Amplified circularly polarized luminescence enabled by photon upconversion in spin-coating cellulose matrix

It is of great significance to construct organic circularly polarized luminescence systems(CPL) with large luminescence dissymmetry factors(g_(lum)) for practical applications. Here we report organic CPL systems constructed by merging triplet-triplet annihilation upconversion chromophores in cellulose matrices. The chirality of the matrix is transferred to the achiral chromophores of photon upconversion and then the multistep energy transfer processes of upconversion amplify g_(lum). The g_(lum)value of upconversion CPL in the left-handed ethyl cellulose and the right-handed(acetyl) ethyl cellulose are up to +0.1 and -0.15, respectively. The study provides a straightforward approach for constructing solid organic upconversion CPL materials with large g_(lum), which may expand the application potentials of organic chiroptical materials.

Photoswitchable Photon Upconversion from Turn-on Mode Fluorescent Diarylethenes

Photon upconversion(UC)is one kind of anti-Stokes shift process,which generally requires a combination of two or more low-energy photons to produce one high-energy photon.However,another interesting anti-Stokes process,namely,single-photon-absorption-based upconversion(SPA-UC),can take place by exciting thermally excited vibrational-rotational energy levels of ground state to the first level of excited state.This phenomenon is less involved in organic systems due to the limitation of appropriate materials.Herein,for the first time,we have demonstrated a series of turn-on mode fluorescent diarylethenes,including Thiophene-and p-alkoxybromo-substituted phenyl-substituted derivatives(DAES and DAEC4),which exhibited SPA-UC phenomenon in the closed-ring state.An anti-Stokes shift of 0.36 eV was observed in these molecules,which was the highest value accessible in such UC systems.A relatively high quantum efficiency(13.5%)was evaluated through a relative method by using methylene blue as a standard.Phonon-assisted or hot band absorption was in charge of the achievement of SPA-UC.Besides,the upconverted emission could be switched on/off by cyclization and cycloreversion reaction,regulated by UV–visible light.Thus,this unique finding of the SPA-UC phenomena in photoswitchable diarylethenes might enrich the development of new molecular engineering strategies for designing photofunctional materials.

Chiral self-assembly regulated photon upconversion based on triplet-triplet annihilation

Photon upconversion(UC)based on triplet-triplet annihilation(TTA)in quasi-solid or solid state has been attracting much research interest due to its great potential applications.To get effective UC,precisely controlled donor-acceptor interaction is vitally important.Chiral self-assembly provides a powerful approach for sophisticated regulation of molecular interaction.Here we report a chiral self-assembly controlled TTA-UC system composed of chiral acceptor and achiral donor.It is found that racemic mixture of acceptors could form straight fibrous nanostructures,which show strong UC emission,while chiral assemblies for homochiral acceptors emit weak upconverted light.The racemic assemblies allow efficient triplet-triplet energy transfer(TTET)and further realize efficient UC emission,while the homochiral assemblies from chiral acceptor produce twisted nanostructures,suppressing efficient triplet energy transfer and annihilation.The establishment of such chiral self-assembly controlled UC system highlights the potential applications of triplet fusion in optoelectronic materials and provides a new perspective for designing highly effective UC systems.

Large-energy-shift photon upconversion in degenerately doped InP nanowires by direct excitation into the electron gas

Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.

Triplet−Triplet Annihilation-Based Photon Upconversion with a Macrocyclic Parallel Dimer

The integration of multiple chromophore units into a single molecule is expected to improve the performance of photon upconversion based on triplet−triplet annihilation(TTA-UC)that can convert low energy photons to higher energy photons at low excitation intensity.In this study,a macrocyclic parallel dimer of 9,10-diphenylanthracene(DPA)with a precisely parallel orientation,named MPD-2,is synthesized,and its TTAUC properties are investigated.MPD-2 shows a green-to-blue TTA-UC emission in the presence of a triplet sensitizer,platinum octaethylporphyrin(PtOEP).Compared to monomeric DPA,MPD-2 results in an enhancement of the spin statistical factor of TTA and a decrease in the excitation light intensity due to the intramolecular TTA process.The obtained structure−property relationship provides important information for the further improvement of TTA-UC properties.

Triplet-triplet annihilation upconversion materials as electrophoretic inks

Luminescent materials that can be reversibly switched by electric field stimulation are attractive since the potential application for optoelectronic devices.Here we report a triplet-triplet annihilation upconversion(TTA-UC)system with electrophoretic response which is developed as the electrophoretic ink.The TTA-UC system consists of an ionic derivative of 9,10-diphenyl anthracene(DPA)as the annihilator and Pt(II)octaethylporphyrin(PtOEP)as the sensitizer.Upon applying an electric field,migration and enrichment of positively charged DPA derivatives towards the cathode results in a 20%enhancement of TTA-UC.A quasi-solid film for electrically writing is made using the electrophoretic TTA system as the ink and a platinum electrode as a pen.The prototype of TTA-UC ink demonstrates unique luminescence functions upon electrically writing and erasing,providing a promising strategy to develop electronic devices for display,information storage and encryption.

Regulated polarization degree of upconversion luminescence and multiple anti-counterfeit applications

Polarization upconversion luminescence(PUCL)of lanthanide ions(Ln^(3+))has been widely used in single particle tracking,microfluidics detection,three-dimensional displays,and so on.However,no effective strategy has been developed for modulating PUCL.Here we report a strategy to regulate PUCL in Ho^(3+)-doped NaYF4single nanorods based on the number of upconversion photons.By constructing a multiphoton upconversion system for Ho^(3+),we regulate the degree of polarization(DOP)of PUCL from 0.590 for two-photon luminescence to 0.929 for three-photon upconversion luminescence(UCL).Furthermore,our strategy is verified from cross-relaxation between Ho^(3+)and Yb^(3+),excitation wavelength,excitation power density,and local site symmetry.And this regulation strategy of PUCL has also been achieved in Tm^(3+),with the DOP ranging from 0.233 for two-photon luminescence to 0.925 for four-photon UCL Besides,multi-dimensional anti-counterfeiting display has been explored with PUCL.This work provides an effective strategy for regulating PUCL and also provides more opportunities for the development of polarization display optical encoding,anti-counterfeiting,and integrated optical devices.

Controlling upconversion through interfacial energy transfer(IET):Fundamentals and applications

Photon upconversion has received substantial attention owing to its great promise in broad applications from bioimaging to other frontier fields like display,upconversion laser,information security and anticounterfeiting.A smart control and manipulation of the upconversion luminescence has always been a key topic,however,to date the most efficient mechanism for upconversion nanoparticles remains the energy transfer upconversion and recently reported energy migration mediated upconversion.Recently,we found that the interfacial energy transfer(IET)is also an efficient approach for enabling and tuning photon upconversion of lanthanide ions.Moreover,it can be used for the mechanistic understanding of the interionic interactions such as energy transfer and energy migration on the nanoscale.In this review,the recent advances of the research on the IET are summarized,the principles for designing IET process and typical examples are discussed together with its applications in both mechanistic research and frontier information security.The challenges and perspectives for future research are also commented.

Preparation and upconversion luminescence modification of YbPO4:Er3+inverse opal heterostructure

Photonic crystal heterostructures composed of YbPO4：Er^（3＋） inverse opal and polystyrene opal were prepared via a template-assisted process, which exhibited two photonic band gaps. The microstructure,phase and optical properties of photonic crystal heterostructures were investigated by x-ray diffraction,scanning electron microscopy, fluorescence spectroscopy, absorption spectroscopy, fluorescence lifetime,etc. The upconversion emission suppression caused by single photonic band gap from the following YbPO4：Er^（3＋） inverse opal or the upper opal was observed. The upconversion luminescence was strongly suppressed due to the two photonic band gap overlapping effect caused by the following YbPO4：Er^（3＋） inverse opal or the upper opal. The modified mechanisms of upconversion luminescence were discussed by the upconversion luminescence lifetime of YbPO4：Er^（3＋） photonic crystal heterostructures. The results demonstrated the modified upconversion luminescence is attributed to the photon trapping caused by Bragg reflection of photonic crystal heterostructures.

Let the light be a guide:Chromophore communication in metalorganic frameworks

The photonic characteristics of chromophore-containing metal-organic frameworks(MOFs)have led to extensive photophysical studies in an effort to capitalize on the potency of precisely controlled chromophore ensembles.Several examples have laid the foundation that demonstrates how photophysical properties of chromophores can be manipulated by tuning their communications(interactions)through integration within a MOF matrix.The main focus of this review is on harnessing the versatile MOF platform to accentuate the photophysical properties of integrated chromophores.In particular,this review will highlight chromophore dynamics that enhance,alter,or tune the photoluminescence response of single-and multi-chromophore-containing scaffolds,as well as alignment-guided anisotropic fluorescence.Building upon this groundwork,utilization of a hybrid crystalline motif can induce preferential orientation of chromophores resulting in enhanced communication and tailored behavior compared to randomly oriented emissive molecules.Moreover,frameworks that produce upconverted emission via sensitized triplet-triplet annihilation(sTTA),excited-state absorption(ESA),energy transfer upconversion(ETU),multi-photon absorption(MPA),or second-harmonic generation(SHG)can invoke dynamic control of material properties using photochromic linkers and will be discussed herein with a focus on the effects of chromophore alignment.Integration within a framework is a vehicle tofuse chromophores into solid-state platforms,opening an avenue for chromophore utilization in applications such as portable electronics that require solids or thin films.For those reasons,the design of chromophore-containing MOFs with desirable properties that rely on the alignment and communication of hundreds of chromophores within a single platform is a pressing demand for the development of futuristic technologies.