Plasmon‐Enhanced Blue Upconversion Luminescence by Indium Nanocrystals

Numerous endeavors have been undertaken to gain enhanced upconversion luminescence via surface plasmon resonance (SPR) generated by specially designed nanostructures of noble metals (e.g., Au, Ag). However, the SPR response of these metals is usually weak in the ultraviolet (UV) region because of their intrinsic electronic configurations; thus, only green and red upconversion emissions can undergo significant plasmonic enhancement yet without selectivity, while an efficient approach to selectively enhancing the blue upconversion luminescence has been lacking. Herein, by integrating the pronounced UV SPR of silica‐coated indium nanocrystals (InNCs) with blue‐emission upconversion nanoparticles (UCNPs) of NaYbF₄:Tm, an up to tenfold selective luminescence enhancement at 450 nm is obtained upon 980 nm laser excitation. Precise manipulation of the silica shell thickness suggests an optimal working distance of 3 nm between InNCs and UCNPs. This study has, for the first time, realized selective blue upconversion luminescence enhancement by using an inexpensive, non‐noble metal material, which will not only enrich the fundamental investigations of SPR‐enhanced upconversion emission, but also widen the applications of blue light‐emitting nanomaterials, for example, in therapeutics.     

Ligand‐Driven Wavelength‐Tunable and Ultra‐Broadband Infrared Luminescence in Single‐Ion‐Doped Transparent Hybrid Materials

Here, tuning of the optical properties of emission centers by tailoring the ligand fields is investigated. Experimentally, it is demonstrated that Ni²⁺ can act as a single emission species in multiple octahedral local environments. Nanocrystal‐embedded hybrid materials are employed as hosts in order to take advantage of their convenience in local environment design for practical applications. Novel composite gain materials with high transparence are successfully made, and show interesting wavelength‐tunable and ultra‐broadband infrared luminescence covering the whole near‐infrared region from 1 100 to 1 800 nm. The infrared luminescence peak positions can be finely tuned from 1 300 to 1 450 and to 1 570 nm, with the largest full width at half maximum being about 400 nm and covering the telecommunication bands at 1 200–1 500 nm. According to the results of characterization, the unusual luminescence, interestingly, originates from Ni²⁺ in nanocrystals and the doping efficiency of Ni²⁺ is surprisingly high. The results demonstrate that the method presented may be an effective way to fabricate multifunctional light sources with various fundamental multifunctional applications from efficient broadband optical amplifiers to bio‐imaging.     

Upconversion Luminescent Chemodosimeter Based on NIR Organic Dye for Monitoring Methylmercury In Vivo

While most luminescent organic dyes display intense Stokes fluorescence, some of them exhibit unique single‐photon frequency upconversion luminescence (FUCL). Compared to conventional anti‐Stokes luminescence of lanthanides and two‐photon excitation, FUCL materials display adjustable spectrum area and require a much lower excitation power. Although this is very beneficial for biological applications in the perspective of reducing photodamage to biological samples and photobleaching of the dyes, the utilization of FUCL for biosensing and bioimaging in vivo has not been reported. In this study, we developed a near‐infrared (NIR) rhodamine derivative (FUC‐1) as a chemodosimeter, which displays weak luminescence but undergoes thiolactone ring‐open process leading to luminescence turn‐on in response to mercury(II) cation or methylmercury with good selectivity and high sensitivity in aqueous solution. Interestingly, FUC‐1 displays particular FUCL, excitation at 808 nm leads to luminescence at 745 nm. Compared to Stokes luminescence resulted from excitation at 630 nm, the use of FUCL lowers the detection limit of Hg²⁺ to be 0.207 nM. FUC‐1 has been used for FUCL bioimaging of methylmercury in live cells and mice. To the best of our knowledge, this is the first example of FUCL biosensing and bioimaging in vivo using visible and NIR fluorescence of small‐molecular dyes.     

The Active‐Core/Active‐Shell Approach: A Strategy to Enhance the Upconversion Luminescence in Lanthanide‐Doped Nanoparticles

Nanoparticles of NaGdF₄ doped with trivalent erbium (Er³⁺) and ytterbium (Yb³⁺) are prepared by a modified thermal decomposition synthesis from trifluoroacetate precursors in 1‐octadecene and oleic acid. The nanoparticles emit visible upconverted luminescence on excitation with near‐infrared light. To minimize quenching of this luminescence by surface defects and surface‐associated ligands, the nanoparticles are coated with a shell of NaGdF₄. The intensity of the upconversion luminescence is compared for nanoparticles that were coated with an undoped shell (inert shell) and similar particles coated with a Yb³⁺‐doped shell (active shell). Luminescence is also measured for nanoparticles lacking the shell (core only), and doped with Yb³⁺ at levels corresponding to the doped and undoped core/shell materials respectively. Upconversion luminescence was more intense for the core/shell materials than for the uncoated nanoparticles, and is greatest for the materials having the “active” doped shell. Increasing the Yb³⁺ concentration in the “core‐only” nanoparticles decreases the upconversion luminescence intensity. The processes responsible for the upconversion are presented and the potential advantages of “active‐core”/“active‐shell” nanoparticles are discussed.     

Defect engineering in implantation technology of silicon light-emitting structures with dislocation-related luminescence

Results obtained in development of physical foundations of ion implantation technology for fabrication of silicon light-emitting structures (LESs) based on dislocation-related luminescence and intended for operation at wavelengths close to ∼1.6 μm are summarized. The development of the concept of defect engineering in the technology of semiconductor devices makes it possible to determine the fundamental aspects of the process of defect formation; reveal specific features of the emission spectra related to changes in the implantation conditions of Er, Dy, Ho, O, and Si ions and the subsequent annealing; and design light-emitting structures with a desirable spectrum of luminescent centers and extended structural defects. The technological conditions in which only a single type of extended structural defect (Frank loops, perfect prismatic loops, or pure edge dislocations) is introduced into the light-emitting layer are found, which enables analysis of the correlation between the concentration of extended defects of a certain type and the intensity of lines of the dislocation-related luminescence. The key role of intrinsic point lattice defects in the origination and transformation of extended structural defects and luminescent centers responsible for the dislocation-related luminescence is revealed. It is found that the efficiency of luminescence excitation from the so-called D1 centers, which are of particular interest for practical applications, varies by more than two orders of magnitude between structures fabricated using different technological procedures. High-efficiency silicon light-emitting diodes with room-temperature dislocation-related luminescence have been fabricated.     

Composite Luminescent Material for Dual Sensing of Oxygen and Temperature

A novel kind of composite material is presented that contains two indicators incorporated into a single polymer matrix, thus allowing simultaneous determination of oxygen partial pressure and temperature. The temperature‐sensitive dye (ruthenium tris‐1,10‐phenanthroline) was chosen for its highly temperature‐dependent luminescence which is the highest among the Ru^II polypyridyl complexes. A fluorinated palladium(II) tetraphenylporphyrin served as the oxygen probe. The indicators were incorporated into either poly(styrene‐co‐acrylonitrile) microparticles (to sense oxygen) or into poly(acrylonitrile) (for temperature sensing, since this polymer is virtually impermeable to oxygen). The luminescence of both dyes can be separated either spectrally (due to different absorption and emission spectra of the indicators) or via luminescence decay time. The material is suitable for temperature‐compensated oxygen sensing, for example, in high‐resolution oxygen profiling, and for imaging temperature in the range between 0 and 60 °C. This enables one to “see” (rather than to “feel”) temperature in this important range. Simultaneous imaging of pressure and temperature also has been achieved. It enables contactless imaging of the two parameters, for example, in wind tunnels. Due to the use of a biocompatible hydrogel matrix, the material conceivably is suited for biomedical applications.     

X‐Ray‐Induced Persistent Luminescence Promotes Ultrasensitive Imaging and Effective Inhibition of Orthotopic Hepatic Tumors

Persistent luminescence imaging is accompanied by continuous illumination after the removal of excitation light, which can successfully prevent the generation of autofluorescence. In this study, a mesoporous silica template method is used to prepare uniform and monodisperse porous nanophosphors that can generate X‐ray‐excited persistent luminescence (XEPL). By loading photosensitizers, XEPL effectively excites the photosensitizers to produce reactive oxygen species for killing cancer cells. Imaging of orthotopic hepatic tumors in vivo shows that nanophosphors accumulate in the liver tumors through a passive targeting mechanism, as confirmed by the co‐imaging of bioluminescence and X‐ray‐excited luminescence. Under image‐guidance, X‐ray‐induced photodynamic therapy effectively inhibits the growth of orthotopic hepatic tumors with negligible side effects. Overall, X‐ray‐induced persistent luminescence promotes ultrasensitive imaging and effective inhibition of orthotopic hepatic tumors.     

Multistimuli‐Responsive Display Materials to Encrypt Differentiated Information in Bright and Dark Fields

Visually readable codes play a crucial role in anticounterfeiting measures. However, current coding approaches do not enable time‐dependent codes to be visually read, adjusted, and differentiated in bright and dark fields. Here, using a combined strategy of piezoelectric lattice selection, oxygen vacancy engineering, and activator doping, a lanthanide ion‐doped titanate is developed that integrates mechano‐, thermo‐, and photo‐responsive color change (>18 h for bright field), persistent luminescence (>6 h for dark field), and stimulus‐triggered multimodal luminescence. The feasibility of optical encoding, visual displaying, and stimulus‐responsive encrypting of time‐dependent, dual‐field information by using the developed material is demonstrated. In particular, the differentiated display of dual‐field modes is achieved by combining mechanostimulated abolition of only the persistent luminescence and thermo‐ and photostimulated reversal of both the color change and persistent luminescence. The results provide new insights for designing advanced materials and encryption technologies for photonic displays, information security, and intelligent anticounterfeiting.     

Vibration‐Induced Emission (VIE) of N,N′‐Disubstituted‐Dihydribenzo[a,c]phenazines: Fundamental Understanding and Emerging Applications

Organic fluorophores with dual‐emission and large Stokes shifts are attracting great attention due to their importance in fundamental research and technique applications. This Progress Report gives an account on how a novel luminescence mechanism termed vibration‐induced emission (VIE) is established. The VIE mechanism is coined for the rationalization of an alterable dual emission of V‐shaped N,N′‐disubstituded‐dihydribenzo[a,c]phenazines (DHPs), which are originated from a bent‐to‐planar vibration and the reverse in the excited state. The validation of the VIE mechanism is highlighted, such as the work reporting the utilization of chemically‐locked strategy to snapshot the excited‐state planarization of DHPs, and the application of the approach of steric hindrance‐induced planarization to tune the ground‐state geometry of DHPs. Moreover, the emerging applications of this VIE concept in photoelectric and biomedical disciplines are summarized. Additionally, further development of the VIE systems as well as the remaining challenges are prospected. This report could arouse wide interest from various fields to the specific area of VIE, which would not only broaden the VIE territory but also enlarge the scope of advanced functional materials.     

Low‐Dose X‐ray Activation of W(VI)‐Doped Persistent Luminescence Nanoparticles for Deep‐Tissue Photodynamic Therapy

Although photodynamic therapy (PDT) has served as an important strategy for treatment of various diseases, it still experiences many challenges, such as shallow penetration of light, high‐dose light irradiation, and low therapy efficiency in deep tissue. Here, a low‐dose X‐ray‐activated persistent luminescence nanoparticle (PLNP)‐mediated PDT nanoplatform for depth‐independent and repeatable cancer treatment has been reported. In order to improve therapeutic efficiency, this study first synthesizes W(VI)‐doped ZnGa₂O₄:Cr PLNPs with stronger persistent luminescence intensity and longer persistent luminescence time than traditional ZnGa₂O₄:Cr PLNPs. The proposed PLNPs can serve as a persistent excitation light source for PDT, even after X‐ray irradiation has been removed. Both in vitro and in vivo experiments demonstrate that low‐dose (0.18 Gy) X‐ray irradiation is sufficient to activate the PDT nanoplatform and causes significant inhibitory effect on tumor progression. Therefore, such PDT nanoplatform will provide a promising depth‐independent treatment mode for clinical cancer therapy in the future.     

Atomic‐Level Passivation of Individual Upconversion Nanocrystal for Single Particle Microscopic Imaging

Lanthanide‐doped upconversion nanoparticles (UCNPs) have significant applications for single‐molecule probes and high‐resolution display. However, one of their major hurdles is the weak luminescence, and this remains a grand challenge to achieve at the single‐particle level. Here, 484‐fold luminescence enhancement in LuF₃:Yb³⁺, Er³⁺ rhombic flake UCNPs is achieved, thanks to the Yb³⁺‐mediated local photothermal effect, and their original morphology, size, and good dispersibility are well preserved. These data show that the surface atomic structure of UCNPs as well as transfer from amorphous to ordered crystal structure is modulated by making use of the local photothermal conversion that is generated by the directional absorption of 980 nm light by Yb³⁺ ions. The confocal luminescence images obtained by super‐resolution stimulated emission depletion also show the great enhancement of individual LuF₃:Yb³⁺, Er³⁺ nanoparticles; the high signal‐to‐noise ratio images indicate that the laser treatment technology opens the door for single particle imaging and practical application.     

Efficient Nondoped Blue Fluorescent Organic Light‐Emitting Diodes (OLEDs) with a High External Quantum Efficiency of 9.4% @ 1000 cd m−2 Based on Phenanthroimidazole−Anthracene Derivative

Organic light‐emitting diodes (OLEDs) can promise flexible, light weight, energy conservation, and many other advantages for next‐generation display and lighting applications. However, achieving efficient blue electroluminescence still remains a challenge. Though both phosphorescent and thermally activated delayed fluorescence materials can realize high‐efficiency via effective triplet utilization, they need to be doped into appropriate host materials and often suffer from certain degree of efficiency roll‐off. Therefore, developing efficient blue‐emitting materials suitable for nondoped device with little efficiency roll‐off is of great significance in terms of practical applications. Herein, a phenanthroimidazole?anthracene blue‐emitting material is reported that can attain high efficiency at high luminescence in nondoped OLEDs. The maximum external quantum efficiency (EQE) of nondoped device is 9.44% which is acquired at the luminescence of 1000 cd m^?2. The EQE is still as high as 8.09% even the luminescence reaches 10 000 cd m^?2. The maximum luminescence is ≈57 000 cd m^?2. The electroluminescence (EL) spectrum shows an emission peak of 470 nm and the Commission International de L'Eclairage (CIE) coordinates is (0.14, 0.19) at the voltage of 7 V. To the best of the knowledge, this is among the best results of nondoped blue EL devices.     

A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

Correlating Emissive Non‐Geminate Charge Recombination with Photocurrent Generation Efficiency in Polymer/Perylene Diimide Organic Photovoltaic Blend Films

Evidence for a correlation between the dynamics of emissive non‐geminate charge recombination within organic photovoltaic (OPV) blend films and the photocurrent generation efficiency of the corresponding blend‐based solar cells is presented. Two model OPV systems that consist of binary blends of electron acceptor N′‐bis(1‐ethylpropyl)‐3,4,9,10‐perylene tetracarboxy diimide (PDI) with either poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) or poly(9,9‐dioctylindenofluorene‐co‐benzothiadiazole) (PIF8BT) as electron donor are studied. For the F8BT:PDI and PIF8BT:PDI devices photocurrent generation efficiency is shown to be related to the PDI crystallinity. In contrast to the F8BT:PDI system, thermal annealing of the PIF8BT:PDI layer at 90 °C has a positive impact on the photocurrent generation efficiency and yields a corresponding increase in PL quenching. The devices of both blends have a strongly reduced photocurrent on higher temperature annealing at 120 °C. Delayed luminescence spectroscopy suggests that the improved efficiency of photocurrent generation for the 90 °C annealed PIF8BT:PDI layer is a result of optimized transport of the photogenerated charge‐carriers as well as of enhanced PL quenching due to the maintenance of optimized polymer/PDI interfaces. The studies propose that charge transport in the blend films can be indirectly monitored from the recombination dynamics of free carriers that cause the delayed luminescence. For the F8BT:PDI and PIF8BT:PDI blend films these dynamics are best described by a power‐law decay function and are found to be temperature dependent.     

A mechanism of electroluminescence in silicon diodes with a high dislocation density

A new concept is suggested to explain the effect of dislocations on electroluminescence in silicon diodes. This concept is based on consideration of the spatial correlation between injected electrons and holes that recombine inside a dislocation core. This correlation leads to an increase in the probability of radiative recombination for electron-hole pairs. Two cases are analyzed. In the first case, the resulting current is controlled mainly by tunneling of electrons and holes along dislocations, which is followed by electron-hole recombination under the conditions of barrier lowering. In this situation, electroluminescence is not related to the fundamental absorption edge and the energy position of the electroluminescence band shifts to shorter wavelengths as either the temperature decreases or the applied voltage increases. In the second case, the diffusion-related component is prevalent in the total current. The radiative recombination of electron-hole pairs occurs in quasi-neutral regions and the electroluminescence exhibits an edge-related character. It is shown that the suggested mechanism may be responsible for a substantial enhancement of both the electroluminescence intensity and the quantum efficiency in silicon diodes with dislocations if the Shockley-Read-Hall lifetime is shorter than 10^?3 s.     

Diversity‐multiplexing tradeoff over correlated Rayleigh fading channels: a non‐asymptotic analysis

In this paper, we present a finite‐signal‐to‐noise ratio (finite‐SNR) framework to establish tight bounds on the diversity‐multiplexing tradeoff of a multiple input multiple output (MIMO) system. We focus on a more realistic propagation environment where MIMO channel fading coefficients are correlated and where SNR values are finite. The impact of spatial correlation on the fundamental diversity‐multiplexing tradeoff is investigated. We present tight lower bounds on the outage probability of both spatially uncorrelated and correlated MIMO channels. Using these lower bounds, accurate finite‐SNR estimates of the diversity‐multiplexing tradeoff are derived. These estimates allow to gain insight on the impact of spatial correlation on the diversity‐multiplexing tradeoff at finite‐SNR. As expected, the diversity‐multiplexing tradeoff is severely degraded as the spatial correlation increases. For example, a MIMO system operating at a spectral efficiency of R bps/Hz and at an SNR of 5 dB in a moderately correlated channel, achieves a better diversity gain than a system operating at the same spectral efficiency and at an SNR of 10 dB in a highly correlated channel, when the multiplexing gain r is greater than 0.8. Another interesting point is that provided that the spatial correlation channel matrix is of full rank, the maximum diversity gain is not affected by the spatial correlation. Copyright © 2009 John Wiley & Sons, Ltd.     

Differential method of analysis of luminescence spectra of semiconductors

A method for analyzing the luminescence spectra of semiconductors is suggested. The method is based on differentiation of the spectra. The potentialities of the method are demonstrated for luminescence in the region of the fundamental absorption edge of Si and SiGe alloy single crystals. The method is superior in accuracy to previously known luminescence methods of determining the band gap of indirect-gap semiconductors and practically insensitive to different conditions of outputting radiation from the sample.