Symposium FK
Exploring Cutting-Edge Innovations in Luminescent Materials and Technologies for Display, Lighting and Emerging Photonic Applications
ABSTRACTS
Session FK-1 Material design and processing
FK-1:IL01 Intermolecular Charge Transfer Approach for TADF Emitters
KEN-TSUNG WONG, Department of Chemistry, National Taiwan University, Taipei, Taiwan
Upon photoexcitation of a donor (D): acceptor (A) blend, an exciplex system can be feasibly generated by intermolecular charge transfer. The exciplex-forming systems that can perform thermally activated delayed fluorescence (TADF) characteristics are emerging as appealing research targets due to their versatile applications in organic light-emitting devices (OLEDs). However, the polaron formation by the dissociation of exciplex exciton can largely affect the radiative relaxation process, leading to inferior photoluminescence quantum yield of an exciplex-forming blend as compared to that of molecular TADF materials. To understand the detailed D-A interactions is crucial for the study of the exciplex-forming mechanism and the deep insight understanding of exciplex excited state. This demand motivated us to establish exciplex-enabling supramolecular systems comprising tailor-made hosts with a variety of chemical structures and guests that can eventually lead to the formation of exciplex emission. The X-ray structure analyses of these supramolecular complexes reveal the donor-acceptor molecular interactions. In this conference, the photophysical properties of various supramolecular donor-acceptor systems that can be verified with the TADF exciplex characters will be reported.
FK-1:IL02 Polymer Photonic Crystal to Control Light Emission
D. COMORETTO, Dipartimento di Chimica e Chimica Industriale, Università di Genova, Genova, Italy
Polymers and their nanostructures represent an interesting alternative to traditional metal oxides for photonic applications as they are easy to process and enable lightweight, free-standing and flexible structures. Polymer distributed Bragg reflectors allow the development of label-free environment or food quality sensors, which are essential for reducing food waste.[1,2] NIR tuned multilayered photonic aegises allow to reduce heating from sunlight emission.[3] In the meantime, strongly scattering lossless systems made by recycled polymers allow to achieve sub-ambient radiative cooling. Both these approaches enable passive control of temperature thus providing a boost to building energy sustainability. Moreover, thermoplastic elastomers can be used to prepare mechanochromic photonic crystals, which can be used either to monitor mechanical stresses or to modulate the optical properties of materials.[4] Finally, polymer microcavities and metamaterials allow to engineer both the fluorescence radiative rate and spectral redistribution, which joined to strong-coupling are at the cornerstone of modern photonics and quantum technologies.[5,6] Special emphasis will be given to the use of recycled polymers or sulphur waste to built-up such nanostructures [7,8].
[1] L. Magnasco et al., Fluorimetric Detection of Vapor Pollutants with Diketopyrrolopyrrole Polymer Microcavities, ACS Omega 9, 42375 – 42385 (2024). [2] L. Magnasco et al., Polymer planar microcavities with CdSe-ZnS core-shell quantum dots for label-free vapor sensing, Responsive Mater. 3, e70017 (2025). [3] A. Lanfranchi et al., Engineering all-polymer planar photonic crystals as aegises against sunlight overheating, Chem. Eng. Sci. 2835, 119377 (2024). [4] M. Martusciello et al., Stretchable Distributed Bragg Reflectors as Strain-Responsive Mechanochromic Sensors, ACS Appl. Mat. Int. 16, 51384 – 51396 (2024). [5] H. Meghad et al., Control of near-infrared dye fluorescence lifetime in all-polymer microcavities, Mat. Chem. Front. 6, 2413 – 2421 (2022). [6] M. Martusciello et al., Dip Coating Fabrication Of All-Polymer Multilayer Photonic Crystals Through 3D Printer Conversion, ACS Appl. Polym. Mater. 7, 4779-4786 (2025). [7] A. Escher et al., From Landfill to Photonics: The Upcycling of Plastic Waste, ACS Appl. Polym. Mater. 6, 6917-6925 (2024). [8] C. Tavella et al., 2,5-Diisopropenylthiophene by Suzuki-Miyaura cross-coupling reaction and its exploitation in inverse vulcanization: a case study, RSC Advances 12, 8924-8935 (2022).
FK-1:L03b Frontiers of Organic Emissive Materials: OLEDs and Organic Semiconductor Laser Materials
C. ADACHI, Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, Fukuoka, Japan
Organic luminescent materials have achieved remarkable progress as key components in organic light-emitting diodes (OLEDs) for advanced display technologies. In particular, the invention of thermally activated delayed fluorescence (TADF)1 has enabled highly efficient electroluminescence by harvesting triplet excitons in purely organic aromatic compounds, thereby achieving practical performance. Recently, multi-resonance (MR)-type TADF emitters have attracted significant attention due to their ability to achieve deep-blue emission with extremely high color purity. In addition, enhancing the radiative decay rate has become a crucial strategy for realizing high brightness and long operational lifetimes. Furthermore, emerging concepts such as hyperfluorescence (HF) and phosphorescence-sensitized fluorescence (PSF) are expanding the design space for high-performance OLEDs. On the other hand, organic semiconductor lasers (OSLs)2, which are promising candidates for next-generation coherent light sources, require breakthroughs in molecular design and photophysics. Key challenges include reducing the lasing threshold, increasing optical gain, suppressing triplet absorption, and overcoming aggregation-induced quenching. In this talk, recent molecular design strategies will be presented, including the simultaneous optimization of the singlet–triplet energy gap (ΔEST) and radiative decay rate, rigid molecular frameworks, and host–guest engineering. The extension of design principles established in OLED research toward OSL development will be discussed. Further, the prospects and remaining challenges toward the realization of electrically driven organic lasers will be addressed.
[1] T. Uoyama et al., Nature, 492, 234 (2012); [2] C. Adachi and A. S. D. Sandanayaka, CCS Chemistry, 2, 1203 (2020).
FK-1:IL04 Medium Effects (Polarity, Viscosity, Temperature) on the Luminescence Properties of Organic Dyes: From Lighting to Sensing Applications
B. BARDI, F. BERTOCCHI, L. VISIERI, L. BALDINI, C. SISSA, A. LAPINI, A. PAINELLI, F. TERENZIANI, Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
Organic dyes are exploited for many different applications, ranging from optoelectronics to (bio)imaging and sensing. The most responsive dyes are highly polarizable molecules, whose properties are strongly affected by the medium properties. In this contribution, we will focus on the medium effects on the luminescence properties of organic fluorophores, presenting experimental data and theoretical models for a deep understanding of the related mechanisms. Different types of media will be discussed, from solutions to polymers and solid-state matrices, and the different solvation regimes (fast electronic solvation vs slow “orientational” solvation) will be described and modeled to reproduce and rationalize experimental data. Intermolecular interactions (leading to fluorescence resonance energy transfer – FRET, excimer formation, aggregation) will be discussed as well, as handles to fine-tuning the properties of dense samples. The implications on different application fields will be reviewed, such as the matrix effect on optoelectronic devices (OLEDs and photovoltaic cells), viscosity sensing, and temperature sensing in solution and in biological samples.
FK-1:L07 Temperature-dependent Dielectric Permittivity and Ferroelectricity in Strained SrTiO3
SOHM APTE, A.A. DEMKOV, Department of Physics, The University of Texas at Austin, Austin, TX, USA
We investigate the dielectric response as a function of temperature and applied strain of the prototypical perovskite SrTiO3 using ab initio molecular dynamics to calculate the complex, dynamical, temperature-dependent lattice dielectric function. The results show excellent agreement with experiment. On the application of tensile uniaxial strain, the static susceptibility shows divergence indicative of a ferroelectric transition. We calculate the required critical strain (3.8 %) and estimate the critical exponents of the second-order phase transition. We also see emergence of the antiferrodistortive (AFD) phase transition at ≈110 K. The method can be readily applied to study the dielectric properties and phase transitions in other ferroelectric materials at finite temperatures.
FK-1:L08 Nanoparticles, Quantum Dots, and Nanocrystals: Synthesis, Properties, and Applications
N.D. ZHUKOV1,2, V.V. BELYAEV3,4, A.A. PASYNKOV3, A.A. BELYAEV3, JIE SUN5,6,7,8, QUN YAN5,6, 1Limited Liability Company NPP Volga, Saratov; 2Institute of Physics, Saratov State University, Saratov, Russia; 3State University of Education, Moscow, Russia; 4RUDN University (Peoples’ Friendship University of Russia), Moscow, Russia; 5College of Physics and Information Engineering, Fuzhou University, China; 6Fujian Science and Technology Innovation Laboratory for Optoelectronic Information of China, Fuzhou, China; 7Department of Microscience and Nanotechnology, Fuzhou University, China; 8Chalmers University of Technology, Gothenburg, Sweden
Analysis of colloidal semiconductor nanomaterials is presented with precise classification framework based on structural perfection and quantum confine-ment effects. Nanocrystals (NC) require specific morphological control and crys-tallographic integrity to exhibit advanced quantum phenomena including quan-tized conductance, single-electron charging, and quantum entanglement. We de-velop detailed thermodynamic model of nucleation processes, calculate maxi-mum size for defect-free NC of some semiconductors: CdSe (~17nm), PbS (~16nm), HgSe (~10nm), and InSb (~6nm). Electronic transport in quantum-confined structures is rigorously described using finite potential well approxima-tion, with derived analytical expressions for electron transmission probability and resonant quantum conductance conditions. The research further investigates quantum oscillations and Bloch phenomena in confined systems, providing fun-damental insights into nanoscale charge transport mechanisms. The theoretical framework enables precise prediction of quantum effects in nanostructured mate-rials, highlighting NC unique potential to develop advanced quantum computing elements, integrated photonic circuits, next-generation information processing systems beyond conventional semiconductor technologies.
Session FK-2 Processes for optoelectronic and photonic applications
FK-2:IL09 Sub-5-micron InGaN-based Micro-LEDs Formed with Neutral Beam Etching
XUELUN WANG, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan; D. OHORI, Tohoku University, Sendai, Japan; S. SAMUKAWA, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
High-efficiency sub-5-micron InGaN micro-LEDs are highly required for VR/AR microdisplays. However, the fabrication of high-efficiency sub-5-micron InGaN micro-LEDs is a significant technical challenge owing to the existence of strong sidewall nonradiative recombination induced by plasma etching. We employed an ultralow damage dry etching technique, i.e., neutral beam etching (NBE), to fabricate GaN micro-LEDs. In this technique, a carbon plate with high-aspect-ratio apertures is placed between the plasma and etching chamber. Ions are neutralized when passing through the apertures, resulting in the formation of a beam of neutral particles for etching. The NBE technique can realize ultralow damage etching of various semiconductor materials owing to the complete suppression of the ion bombardment effect. We have demonstrated 3.5 x 3.5 μm2 GaN blue micro-LEDs with negligible sidewall nonradiative recombination by using the NBE technique [1]. We further extended this technique to the fabrication of sub-micron InGaN micro-LEDs. In this talk, I will present recent progress on the fabrication of sub-5-micron InGaN micro-LEDs, including the demonstration of an InGaN micro-LED with a diameter as small as 200 nm.
[1] X. L. Wang, et al., Nat. Commun. 14 (2023) 7569.
FK-2:IL10 Cross-sensitivity and Bias in Luminescence Sensing: From Foes to Friends
N. PANOV1, LIYAN MING1, E. ANDREATO1, J. LIFANTE1, L. ALDAZ-CABALLERO1, A. ROMELLI2, G. LIFANTE-PEDROLA1, A. BENAYAS1, P. CANTON2, D. JAQUE1, E. XIMENDES1, R. MARIN1,2, 1Nanomaterials for Bioimaging Group (nanoBIG), Dpto Física de Materiales, Universidad Autónoma de Madrid, Spain; 2Intelligent Optical Nanomaterials (IONs) group, Dpt Molecular Sciences & Nanosystems, Università Ca’ Foscari di Venezia, Italy
Luminescence sensing continues to attract the attention of several scientific communities, including materials scientists, optical spectroscopists, biologists, environmental scientists, and signal processing experts. The development of a luminescence sensing approach entails the design and preparation of the sensor, followed by its calibration and analysis of the luminescence signal. Properly performed, this process yields an approach capable of providing reliable and precise readouts of a parameter of interest. Yet, there are two major obstacles in this process: cross-sensitivity and bias. But are these phenomena really so disruptive to luminescence sensing? Can they be somehow harnessed? In this talk, we will touch upon our latest research achievements and challenges we encountered in the development of luminescence sensing approaches, focusing on temperature and pressure sensing as case studies. Novel nanoparticles and staple luminescent materials will be discussed in the context of luminescence sensing, introducing the concepts of cross-sensitivity and bias. This discussion will segue into a somewhat unexpected eulogy of these phenomena, which set the stage for augmenting the functionalities of luminescence sensing approaches.
FK-2:IL11 Identifying Rare Earth-Related Complexes that Enable Next Generation Display and Quantum Information Applications
B. MITCHELL, Department of Physics and Engineering, West Chester University, West Chester, PA, USA; MASAYOSHI TONOUCHI, Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan; V. DIEROLF, Department of Physics, Lehigh University, Bethlehem, PA, USA; YASUFUMI FUJIWARA, Research Organization of Science and Technology Ritsumeikan University, Kusatsu, Shiga, Japan
Next-generation optoelectronics—including solid-state lighting and quantum information systems—demand precise control over electroluminescence and spin–photon interfaces. These capabilities rely on understanding and engineering the defect complexes that form when rare-earth (RE) ions are introduced into semiconductor hosts. RE ions retain atomic-like optical and spin properties, but their efficiency depends critically on the nature of the local defect complexes they form and how those complexes mediate energy and spin transfer between the host and the RE ion. Identifying and controlling these RE–defect combinations—specific to both the dopant and the host—is now a central challenge for the field. In materials such as Eu-doped GaN, for instance, coupling between carrier-active defects and RE ions enables rapid, efficient excitation that produces sharp, stable optical transitions ideal for micro-LEDs and quantum emitters. Probing the carrier dynamics and complex formation mechanisms through high-frequency resolution photoluminescence, terahertz emission, and ultrafast spectroscopy offers a pathway to design RE-doped semiconductors with optimized defect chemistry for scalable optoelectronic and quantum technologies.
FK-2:IL12 Miniaturization of Perovskite and Organic Light-Emitting Diodes
CHIH-JEN SHIH, ETH Zurich, Zürich, Switzerland
Miniaturization of light-emitting diodes (LEDs) based on the emerging semiconductor materials, including perovskite and organic semiconductors, enables new technological opportunities beyond AR/VR displays. Patterning of the emissive semiconductor films represents the most critical step towards LED miniaturization. However, perovskite and organic semiconductors are not compatible with the solvent-intensive photolithography, while other patterning techniques such as inkjet and transfer printing may compromise scalability and/or achievable lateral resolution. Here I present our recent progress on nanopatterning of organic and perovskite semiconductors using nanostencil and molecular-beam holographic lithography (NSL and MBHL). The new techniques allow us to scalably fabricate nanopatterned perovskite and organic emitters with critical dimensions down to 100 nanometers. Accordingly, we demonstrated miniaturized LED pixels with the highest array densities up to 100,000 (single-color) and 10,000 (RGB) ppi, with external quantum efficiencies (EQEs) greater than 10%.
FK-2:IL13 Photons at Resonance for Biointegrated Optical Sensing and Manipulation
M.C. GATHER, University of Cologne, Cologne, Germany & University of St Andrews, Scotland
Joining the rich photo-physics of organic materials with the exquisite sensitivity of optical resonances to geometry and refractive index enables a plethora of devices with unusual and exciting properties. Examples from my team include flat microcavity sensors for interference-based detection of the mechanical forces exerted by cells, microlasers for real time sensing of cellular activity and long-term cell tracking, as well as the development of implants with extreme form factors that support optical stimulation of thousands of neurons deep in the brain with unprecedented spatial control. Very recently, by driving the interaction between excited states in organic materials and resonances in thin optical cavities into the strong coupling regime, we unlocked new tuning parameters which may enable a new generation of thin film optical filters with angle-independent characteristics as is required for more compact fluorescence-based sensing devices.
Session FK-3 Characterization of electro-optical-structural properties
FK-3:IL14 Time-resolved Photoemission Spectroscopy for Evaluation of Surface Carrier Recombination in Semiconductors
SHUHEI ICHIKAWA1,2, K. KOJIMA1, 1Graduate School of Engineering, The University of Osaka, Suita, Japan; 2Research Center for UHVEM, The University of Osaka, Ibaraki, Japan
Recently, ultra-small sized optical and electronic devices have actively been developing, and evaluation of ultrafast carrier recombination processes on semiconductor surfaces is important technique to control the device performances. Time-resolved photoluminescence spectroscopy is typically used to characterize carrier recombination lifetime in semiconductors. However, the detected signals include information from both surface and bulk states due to penetration depth of the excitation light. Time-resolved two-photon photoemission (Tr-2PPE) spectroscopy can be a novel technique to directly detect excess electrons as photoelectrons emitted from sample surfaces. In this approach, the first pulsed-light excites electrons from a valence band to a conduction band, and the second pulse ionizes the excited-electrons beyond a vacuum level after controlled time-delay. The detected signals are limited by surface carriers due to the short electron mean free paths (less than several nanometers). In this work, we report on the analyses of surface recombination of semiconductors based on the Tr-2PPE spectroscopy, where InGaN and GaAs are evaluated as examples, and show a strong impact of surface conditions on the surface on carrier recombination processes.
FK-3:IL15 Combining Cathodoluminescence and Photoluminescence in-situ in the SEM for the analysis of semiconducting materials
F. ROSSI, L. NASI, E. FERRARI, L. POLETTI, IMEM-CNR Institute, Parma, Italy
Cathodoluminescence (CL) and photoluminescence (PL) are complementary techniques that provide valuable insights into the optical and electronic properties of semiconducting materials. CL offers (sub)micrometric spatial resolution, tunable penetration depth and direct correlation with local structural features, while PL probes the material via optical excitation under controlled conditions with high spectral resolution. In this lecture, we present a novel experimental setup that integrates CL and PL in situ within a scanning electron microscope (SEM). This configuration allows combining or switching between electron- and photon-induced excitation on the same region of interest, enabling direct comparison of emission mechanisms and defect-related phenomena. The system supports both spectroscopy and hyperspectral mapping, in a wide temperature range (from RT down to cryogenic temperature), providing a temperature-dependent comprehensive characterization of band-edge and defect-related emissions with high spatial and spectral resolution. Applications to various semiconducting systems will be discussed, highlighting the advantages of this correlative approach for understanding light–matter interactions at the nanoscale and guiding the development of advanced optoelectronic materials.
FK-3:L15b High-Pressure Engineering of LiGaO2:Ni2+ for the Design of SWIR Phosphors
M. KAMINSKI1, MU-HUAI FANG2, S. MAHLIK1, 1Institute of Experimental Physics, Faculty of Mathematic, Physics, and Informatics, University of Gdańsk, Gdańsk, Poland; 2Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
High-pressure engineering offers a powerful route to activate and tailor the optical properties of transition-metal-based phosphors beyond the limitations of ambient-pressure crystal chemistry. Here, we demonstrate that applying pressure to LiGaO2:Ni2+ induces a structural transformation that stabilizes Ni2+ ions in an octahedral coordination environment, enabling intense broadband shortwave infrared (SWIR) emission originating from the spin-allowed 3T2 → 3A2 transition of the d8 configuration. In contrast, the ambient-pressure phase remains optically inactive. Temperature- and pressure-dependent photoluminescence, excitation, and lifetime measurements combined with crystal-field analysis reveal a weak octahedral crystal field, moderate electron-lattice coupling, and pressure-dependent evolution of the Racah parameters. Incorporating this evolution exposes a key limitation of conventional Tanabe–Sugano diagrams, showing that the commonly anticipated 1E – 3T2 crossover is shifted to much higher pressures or becomes inaccessible. The unexpected increase of the Racah parameter B under pressure indicates enhanced localization of Ni2+ 3d electrons and reduced metal–ligand covalency. These findings establish high-pressure engineering as an effective strategy for designing broadband Ni2+-based SWIR phosphors.
Session FK-4 Device architectures and system integration
FK-4:IL16 InGaN-based Light Emitters and Down-converting Luminescent Wide-field-of-view Receivers for Optical Wireless Communications
BOON S. OOI, Electrical, Computer, and Systems Engineering (ECSE) Rensselaer Polytechnic Institute (RPI), USA and Electrical and Computer Engineering (ECE) King Abdullah University of Science and Technology (KAUST), KSA
Optical wireless communication (OWC), including visible light communication (VLC or LiFi), has emerged as a key enabler for future high-capacity wireless networks. Since its conceptual introduction in 2011, VLC has advanced from proof-of-concept demonstrations with data rates of a few hundred Mbps using InGaN-based LEDs, to Gbps-class systems driven by high-speed micro-LED and laser technologies. Recent deployments of multi-Gbps VLC links demonstrate the potential of compact, energy-efficient, and spectrally unconstrained optical systems. A major challenge for practical OWC remains the stringent alignment between transmitters and receivers, arising from the trade-off between detector active area and response speed, which typically necessitates narrow field-of-view (FoV) optics. To address this, we have recently developed a new class of wide-FoV detectors that relax the alignment requirement while maintaining high-speed response. Such advances open pathways toward robust, alignment-free OWC systems. In this paper, we will discuss recent progress in InGaN-based high-speed lasers and wide-FoV detectors and highlight their role in enabling next-generation OWC systems that combine high data rates with practical deployment flexibility.
FK-4:IL17 Far-UV-C Light-emitting Diodes for Optical Wireless Communications
M.D. DAWSON, Institute of Photonics, University of Strathclyde Technology & Innovation Centre, Glasgow, UK
The distinctive properties of UV-C light offer attractive opportunities for novel optical wireless communications, including line-of-sight (LOS) links with minimal solar background, non-line-of-sight (NLOS) links mediated by atmospheric scattering, and intersatellite links not visible from the ground. Recent advances in AlGaN semiconductor based light-emitting diodes (LEDs) are resulting in new optical device technologies for this UV-C range, with wavelength coverage, device efficiencies and other key aspects of performance improving all the time. Here, we report our progress in developing micro-LED formats of such devices - LEDs with pixel size of a few 10's of micrometres - in this wavelength range and applying them to optical wireless communications. Device wavelengths in the UV-C between 235nm and 280nm have been explored, and the micro-LEDs investigated when operating under advanced data encoding techniques to demonstrate LOS links at Gb/s data rates over tens of metre distances. Clusters of devices of differing wavelength have also been developed and applied to demonstrate coarse wavelength division multiplexing (CWDM) in the ultraviolet. We will summarise these results, together with highlighting current trends and new opportunities for this rapidly emerging technology.
FK-4:IL18 Hollow Core Fiber: A New Way to Guide Light in the Air
F. MELLI, L. VINCETTI, Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Modena, Italy
Thirty years after their conception, Hollow-Core Photonic Crystal Fibers (HC-PCFs) have revolutionized fiber-optic technology by surpassing the loss limits of solid-core fibers over a spectral range extending from the ultraviolet to THz, thanks to light propagation in a hollow core. These fibers can be filled with gases or liquids, making them ideal platforms for nonlinear and quantum optics. The absence of solid material in the core minimizes optical damage and eliminates nonlinearity, thereby greatly improving power handling and enabling high-capacity communication systems. Among the various types of HC-PCFs, Inhibited-Coupling HC-PCFs (IC-HCPCFs) currently represent the most promising and best-performing solution. Unlike Photonic Bandgap HC-PCFs, IC-HCPCFs do not rely on a cladding that forbids radial propagation of light. Their waveguiding mechanism, however, remains a subject of debate within the scientific community. In this work, we address this issue by proposing a unified model. Our findings provide a long-missing design framework that clarifies the ultimate limits of current geometries and equips fiber designers with predictive tools to evaluate and minimize loss contributions. This opens new avenues for the further advancement of IC-HCPCFs technologies.