Traditionally, organic luminescent materials have been classified based on their ability to exhibit either fluorescence or phosphorescence, two fundamentally different types of light emission originating from distinct excited-state processes. Fluorescence involves the prompt emission of photons as excited electrons return to the ground state, typically within nanoseconds. In contrast, phosphorescence arises from the slower relaxation of electrons trapped in a triplet excited state, extending emission lifetimes into microseconds and beyond. The ability to simultaneously manipulate both these emissive pathways within a single material platform has long challenged scientists due to the conflicting time scales and spin multiplicities involved.

The research team addressed this challenge by designing an organic luminescent system that strategically incorporates multiple excited states, thereby enabling efficient intersystem crossing and reverse intersystem crossing mechanisms in tandem. By fine-tuning the molecular architecture, they successfully achieved a material where delayed fluorescence—a form of thermally activated delayed fluorescence (TADF)—and phosphorescence coexist. This dual emission process was demonstrated under ambient conditions, a critical criterion for practical applications.

Central to this revelation is the molecular engineering that balances singlet and triplet excited states, allowing the material to harness triplet excitons that traditionally remain non-radiative or contribute to phosphorescence only. In this system, the conversion of triplet excitons back to singlet states facilitates delayed fluorescence. Concurrently, a portion of the triplet population emits directly through phosphorescence. The concurrency of these radiative decay channels is meticulously controlled through quantum yield optimization and excited state energy alignment.

The implications of this discovery extend beyond fundamental photophysics to real-world applications. Organic light-emitting diodes (OLEDs), a technology increasingly pervasive in modern display and lighting systems, stand to benefit significantly. By leveraging both delayed fluorescence and phosphorescence, devices can attain higher internal quantum efficiencies without relying on heavy metal dopants, which are not only costly but pose environmental concerns. This all-organic approach promises more sustainable and efficient OLED designs.

Moreover, the ability to tune the emission via multiple excited states opens new possibilities for color purity and tunability in lighting applications. Traditional phosphorescent materials often suffer from spectral broadening or color instability, while pure fluorescence emitters may lack efficiency. The dual mechanism stabilizes emission profiles and enhances brightness, potentially enabling customizable, high-resolution displays and adaptive lighting systems responsive to environmental inputs.

In the realm of bioimaging, organic compounds exhibiting prolonged emission lifetimes, namely through delayed fluorescence and phosphorescence, can significantly improve imaging resolution and contrast by minimizing background fluorescence. This allows for time-gated imaging techniques that isolate the desired luminescent signals, an advantage this new material system could amplify, offering more sensitive diagnostic tools and real-time bio-probes.

The authors employed an array of spectroscopic techniques to unravel the material’s excited-state dynamics, including time-resolved photoluminescence and transient absorption measurements, validating the coexistence of delayed fluorescence and phosphorescence with distinct temporal profiles. Their rigorous characterization ensures that the observed dual emission is intrinsic to the molecular design rather than an artifact of environmental variations or impurities.

Additionally, computational studies using quantum chemical calculations provided insight into the energy landscape and spin-orbit coupling effects governing intersystem crossing rates. The simulations guided the rational design of molecular entities with appropriate singlet-triplet energy gaps, a critical parameter for efficient reverse intersystem crossing that underpins delayed fluorescence.

This research represents a paradigm shift in the understanding and utilization of organic luminescent materials. By demonstrating control over multiple excited states to enable concurrent delayed fluorescence and phosphorescence, it redefines the boundaries of organic optoelectronics. The ability to engineer materials with tailored emission kinetics and spectral properties unlocks synergies previously deemed incompatible within a single molecular platform.

Future directions proposed by the team include expanding the molecular library of such dual-emissive compounds and integrating these materials into functional devices to test performance under operational conditions. They highlight the promise of this approach not only in OLEDs but also in organic lasers, sensing devices, and luminescent solar concentrators, suggesting a broad technological impact.

Challenges remain, particularly in scaling synthesis, ensuring long-term stability, and optimizing emission efficiency across the visible spectrum. However, the foundational knowledge established in this study offers a research roadmap toward overcoming these hurdles. Collaborative efforts bridging chemistry, physics, and engineering will be pivotal in translating this molecular innovation into commercial products.

In essence, Dou and colleagues’ breakthrough underscores the power of rational molecular design combined with mechanistic insight to circumvent limitations inherent in organic luminescent materials. This work exemplifies how a nuanced understanding of excited-state multiplicities and their interplay can be leveraged to craft materials with unprecedented photophysical properties, influencing a spectrum of scientific and industrial fields.

As the demand for sustainable, efficient, and versatile lighting and display technologies intensifies, such advances underscore the critical role of fundamental science in driving innovation. The confluence of delayed fluorescence and phosphorescence within a singular organic emitter charts a new course for the next generation of luminescent materials, heralding a future where organic electronics can achieve previously unattainable levels of performance and functionality.

Subject of Research:
Organic luminescent materials exhibiting simultaneous delayed fluorescence and phosphorescence through multiple excited states.

Article Title:
Simultaneous delayed fluorescence and phosphorescence in organic luminescent material employing multiple excited states.

Article References:
Dou, D., Liu, W., Zhou, X. et al. Simultaneous delayed fluorescence and phosphorescence in organic luminescent material employing multiple excited states. Light Sci Appl 15, 4 (2026). https://doi.org/10.1038/s41377-025-02063-x

Image Credits:
AI Generated

DOI:
01 January 2026

At the heart of this discovery lies the delicate interplay between 2D excitons and plasmonic nanostructures. Excitons, quasiparticles representing bound electron-hole pairs, exhibit remarkable optical properties when confined in atomically thin semiconductor layers. These 2D materials, characterized by their reduced dimensionality, offer enhanced Coulomb interactions and markedly increased binding energies, enabling pronounced excitonic effects even at room temperature. By embedding such excitons within a nanocavity engineered to embrace dual resonances, the research team has effectively amplified nonlinear optical processes, resulting in an unprecedented efficiency of two-photon upconversion.

Two-photon upconversion refers to the nonlinear optical process where two photons of lower energy are simultaneously absorbed, combining their energies to emit a single photon of higher energy. This phenomenon, highly coveted in photonics for its potential in frequency conversion and bioimaging, is typically hampered by inefficiencies due to the need for strict phase matching and weak light-matter coupling in conventional materials. Overcoming such limitations demands strategic engineering at the nanoscale, a challenge adeptly addressed by leveraging the plasmonic nanocavity’s unique capabilities in this study.

The doubly-resonant plasmonic nanocavity constructed by the authors exhibits two discrete resonance modes precisely matched to both the excitation and emission wavelengths involved in the two-photon process. This carefully tuned resonator design ensures that the local electromagnetic fields at these frequencies are intensely confined and significantly enhanced, boosting the interaction strength between the incident photons and 2D excitons. Such dual resonance not only magnifies the absorption probability but also facilitates efficient emission, thereby optimizing the entire upconversion cycle.

Material-wise, the choice of 2D semiconductor material is pivotal. The research utilized monolayer transition metal dichalcogenides (TMDs), a class of 2D semiconductors known for their direct bandgaps and pronounced excitonic resonances in the visible spectrum. These properties allow the 2D excitons to couple strongly with the localized surface plasmons generated within the metallic nanocavity, resulting in a remarkable interplay that profoundly influences the nonlinear optical response. This strong coupling regime is instrumental in realizing the giant upconversion effect reported.

From an experimental perspective, the authors meticulously fabricated and characterized the doubly-resonant nanocavities, employing advanced nanolithography techniques to achieve nanoscale precision in cavity dimensions. Structural characterization confirmed the cavity’s geometric parameters, while spectral measurements validated the dual resonance modes’ positions. Subsequent nonlinear optical experiments revealed an extraordinary enhancement in two-photon upconversion efficiency—orders of magnitude greater than in isolated 2D materials or conventional plasmonic systems lacking such resonance engineering.

The mechanics behind this giant upconversion can be understood through the concept of Purcell enhancement, where the spontaneous emission rate of an emitter—here, the 2D exciton—is amplified by its photonic environment. In the doubly-resonant plasmonic nanocavity, the local density of optical states is tailor-made, leading to a synergistic enhancement of both two-photon absorption and exciton radiative recombination. This synergy culminates in a nonlinear optical process of unprecedented scale and efficiency, which until now had been largely theoretical.

The implications of these findings are vast and multifaceted. In the realm of optical computing and telecommunications, the ability to convert photons across different energies with high efficiency and at the nanoscale can lead to novel, compact photonic devices capable of ultrafast signal processing and wavelength multiplexing. Furthermore, applications in bioimaging stand to benefit greatly, as two-photon upconversion enables deeper tissue penetration with reduced photodamage, promising advancements in medical diagnostics and live imaging techniques.

Another notable facet of this work is the potential to integrate such 2D exciton-plasmonic nanocavity systems with emerging quantum technologies. Nonlinear optical processes are central to generating entangled photon pairs and single-photon sources, essential components for quantum cryptography and computing. Here, the giant two-photon upconversion response could serve as a platform for efficient quantum light sources at room temperature, significantly advancing practical quantum photonics.

Beyond the immediate technological landscape, the study provides crucial insights into the fundamental physics governing light-matter interactions in reduced dimensions under extreme confinement. Understanding how excitons behave and interact with plasmonic fields opens new avenues for exploring exciton-polariton phenomena, many-body interactions, and quantum coherence effects in 2D heterostructures, which remain at the frontier of condensed matter physics and nanophotonics.

The research also highlights the importance of precise nanofabrication and materials synthesis to tailor the optical environment rigorously. Achieving doubly-resonant conditions demands a harmonious balance between cavity design, material choice, and experimental conditions—a triad that, when optimized, unlocks phenomena previously unattainable in single-resonance or less controlled settings.

Looking ahead, the team envisions that their approach can be generalized to other 2D materials and hybrid nanostructures, paving the way for customizable nonlinear optical devices operating across a broad spectral range. This adaptability is crucial as photonic technologies evolve towards multifunctional, integrable platforms for sensing, energy harvesting, and information processing.

Moreover, this giant two-photon upconversion mechanism can inspire new strategies for enhancing other nonlinear processes such as harmonic generation and four-wave mixing in 2D systems, further expanding the toolkit for engineering light at the nanoscale. As such, the findings are not confined to a single phenomenon but rather illuminate a broader paradigm of nanoscale nonlinear optics capability.

In sum, the study presents a compelling demonstration of how meticulously engineered plasmonic nanocavities can unlock extraordinary nonlinear optical phenomena in atomically thin semiconductors. By marrying the unique excitonic properties of 2D materials with the electromagnetic prowess of plasmonics, this research sets a new benchmark for photonic device performance, promising a future where light manipulation at the quantum level is both practical and scalable.

This breakthrough not only enriches the fundamental understanding of exciton-plasmon coupling but also propels the field towards real-world applications, signalling an exciting era where two-photon upconversion and related nonlinear processes are harnessed with unprecedented efficiency, fidelity, and versatility.

As the scientific community digests the full impact of these findings, further explorations into tuning resonance conditions, improving material quality, and integrating such nanocavities in device architectures will undoubtedly accelerate the transition from proof-of-concept demonstrations to impactful technologies shaping the next generation of photonic systems.

Subject of Research: Giant two-photon upconversion from 2D excitons in a doubly-resonant plasmonic nanocavity

Article Title: Giant two-photon upconversion from 2D exciton in doubly-resonant plasmonic nanocavity

Article References:
Liu, F., Liu, H., Chi, C. et al. Giant two-photon upconversion from 2D exciton in doubly-resonant plasmonic nanocavity. Light Sci Appl 14, 312 (2025). https://doi.org/10.1038/s41377-025-02010-w

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41377-025-02010-w