长余辉发光粉Ba1-xCaxAl2O4:Eu2+, RE3+的发光特性及光谱分析

采用高温固相法制备了长余辉发光粉Ba1-xCaxAl2O4:Eu^2 ,RE^3 (RE^3 =Dy^3 ,Nd^3 ),测量了其发射光谱、激发光谱、余辉衰减光谱和热释光谱,分析了其发光特性。在紫外线的激发下样品的发射波长随着x的变化而变化,x从0到0．6的范围变化时,发射波长相应地从498nm减小到440nm,当x大于0．6以后,波长保持440nm不再变化。通过XRD光谱对其结构进行了分析,得出Ca离子在BaAl2O4基质中有极限溶解度x0=0．4,当x大于0．4时,基质结构中出现杂相。通过热释光谱,对基质中的陷阱情况进行了分析,解释了由于x值的不同而造成的余辉时间长短的差异。     

Simulation of H-centre migration along dislocation lines applied to UV-induced afterglow in Eu doped alkali halides

In this work we have simulated the migration of H centres along dislocation lines and their recombination with F z centres after a pulse irradiation. The variable parameter in our simulations was the probability p of recombination between H and F z centres when they meet. The results of the simulation for p =1 were in good agreement with a previous derived approximation and with the experimental data. We found that the function I = I 0 n m f could be fitted very well to the afterglow decay for all p values. The afterglow yield, defined as the total amount of afterglow, divided by the total amount of generated precursors of the H-F z pairs was found to decrease with increasing p . The exponent f however was found to be remarkably stable at 1.49 over a range of p from 1 to 0.2 below which it decreases to 0.5.     

Photo-Response with Radical Afterglow by Regulation of Spin Populations and Hole-Electron Distributions

No matter photoinduced organic radicals have been reported frequently, they are usually non-luminescent at ambient conditions. The internal mechanism on stability and electronic transitions of photoinduced radicals, is thus crucial for the development of relevant materials. Herein, a series of photoinduced radical emission systems were developed conveniently through doping benzoic acids into the hydrogen donor polyvinyl alcohol (PVA) matrix. Visual photoinduced radical emission and photochromism could be observed on Ph-3COOH @PVA film with the formation of cyclohexadienyl-type structure. For the first time, radical afterglow appeared with energy transfer from triplet state. The appropriate introduction of carboxylic groups to three nonadjacent carbon atoms on the benzene ring was the best for decreasing spin population and promoting electronic transitions of the radical. This study largely expands the radical emission property from both internal mechanism and practical application.     

Thermally Activated Long Persistent Luminescence of Organic Inorganic Metal Halides

Long persistent luminescence (LPL) materials of SrAl₂O₄ doped with Eu²⁺ or Dy³⁺ can maintain emission over hours after ceasing the excitation but suffer from insolubility, high cost, and harsh preparation. Recently, organic LPL of guest-host exciplex systems has been demonstrated via an intermediate charge-separated state with flexible design but poor air-stability. Here, we synthesized a nontoxic two-dimensional organic–inorganic metal hybrid halides (OIMHs), called PBA₂[ZnX₄] with X=Br or Cl and PBA=4-phenylbenzylamine. These materials exhibit stable LPL emission over minutes at room-temperature, which is two orders of magnitude longer than those of previously reported OIMHs. The mechanism study shows that the LPL emission comes from thermally activated charge separation state rather than room-temperature phosphorescence. Moreover, the LPL of PBA₂[ZnX₄] can be excited by low power sources, representing an effective strategy for developing low-cost and high-stability LPL systems.     

Purely Organic Fluorescence Afterglow: Visible-Light-Excitation,Inherent Mechanism,Tunable Color,and Practical Applications with Very Low Cost

Purely organic materials with visible light excitable fluorescence afterglow are promising for applications. Herein, fluorescence afterglow with various intensity and duration was observed on fluorescent dyes once being dispersed in polymer matrix, thanks to the slow reverse intersystem crossing rate (k_RISC) and long delayed fluorescence lifetime (τ_DF) derived from the coplanar and rigid chemical structure of the dyes. To verify the mechanism, different polymers were used to tune singlet-triplet splitting energy based on solvent effect. And commercial acriflavine (Acf) film showed blue shifted fluorescence compared to purified one, with slower k_RISC (≈10⁰ s⁻¹) and longer τ_DF (0.6 s). Via energy transfer from Acf to rhodamine B, the afterglow color was further regulated, with the largest fluorescence quantum yield of 42.4 %. It was demonstrated that the materials worked on color tunable light sources, and low-cost ($2 for 50 000 labels) anti-counterfeit labels recognized by white light.     

Functional Roles of Polymers in Room-Temperature Phosphorescent Materials: Modulation of Intersystem Crossing,Air Sensitivity and Biological Activity

Organic room-temperature phosphorescent (RTP) materials routinely incorporate polymeric components, which usually act as non-functional or “inert” media to protect excited-state phosphors from thermal and collisional quenching, but are lesser explored for other influences. Here, we report some exemplary “active roles” of polymer matrices played in organic RTP materials, including: 1) color modulation of total delayed emissions via balancing the population ratio between thermally-activated delayed fluorescence (TADF) and RTP due to dielectric-dependent intersystem crossing; 2) altered air sensitivity of RTP materials by generating various surface morphologies such as nano-sized granules; 3) enhanced bacterial elimination for enhanced electrostatic interactions with negatively charged bio-membranes. These active roles demonstrated that the vast library of polymeric structures and functionalities can be married to organic phosphors to broaden new application horizons for RTP materials.     

Amplification of noble gas ion lines in the afterglow of a pulsed hollow cathode discharge and possible benefit for analytical glow discharge mass spectrometry

A high-current pulsed hollow cathode discharge was used to study the role of atomic and ionic metastables involved in ionization plasma processes. We observed the enhancement of the spectral emission lines of noble gas ions in the afterglow. A study of the processes that involve atomic and ionic metastables is of great interest since it should lead to a better understanding of and enhanced control over the ionization mechanisms crucial to analytical glow discharge mass spectrometry (GDMS) analysis. Figure Time profile of Ti, Ti⁺, and Ne⁺ spectral lines     

Cr3+单掺杂及Eu3+/Cr3+共掺杂GdAlO3近红外长余辉发光纳米粒子的制备、微结构及光学特性

同时可作为磁共振成像造影剂与近红外余辉光学成像光学探针双功能的纳米粒子,在生物医学领域具有重要的应用价值。采用自蔓延燃烧法制备了不同掺杂浓度的GdAlO₃∶x%Cr3+及GdAlO₃∶1%Cr3+, y%Eu3+近红外长余辉发光纳米粒子。并采用X射线衍射、扫描电子显微镜、激发和发射光谱及发光动力学分析等技术手段,较系统地研究了其微结构及光学特性。实验结果表明,Cr3+取代了GdAlO₃中的Al3+的格位,单掺样品的平均粒子尺寸约为202 nm。GdAlO₃∶x%Cr3+样品的激发谱显示,激发峰来源于Cr3+和Gd3+的跃迁;在583 nm的激发下,在650～750 nm近红外范围内,出现四个近红外光发射峰。其中,725 nm处的发射峰归属为禁戒跃迁2E到4A₂的零声子线, 700和750 nm处的发射峰则为声子边带的发射。在0.2%～2.0%的掺杂浓度范围内,随着Cr3+掺杂浓度的增加,这些发射峰的强度先增强后减弱,最优浓度为1%。而位于735 nm处的发射峰强度随Cr3+浓度增大而增大,其归属于Cr3+-Cr3+对的发光。同时,单掺样品可观察到位于725 nm的长余辉发光,其中GdAlO₃∶1%Cr3+纳米粒子的余辉时间最长,并超过30 s。在上述Cr3+最优浓度（1%）基础上,通过Eu3+取代GdAlO₃基质中Gd3+的格位,实现了Eu3+/Cr3+共掺杂。实验发现,在266 nm激发下,在红光区域范围内可观察到以位于614 nm处的发射为主的一系列发射峰。尤其,由于存在Eu3+到Cr3+的能量传递,在近红外区出现了位于725 nm处Cr3+的近红外发射峰。当Eu3+浓度为13%时,与Cr3+单掺杂样品相比,其样品的平均粒子尺寸虽然减小到167 nm,但在275 nm紫外光照射5 min停止后,发现共掺样品在位于725 nm处Cr3+的余辉发光强度明显增强。通过比较分析单掺和共掺样品的吸收和发射光谱及发光动力学的结果,验证了由于Eu3+到Cr3+的持续能量传递可引起较显著地近红外余辉发光增强的结论。同时,该研究为设计新型的近红外长余辉发光纳米材料提供了新的思路。     

Improved photoluminescence and afterglow in CaTiO3:Pr with addition of nanosized SiO2

Enhancement of the ¹D₂-³H₄ red emission in CaTiO₃:Pr³⁺ with addition of nanosized SiO₂ fabricated by a solid state reaction method is reported. The dynamical processes for the improvement of red emission were systematically investigated using photoluminescence (PL) and PL excitation spectra, and diffused reflectance spectra as well as time decay patterns of PL and persistent afterglow. Higher efficiency of energy transfer from CaTiO₃ host to the activator Pr³⁺ due to the improvement of crystallinity by SiO₂ addition was discussed in comparison with that of the SiO₂ free sample. The enhancement of persistent afterglow after the cessation of excitation in SiO₂ added CaTiO₃:Pr³⁺ was also analyzed by theoretically fitted results.