非硅醇盐无机溶胶凝胶法合成蓝色发光材料Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+)

以水玻璃(Na2SiO3)为硅源,柠檬酸三铵为PH值调节剂,通过离子交换,采用溶胶凝胶法低温合成Sr2MgSi2O7Eu2+,Dy3+蓝色发光材料。采用DTA、XRD、荧光光谱等手段对材料进行分析和表征,结果表明:前驱体干凝胶煅烧到1010℃后开始有Sr2MgSi2O7相形成,到1100℃完全转变成高纯相Sr2MgSi2O7,其产物疏松,颗粒小,不需研磨或稍加研磨便得超细粉。它的激发光谱在250～450nm之间存在一个强度较高的激发带,发射峰位于467nm,余辉时间超8h。此外,对溶胶凝胶的形成机理等进行了讨论。     

Semitransparent Circularly Polarized Phosphorescent Organic Light-Emitting Diodes with External Quantum Efficiency over 30% and Dissymmetry Factor Close to 10−2

To concurrently realize large electroluminescence dissymmetry factor and high device efficiency remains a formidable challenge in the development of circularly polarized organic light-emitting diode (CP-OLED). In this work, by introducing a famous chiral resource of R-camphor, two green chiral iridium(III) isomers of Λ/Δ-Ir-(R-camphor) containing dual stereogenic centers at iridium and ancillary ligand, are efficiently synthesized. Benefiting from their high phosphorescence quantum yields (≈93%) and obvious circularly polarized photoluminescence property with dissymmetry factors (|g_PL|) in the 10⁻³ order of magnitude, the circularly polarized phosphorescent organic light-emitting diodes using these chiral emitters show excellent performances with the maximum external quantum efficiency (EQE_max) of 30.6%, low efficiency roll-off, and intense circularly polarized electroluminescence signal with dissymmetry factor (g_EL) in the 10⁻⁴ order of magnitude. By the novel device engineering with semitransparent cathode, the resulting g_EL values are significantly boosted by one order of magnitude, up to 7.70 × 10⁻³, which is the highest among the CP-OLEDs with chiral iridium complexes. Noteworthy, the semitransparent devices deliver a record-high EQE_max of 18.8% among the semitransparent OLEDs. The combination of novel chiral Ir(III) complexes and the semitransparent devices sheds light on the development of high performance CP-OLEDs with simultaneously high efficiency and large dissymmetry factor.     

All‐Organic,Temporally Pure White Afterglow in Amorphous Films Using Complementary Blue and Greenish‐Yellow Ultralong Room Temperature Phosphors

Organic molecules exhibiting afterglow emission (lifetime longer than 0.1 s) under ambient conditions have sparked tremendous attention in recent years as a sustainable energy source with potential applications in displays, lighting, and bioimaging. However, white afterglow organic materials with color purity during the entire period of delayed emission, after the cessation of excitation source, are yet to be achieved due to the different excited state lifetimes of its primary or complementary components. Herein, a remarkable, ambient “temporally pure white afterglow,” which lasts for over 7 s, by coorganizing complementary blue and greenish‐yellow organic room temperature phosphors with similar ultralong lifetimes and efficiency, in an amorphous polymer film is demonstrated. One of the most efficient blue afterglow room temperature phosphors is also reported, with an ultralong lifetime up to 2.26 s and maximum quantum efficiency of 36.8%, from purely organic triazatruxenes en route to the realization of this white afterglow. Further, broad and complementary absorption features of the coorganized phosphors in the visible region facilitates an excitation‐dependent dynamic color‐tuning of the afterglow from sky‐blue to greenish‐yellow.     

A revision of the luminance decay time estimation methods for photoluminescent products

We present a comparison between the methods used by two regulatory standards to estimate the luminance decay time for photoluminescent safety signs and safety way guidance systems (SWGS). One of these standards is the international ISO 16069. The other is the Spanish regulatory standard UNE 23035‐1. Both standards define the luminance decay time as the time for the luminance emitted by the photoluminescent sample to reach 0.3 mcd/m² after the excitation light over the sample is removed. Due to the fact that decay time can be really long, they propose methods to estimate it by extrapolation. The points suggested by each standard to adjust the luminance decay time curve are quite different and so are the results obtained with them. To compare both methods, four different photoluminescent safety signs were tested using the methods provided by these two regulatory standards. The samples were illuminated for 5 min with a xenon‐arc source of light; luminance measurements after illumination were made with a B‐510 LMT photometer, for an interval of time according to methods explained by the standards. The results were compared with real measurements of luminance decay time for each sample, allowing the luminance value to reach 0.3 mcd/m². Results obtained from the extrapolating methods provided by each standard showed that standard ISO 16069 was much more accurate than UNE 23035‐1, which showed important deviations from real decay time values. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Rare‐earth materials for use in the dark

Abstract— Recently, it was found that some materials doped with rare‐earth ions show bright and long‐lasting phosphorescence. They do not include radioactive elements and can be safely used as luminous paints for use in the dark. Some of them are better than the traditional zinc sulfide doped with copper (ZnS:Cu). The most important rare‐earth materials with long‐lasting phosphorescence are aluminates such as alkaline‐earth aluminates MAl₂O₄:Eu²⁺, Dy³⁺ (M = Sr, Ca) and garnets Y₃Ga₅O₁₂:Tb³⁺, Gd₃Ga₅O₁₂:Tb³⁺, Cd₃Al₂Ge₃O₁₂:Tb³⁺, Cd₃M₂Ge₃O₁₂:Pr³⁺ (M = Al, Ge), Y₃Al_5?xGa_xO₁₂:Ce³⁺ (x = 3, 3.5). Some oxides such as InBO₃:Tb³⁺, Ba₂SiO₄:Dy³⁺ also show long‐lasting phosphorescence properties. Other sulfide materials include ZnS:Eu, Ca_xSr_1?x S:Bi, Tm, Cu or Ca_xSr_1?xS:Eu. Alkaline‐earth aluminates MAl₂O₄:Eu²⁺ (M = Mg, Ca, Sr, Ba) codoped with RE³⁺ (RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized by using homogeneous precipitation method.     

Enhancing Ultralong Organic Phosphorescence by Effective π‐Type Halogen Bonding

Efficient ultralong organic phosphorescent materials have potential applications in some fields, such as bioimaging, anti‐counterfeiting, and sensors. Nevertheless, phosphorescence efficiencies of metal‐free organic materials are low due to weak spin–orbit coupling and vigorous nonradiative transitions under ambient conditions. Here a chemical strategy to improve phosphorescence efficiency with intermolecular π‐type halogen bonding construction via isomerism is presented. X‐ray single crystal analysis reveals that different halogen bonding is formed among p‐BrTCz, m‐BrTCz, and o‐BrTCz crystals. Phosphorescence efficiency of m‐BrTCz in solid can reach 13.0%, seven times of o‐BrTCz in solid owing to effective π‐type halogen bonding, which is further confirmed by theoretical calculations. However, ultralong phosphorescence lifetimes are little affected, 155, 120, and 156 ms for p‐BrTCz, m‐BrTCz, and o‐BrTCz in the solid state, respectively. Furthermore, a simple pattern for data encryption and decryption is first demonstrated under sunlight. This result will provide an approach for improving the phosphorescent efficiency of metal‐free organic phosphors with ultralong luminescence.     

Self‐Protective Room‐Temperature Phosphorescence of Fluorine and Nitrogen Codoped Carbon Dots

The unstable triplet excited state is a core problem when developing self‐protective room temperature phosphorescence (RTP) in carbon dots (CDs). Here, fluorine and nitrogen codoped carbon dots (FNCDs) with long‐lived triplet excited states, emitting pH‐stabilized blue fluorescence and pH‐responsive green self‐protective RTP, are reported for the first time. The self‐protective RTP of FNCDs arises from n–π * electron transitions for C? N/C?N bonds with a small energy gap between singlet and triplet states at room temperature. Moreover, the interdot/intradot hydrogen bonds and steric protection of C? F bonds reduce quenching of RTP by oxygen at room temperature. The RTP emission of FNCDs shows outstanding reversibility, while the blue fluorescence emission has good pH stability. Based on these FNCDs, a data encoding/reading strategy for advanced anticounterfeiting is proposed via time‐resolved luminescence imaging techniques, as well as steganography of complex patterns.     

Doping‐Free Organic Light‐Emitting Diodes with Very High Power Efficiency,Simple Device Structure,and Superior Spectral Performance

Today's state‐of‐the‐art phosphorescent organic light‐emitting diodes (PhOLEDs) must rely on the host‐guest doping technique to decrease triplet quenching and increase device efficiency. However, doping is a sophisticated device fabrication process. Here, a Pt(II)‐based complex with a near unity photoluminescence quantum yield and excellent electron transporting properties in the form of neat film is reported. Simplified doping‐free white PhOLED and yellow‐orange PhOLED based on this emitter achieve rather low operating voltages (2.2–2.4 V) and very high power efficiencies of approximately 80 lm W^?1 (yellow‐orange) and 50 lm W^?1 (white), respectively, without any light extraction enhancement. Furthermore, the efficient white device also exhibits high color stability. No color shift is observed during the entire operation of the device. Analysis of the device's operational mechanism has been postulated in terms of exciton and polaron formation and fate. It is found that using the efficient neat Pt(II)‐complex as a homogeneous emitting and electron transporting layer and an ambipolar blue emitter are determining factors for achieving such a high efficiency.     

Highly Efficient Room-Temperature Phosphorescence Based on Single-Benzene Structure Molecules and Photoactivated Luminescence with Afterglow

Recently, a remarkable advance has been made for metal-free room-temperature phosphorescence (RTP) crystals with high phosphorescence quantum yield. However, amorphous, especially heavy-atom-free, RTP materials still suffer from low quantum yield due to the transition-forbidden character of phosphorescence and the relatively poor suppression of nonradiative transition in amorphous materials. In this study, a series of single-benzene structure-based high intersystem crossing yield phosphor is obtained. After embedding into polyvinyl alcohol matrix, all these phosphor exhibits efficient phosphorescence emission (Ф_P, up to 44.0%). Besides, photo-switchable phosphorescence emission can be obtained by doping these molecules into a polymethyl methacrylate (PMMA) matrix. The phosphorescence can be gradually switched on by consuming the residual oxygen in the PMMA matrix under continuous UV light irradiation. Furthermore, the phosphorescence will be spontaneously switched off under ambient conditions. Taking advantage of the photoactivation character, this material has potential in information storage and anti-counterfeiting.     

Optoelectronic properties of new functionalized heteroleptic iridium complex

A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline(1-piq) and a functionalized β-diketone(G1),Ir(1-piq)2G1,was synthesized and characterized by 1H-NMR,mass spectrometry and elemental analysis.The larger conjugation of the replacement of acetylacetone(acac) by a functionalized β-diketonate ligand led to a significant decrease in the HOMO level toward vacuum level,while Ir(1-piq)2G1 and Ir(1-piq)2(acac) showed red phosphorescent emissions of about 620 nm in dichloromethane...