936 | Nanoscale Horiz., 2021, 6, 936–938 This journal is © The Royal Society of Chemistry 2021

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Horizons Community Board collection: opticaland photonic materials

Xiaolu Zhuo, *a Li Na Quan *b and Qingchen Dong *c

Materials Horizons and Nanoscale Hori-zons set up their Community Boardsseveral years ago, aiming to support earlycareer researchers so that they couldshare their experiences and ideas onscientific publishing. As future leaders

in their respective fields, the CommunityBoards also provide a channel for mem-bers to build relationships across theirresearch community and develop theirown editorial skills.

This collection continues a series ofpost-publication online article collec-tions, led by our Community Boardmembers across both Materials Horizonsand Nanoscale Horizons.

Working together and sharing theirunique areas of expertise, our Commu-nity Board members have recommendedseveral key topics where significant,rapid progress has been made in the last

2 years. They have selected top articlespublished in the Horizons journals toshowcase the most important advancesin each topic area.

Optical and photonicmaterials

Xiaolu Zhuo, Li Na Quan and QingchenDong present this Horizons CommunityBoard collection on materials anddevices for optics and photonics.

Nowadays, optical and photonic mate-rials are closely related to technologicalprogress and are responsible for the

a CIC biomaGUNE, Basque Research and Technology

Alliance (BRTA), 20014 Donostia–San Sebastian,

Spain. E-mail: xzhuo@cicbiomagune.esb Department of Chemistry, Virginia Tech, Blacksburg,

VA, USA. E-mail: linaquan@vt.educ MOE Key Laboratory of Advanced Display and

System Applications, School of Mechanical &

Electronic Engineering and Automation, Shanghai

University, Shanghai, 200072, China.

E-mail: qcdong@shu.edu.cn

Xiaolu Zhuo

Nanoscale Horizons CommunityBoard member Xiaolu Zhuoobtained her PhD in Physics in2017 under the supervision ofProf. Jianfang Wang at theChinese University of Hong Kongand then conducted her firstpostdoctoral research in thesame group for one year. She iscurrently a Juan de la Ciervapostdoctoral fellow in theBioNanoPlasmonics group, ledby Prof. Luis M. Liz-Marzan, atCIC biomaGUNE in Spain. Her

research interests focus on plasmonics, nanophotonics, and bio-nanotechnology.

Li Na Quan

Materials Horizons CommunityBoard member Li Na Quanearned her PhD in Chemistryfrom Ewha Womans Universityin Seoul, South Korea, where sheworked with Prof. Dong Ha Kim.During her PhD, she worked withProf. Edward Sargent at theUniversity of Toronto (2014–2016). After receiving her docto-rate in 2016, she continued workas a postdoctoral researcher atthe University of Toronto andthen at the University of Califor-

nia, Berkeley with Prof. Peidong Yang. She started her independentcareer as an Assistant Professor at the Chemistry Department,Virginia Tech in early 2021. Her research focuses on the optical andelectronic properties of emerging semiconductors, such as perovs-kites, for use in next-generation optoelectronic applications.

DOI: 10.1039/d1nh90046c

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growth of entire industries. Accordingly,various materials based on differentproperties have been widely used inoptoelectronic devices or used as low-loss dielectrics for a range of vital opticaland photonic components across theinfrared wavelength range. In this collec-tion, we have compiled a list of commu-nications and reviews about theapplications of optical and photonicmaterials in various fields, includingluminescence, detection, photovoltaics,photodynamic therapy, optical sensing,bioimaging etc. We hope that this collec-tion will bring new inspiration andthoughts to researchers in the field ofoptoelectronic technology.

Materials

Optical and photonic materials include awide range of materials that generate,harvest, control, and respond to lightand photons, covering materials of dif-ferent scales from molecules to nano-/micro- particles and structures. Thedesign and preparation methods of newmaterials, as well as understanding theirintrinsic properties, are the foundationof the development of functional opticaland photonic devices.

Regarding the design of new opticalmaterials, much attention has been paidto luminescent quantum dots (QDs),organic small molecules, and perovs-kites, due to their crucial roles in bioima-ging, sensing, theranostics, and light-emitting devices. This focus includesnovel synthesis and fabrication methods,

the improvement of luminescence prop-erties, and the discovery of new lumines-cence mechanisms. Shen et al. reportedthe synthesis of lead-free FA3Bi2Br9 per-ovskite QDs with a bright blue emissionat 437 nm with a high photolumines-cence quantum yield of 52% (DOI: 10.1039/C9NH00685K). Li et al. designedand synthesized a new type of smallmolecule that coupled rigidity and flex-ibility to simultaneously achieve goodphotoacoustic, near-infrared fluores-cence, photodynamic, and photothermalproperties, enabling multifunctionalimaging and therapy (DOI: 10.1039/D0NH00672F). Dunlap-Shohl et al.demonstrated the resonant infraredmatrix-assisted pulsed laser evaporationtechnique for the thin film deposition ofa lead-halide-based perovskite, enablingfacile optical measurements anddevice fabrication based on perovskitethin films (DOI: 10.1039/C9MH00366E).A fast and intense X-ray scintillationresponse was observed from thehalide perovskite MAPbBr3 at low tem-peratures, reaching exceptionally highlight yields of 4100 000 ph MeV�1 andsub-nanosecond decay times (Mykhaylyket al., DOI: 10.1039/C9MH00281B).Strongly anisotropic 2D excitonic reso-nances were reported by Maserati et al.in a bulk metallorganic chalcogenide[AgSePh]N lamellar framework (DOI: 10.1039/C9MH01917K). A detailed study ofthe charge and energy transfer processeswas conducted by Ledee et al. based ontheir newly developed synthesis of two-dimensional halide perovskites contain-ing 100% of a photoactive tetrazine

derivative as the organic spacer in thelayered perovskites (DOI: 10.1039/D0MH01904F). Chen et al. reported a newfluorophore with aggregation-inducedemission characteristics and explored anew photoactivatable mechanism ofphoto-induced crystallization with emiss-ion enhancement (DOI: 10.1039/D0MH01200A). Okada et al. demonstratedthe self-assembly of photochromic mole-cules into optical microresonator arraysthat display switchable whispering gallerymode resonant photoluminescence forrewritable optical memory (DOI: 10.1039/D0MH00566E). Moreover, a few review arti-cles summarized the recent development inpolydopamine fluorescent nanomaterials(Yang et al., DOI: 10.1039/C9MH01197H),lanthanide-doped nanoparticles (Marinet al., DOI: 10.1039/D0NH00627K), and cop-per indium sulfide QDs (Morselli et al.,DOI: 10.1039/D1NH00260K).

In addition, progress has been madeon exploring new optical phenomenafrom other nanoparticles/nanostructuresand realizing various lab-demo applica-tions. Yin et al. developed the synthesisof mid-infrared-responsive plasmonicnanonails for molecular detection basedon surface-enhanced infrared absorp-tion spectroscopy (DOI: 10.1039/D0NH00244E). Liu et al. demonstra-ted a dual-responsive photonic liquidusing Fe3O4@polyvinylpyrrolidone@poly(N-isopropyl acrylamide) nanoparticles,which allows for the independent mod-ulation of the color brightness and hue(DOI: 10.1039/D1MH00556A). Chu et al.combined the nanoscale self-assembly ofcellulose nanocrystals with microscalediffraction grating to achieve freestand-ing photonic paper with programmablestructural color and polarization rotation(DOI: 10.1039/C9MH01485C).

Devices

The inherent advantages of optical andphotonic materials endow optoelectronicdevices, including photodiodes (PDs)field-effect transistors (FETs) and light-emitting diodes (LEDs), with multipleadvantages, such as a strong lightresponse, high carrier mobility, andexcellent luminescence characteristics,Qingchen Dong

Nanoscale Horizons Community Board memberQingchen Dong obtained her PhD under the tutelage ofProf. Wai-Yeung Wong in 2012 at Hong Kong BaptistUniversity. She also worked at Caltech with Prof. H. B.Gray from 2010 to 2011. She joined Taiyuan Universityof Technology from 2012 to 2021 and she now works atShanghai University as a full-time Professor. Herresearch involves the design and synthesis of functionalorganic and metallo-organic compounds for applicationsin data storage, artificial synapses and neuromorphiccomputing, optoelectronics, etc.

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938 | Nanoscale Horiz., 2021, 6, 936–938 This journal is © The Royal Society of Chemistry 2021

making them match or even exceed thecorresponding performance of amorphoussilicon devices. In this context, manyresearchers have made tremendous effortsto advance the development of optoelectro-nic devices. Ultraviolet (UV) PDs are highlydesired due to their great significance inmany applications. Huang et al. (DOI: 10.1039/D0MH00250J) reported ternary copperhalide (CsCu2I3) nanowires for the firsttime, which were used as the light absorberto achieve polarization sensitive and flexibleUV photodetector with a photocurrent ani-sotropy ratio of 3.16. Ma et al. (DOI: 10.1039/D1MH00776A) successfully designedand fabricated visible-blind UV narrowbandphotomultiplication-type organic photode-tectors (OPDs) using TAPC:C60 with aweight ratio of 50 : 1 as the active layer,exhibiting a narrowband response with afull-width at half-maximum of approxi-mately 36 nm, an ultrahigh external quan-tum efficiency (EQE) of 1.08 � 106% and aremarkable specific detectivity of 1.28 �1014 Jones at 335 nm wavelength under�14 V bias. In addition, they integrated aflexible UV photomultiplication-type OPDwith a flexible OLED to fabricate a wearableUV monitor, which can visually detect theintensity of weak UV light. Light emittingfield-effect transistors (LEFETs) are anemerging class of multifunctional optoelec-tronic device. A color-saturated, high-efficiency red QD hybrid light-emittingfield-effect transistor (QD-HLET) with anEQE of 22.8% and a field-effect mobilityof 3.1 cm2 V�1 s�1 was demonstrated by thegroup of Cao (DOI: 10.1039/D0MH00951B).LED technologies, such as organic LEDs(OLEDs), metal halide perovskite LEDsand QD LEDs (QLEDs) have achievedremarkable progress. Thompson’s group(DOI: 10.1039/C9MH00195F) describeda series of phenanthro[9,10-d]triazoleand phenanthro[9,10-d]imidazole basedmaterials which serve as alternatives tocarbazoles for achieving high triplet ener-gies as hosts for blue phosphors in OLEDs.Similarly to phosphorescent organometallicemitters, purely organic thermally activateddelayed fluorescence (TADF) emitters canrecruit both singlet and triplet excitions for

light emission and hence achieve 100%internal quantum efficiencies (IQE).Recently, a Focus article on the excitonharvesting mechanism of TADF materialsfrom the same group (DOI: 10.1039/D0MH00276C) systematically introducedthe routes for efficient radiative decay fromS1 and T1 states and described the TADFprocess in depth. Costa et al. (DOI: 10.1039/D0MH00503G) presented a new family ofbio-hybrid light-emitting diodes (Bio-HLEDs) with silk fibroin as a packagingmatrix and fluorescent proteins as emitters.List-Kratochvil et al. (DOI: 10.1039/D0MH00512F) reported a perovskite LEDbased on inkjet-printed MAPbBr3 activelayer for the first time. QLED technologyhas emerged for next-generation smart dis-plays due to the demand for higher colorsaturation and higher electrical stability.The progress of QLED technology for next-generation displays is summarized by Kimet al. (DOI: 10.1039/D0NH00556H). Green-ham et al. (DOI: 10.1039/C8MH01122B)reported an efficient donor–acceptor QDsystem by embedding a relatively smallfraction of well-passivated acceptor QDs.Yang et al. (DOI: 10.1039/D0NH00606H)explored the solution-processed fabricationof tricolored white lighting QLEDs based onthe novel combination of three environ-mentally benign primary color emitters ofblue and green ZnSeTe and red Zn–Cu–In–S QDs.

Advanced methods andcharacterization

To understand the fundamental physicalscience in optical and photonic materi-als, using advanced methods and char-acterizations are a prerequisite to furtherdeveloping the materials for practicalapplications. Materials with periodic pat-terns of nano- to micro-scale pores havebeen used for photonic applications fordecades, however, the characterization ofthe pore size distribution, pore curvatureand specific surface area has been lim-ited by using electron microscopy andnitrogen absorption (BET) methods.

Welborn et al. employed small-angleX-ray scattering (SAXS) as a reciprocalspace characterization tool that can pro-vide statistically representative micro-structure information in a wide range ofmaterials (DOI: 10.1039/C9NH00347A).In organic light-emitting materials, thetriplet state is one of the major excitonloss channels involved in the degrada-tion of light-emitting devices. To studythe non-emissive triplet state, Gruneet al. developed transient opticallydetected magnetic resonance to detectthe paramagnetic spin states of the lumi-nescence organic materials. Such tripletexcitons in organic luminescence materi-als can also be converted to singlets onTADF materials and then transferred tothe fluorescent material by long-rangeForster energy transfer (DOI: 10.1039/D1MH00999K). Haase et al. employed var-ious optical spectroscopy tools to investi-gate Dexter energy transfer from the TADFtriplet state to the non-emissive triplet ofthe fluorescence light emitters, which is thekey loss mechanism in light-emittingdevices (DOI: 10.1039/D0MH01666G). Inexcitonic organic semiconductors, it isimportant to understand the nature of elec-tron and hole separations under photoexci-tation. To have a deeper understanding ofphotoinduced charge separation in donor/acceptor heterojunctions, Kang et al., uti-lized pump–probe ultrafast transientabsorption spectroscopy and time-resolvedmicrowave conductivity techniques. Theyfound that the rigid bonds and low reorga-nization energy, as well as the highly delo-calized charge carriers in single-walledcarbon nanotubes, limit the formation ofthe charge transfer state in heterojunctions(DOI: 10.1039/D0MH01810D). In the area ofdeveloping efficient light-emitting materi-als, the use of theoretical tools, such asmachine learning/artificial intelligence,can further support to predict the structureand property relationships etc. Parker et al.directly compared the supervised and unsu-pervised approaches and used artificialneural networks to determine the emittingwavelengths in fluorescent silicon QDs(DOI: 10.1039/D0NH00637H).

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