest, which further indicates the successful encapsulation of the guest in the host. The La-(nanometer MCM-41) sample shows luminescence.     

Blue-emitting dinuclear N-heterocyclic dicarbene gold(I) complex featuring a nearly unit quantum yield

Dinuclear N-heterocyclic dicarbene gold(I) complexes of general formula [Au(2)(RIm-Y-ImR)(2)](PF(6))(2) (R = Me, Cy; Y = (CH(2))(1-4), o-xylylene, m-xylylene) have been synthesized and screened for their luminescence properties. All the complexes are weakly emissive in solution whereas in the solid state some of them show significant luminescence intensities. In particular, crystals or powders of the complex with R = Me, Y = (CH(2))(3) exhibit an intense blue emission (λ(max) = 450 nm) with a high quantum yield (Φ(em) = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au···Au distance (3.272 ?). Time dependent density functional theory (TDDFT) calculations have been used to calculate the UV/vis properties of the ground state as well as of the first excited state of the complex, the latter featuring a significantly shorter Au···Au distance.     

Reversible luminescence thermochromism of dibenzoyl(methanato)boron difluoride

Reversible luminescence thermochromism of dibenzoyl(methanato)boron difluoride was found. A substantial hypsochromic shift of the luminescence band maximum (60 nm) with a temperature decrease from 300 to 77 K was observed, and the luminescence color changed from green to blue. A considerable decrease (by 0.386 Å) in the unit cell parameters along the c axis was detected by X-ray diffractometry when the temperature of the crystal decreased from 293 to 123 K. Shortening of the distances between the planes of adjacent molecules (stacking factor) weakens the interaction between the dimers and enhances the monomeric and excimeric luminescence. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1032–1034, April, 2005.     

Strong green emission from alpha-SiAlON activated by divalent ytterbium under blue light irradiation

This contribution reports on luminescence properties of divalent ytterbium in alpha-SiAlON at room temperature. Ytterbium-doped alpha-SiAlON powders, with the compositions of (M(1-2x/v)Yb(x))(m/v)Si(12-m-n)Al(m+n)O(n)N(16-n) (M = Ca, Li, Mg, and Y, v is the valency of M, 0.002 < or = x < or = 0.10, 0.5 < or = m = 2n < or = 3.5), were synthesized by sintering at 1700 degrees C for 2 h under 0.5 MPa N2. A single, intense, broad emission band, centered at 549 nm, is observed due to the electronic transitions from the excited state 4f(13)5d to the ground state 4f14 of Yb2+. The luminescence of Yb2+ in alpha-SiAlON occurs at relatively low energy, which is attributable to the large crystal field splitting and nephelauxetic effect due to the nitrogen-rich coordination of Yb2+. The dependence of luminescence properties on the Yb2+ concentration, chemical composition, and annealing is discussed. It is suggested that this novel green phosphor could be applied in white light-emitting diodes (LEDs) when combined with a red phosphor and a blue LED.     

Synthesis and characterization of new carbazole/fluorene‐based derivatives for blue‐light‐emitting devices

2,7‐Bis(9‐ethylcarbazol‐3‐yl)‐9,9‐di(2‐ethylhexyl)fluorene and a segmented copolymer composed of the same chromophores alternated with hexamethylene fragments were synthesized. The obtained materials possess good solubility in common organic solvents, high thermal stability with 1% weight loss temperature of 350–370 °C, and suitable glass transition temperatures. Both derivatives show blue fluorescence in dilute solutions as well as in solid state, demonstrating that excimers are not formed in the thin films. The fluorescence spectra of the materials do not show any peaks in the long‐wavelength region even after annealing at 200 °C in air. An organic LED with the configuration of ITO/copolymer/Al generates blue electroluminescence with the maximum peak at 416 nm, rather low turn‐on voltage (4.0 V), and brightness of about 400 cd/m². The heterostructure device based on model derivative emitted stable blue light with low operation voltage (100 cd/m² at ～11 V) and demonstrated luminescence efficiency of 0.8 cd/A. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5987–5994, 2006     

Time‐Dependent Afterglow Color in a Single‐Component Organic Molecular Crystal

An organic crystal of 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (pCBP) exhibits time‐dependent afterglow color from blue to orange over 1 s. Both experimental and computational data confirm that the color evolution results from well‐separated, long‐persistent thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) with different but comparable decay rates. TADF is enabled by a small S₁–T₁ energy gap of 0.7 kcal mol^?1. The good separation of TADF and RTP is due to a 11.8 kcal mol^?1 difference in the S₀ energies of the S₁ and T₁ structures, indicating that apart from the excited‐state properties, tuning the ground state is also important for luminescence properties. This afterglow color evolution of pCBP allows its applications in anticounterfeiting and data encryption with high security levels.     

Blue Luminescence of Dendrimer‐Encapsulated Gold Nanoclusters

Direct evidence for the blue luminescence of gold nanoclusters encapsulated inside hydroxyl‐terminated polyamidoamine (PAMAM) dendrimers was provided by spectroscopic studies as well as by theoretical calculations. Steady‐state and time‐resolved spectroscopic studies showed that the luminescence of the gold nanoclusters consisted largely of two electronic transitions. Theoretical calculations indicate that the two transitions are attributed to the different sizes of the gold nanoclusters (Au₈ and Au₁₃). The luminescence of the gold nanoclusters was clearly distinguished from that of the dendrimers.     

Reactivity of ZrO(MFP) and ZrO(RP) Nanoparticles with LnCl3 for Solvatochromic Luminescence Modification and pH-Dependent Optical Sensing

The luminescence of the inorganic–organic hybrid nanoparticles ZrO(MFP) (MFP=methylfluorescein phosphate) and ZrO(RP) (RP=resorufin phosphate) was modified by addition of different rare earth halides LnCl₃. The resulting composite materials form dispersible nanoparticles that exhibit modified nanoparticle fluorescence depending on the rare earth ion. The resulting chromaticity of the luminescence is further variable by the employment of different solvents for ZrO(MFP)-based composite systems. The strong solvatochromic effect of the MFP chromophore leads to different luminescence chromaticities of the composite materials between green, yellow, and blue in THF, toluene, and dichloromethane, respectively. The luminescence of ZrO(RP)-based composite particles can be modified between the red and blue spectral regions in dependence on the applied reaction temperature. Beside a luminescence shift that is derived from nanoparticle modification by LnCl₃, a strong turn-on effect of ZrO(RP) particles results after contact with different Brønsted acids and bases in combination with a respective chromaticity shift. Both effects enable the potential employment of such particles as highly sensitive optical pH sensors.     

Intense blue up-conversion luminescence in Tm3+/Yb3+ codoped oxyfluoride glass-ceramics containing beta-PbF2 nanocrystals

Up-conversion luminescence properties of a Tm3+/Yb3+ codoped oxyfluoride glass-ceramics under 980 nm excitation are investigated. Intense blue emission centered at 476 nm, corresponding to 1G4-->3H6 transitions of Tm3+ was simultaneously observed in the transparent oxyfluoride glass ceramics at room temperature. The intensity of the blue up-conversion luminescence in a 1 mol% YbF3-containing glass-ceramic was found to be about 40 times stronger than that in the precursor oxyfluoride glass. The reason for the intense Tm3+ up-conversion luminescence in the oxyfluoride glass-ceramics is discussed. The dependence of up-conversion intensities on excitation power and possible up-conversion mechanism are also evaluated.