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1. Temperature‐Dependent Optical and Polaritonic Properties of Excitons in hBN‐Encapsulated Monolayer TMDs

   https://doi.org/10.1002/adom.202502535  

   Meshulam, Matan; Kahlon, Anabel Atash; Gershuni, Yonatan; Poirier, Thomas; Edgar, James H; Tongay, Seth Ariel; Epstein, Itai (February 2026, Advanced Optical Materials)

   Abstract Monolayer transition metal dichalcogenides (TMDs) support robust excitons in the visible to near‐infrared spectral range. Their reduced dielectric screening results in large binding energies, and combined with a direct bandgap in monolayer form, these excitons dominate the optical response of TMDs. In this work, a comprehensive investigation of the temperature‐dependent optical and polaritonic properties of high‐quality WS₂, MoS₂, WSe₂, and MoSe₂monolayers, encapsulated by hBN, in the range of 5‐300 K, is presented. Using reflection spectroscopy measurements, the optical and polaritonic constituents of the TMD excitons in terms of oscillator strength, linewidth, and negative permittivity, are evaluated and compared. It is found that MoSe₂exhibits the most pronounced optical and polaritonic response, stemming from its rapid linewidth narrowing at low temperatures, as compared to the other TMDs. In addition, It is found that all four TMDs exhibit a temperature‐dependent negative real part permittivity, thus supporting surface‐exciton‐polaritons. The dispersion relation, confinement factor, and losses are derived and similarly reveal that MoSe₂exhibits enhanced polaritonic properties. These findings establish a comparative framework for understanding the optical and polaritonic properties of monolayer TMDs, with implications on their utilization in optoelectronic devices based on 2D semiconductors. 

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2. Photoswitchable optoelectronic properties of 2D MoSe2/diarylethene hybrid structures

   https://doi.org/10.1038/s41598-024-57479-z  

   Park, Sewon; Ji, Jaehoon; Cunningham, Connor; Pillai, Srajan; Rouillon, Jean; Benitez-Martin, Carlos; Fang, Mengqi; Yang, Eui-Hyeok; Andréasson, Joakim; You, Jeong Ho; et al (December 2024, Scientific Reports)

   Abstract The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe₂with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe₂, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe₂, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe₂to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe₂. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe₂/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices. 

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3. Dimensionality and Anisotropicity Dependence of Radiative Recombination in Nanostructured Phosphorene

   https://doi.org/10.1039/C9TC02214G  

   Wu, Feng; Rocca, Dario; Ping, Yuan (January 2019, Journal of Materials Chemistry C)

   The interplay between dimensionality and anisotropicity leads to intriguing optoelectronic properties and exciton dynamics in low dimensional semiconductors. In this study we use nanostructured phosphorene as a prototypical example to unfold such complex physics and develop a general first-principles framework to study exciton dynamics in low dimensional systems. Specifically we derived the radiative lifetime and light emission intensity from 2D to 0D systems based on many body perturbation theory, and investigated the dimensionality and anisotropicity effects on radiative recombination lifetime both at 0 K and finite temperature, as well as polarization and angle dependence of emitted light. We show that the radiative lifetime at 0 K increases by an order of 103 with the lowering of one dimension (i.e. from 2D to 1D nanoribbons or from 1D to 0D quantum dots). We also show that obtaining the radiative lifetime at finite temperature requires accurate exciton dispersion beyond the effective mass approximation. Finally, we demonstrate that monolayer phosphorene and its nanostructures always emit linearly polarized light consistent with experimental observations, different from in-plane isotropic 2D materials like MoS2 and h-BN that can emit light with arbitrary polarization, which may have important implications for quantum information applications. 

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4. Effects of Size, Shape, and Functionalization on the Electronic and Optical Properties of Carbon Quantum Dots

   https://doi.org/10.1149/MA2026-0110879mtgabs  

   Duong, Quang Quy; Kilin, Dmitri S; Rasulev, Bakhtiyor (July 2026, ECS Meeting Abstracts)

   Carbon quantum dots (CQDs) have attracted significant interest due to their tunable electronic and optical properties. In this study, we examine how nanoscale size, geometry, and edge functionalization govern these properties. A systematic set of triangular and hexagonal armchair graphene nanoflakes was constructed and analyzed using DFT and TDDFT. The lowest excitation energy (gaps) uniformly decrease with increasing radius due to weakened quantum confinement, with triangular CQDs exhibiting consistently larger gaps than hexagonal ones at equal physical size. Certain size of CQD exhibits near infrared optical activity. Quantitative size–gap relationships were established, enabling the prediction of energy-gap dependence due to quantum confinement. A nearly perfect linear correlation between PBE and HSE06 gaps (R²= 0.99) allows accurate prediction of hybrid-functional results from inexpensive PBE calculations. Optical absorption spectra reveal a pronounced size-dependent red shift and geometry-dependent variations in oscillator strength. Reported results demonstrate confinement-related size scaling of gap deviation from Bruce law due to graphitic nature and specifics of edge of the flake geometry. The contribution of exciton binding energy to the gap is analyzed. In addition, electron donating NH₂functionalization is found to contribute additional states, significantly modulate oscillator strengths, with appropriately designed substitution patterns leading to enhanced intensity of both absorption and emission intensity. Comparison with experimental data¹for triangular CQDs shows agreement in transition energies, intensity, and spectral profile. A QSPR model is established to correlate gap and oscillator strength with structural features of CQDs. These results help to understand mechanisms how size, shape, and functionalization engineering provide effective levers for tuning CQD’s optoelectronic behavior. Acknowledgement:D.K. thanks NSF CHE-1944921 for support of quantum dynamics methods development. B.R. acknowledges support of DOE DE-SC0021287 and DOE DE-SC0022239 for computational modeling of infrared emitters. Reference:(1) Yuan, F., Yuan, T., Sui, L., Wang, Z., Xi, Z., Li, Y., Li, X., Fan, L., Tan, Z. a., Chen, A.; et al. Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs.Nature Communications2018,9, 2249. 

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5. Controlling exciton transport in monolayer MoSe ₂ by dielectric screening

   https://doi.org/10.1039/C9NH00462A  

   Hao, Shengcai; Bellus, Matthew Z.; He, Dawei; Wang, Yongsheng; Zhao, Hui (January 2020, Nanoscale Horizons)

   Due to their atomic thinness with reduced dielectric screening, two-dimensional materials can possess a stable excitonic population at room temperature. This is attractive for future excitonic devices, where excitons are used to carry energy or information. In excitonic devices, controlling transport of the charge-neutral excitons is a key element. Here we show that exciton transport in a MoSe 2 monolayer semiconductor can be effectively controlled by dielectric screening. A MoSe 2 monolayer was partially covered with a hexagonal boron nitride flake. Photoluminescence measurements showed that the exciton energy in the covered region is about 12 meV higher than that in the uncovered region. Spatiotemporally resolved differential reflection measurements performed at the junction between the two regions revealed that this energy offset is sufficient to drive excitons across the junction for about 50 ps over a distance of about 200 nm. These results illustrate the feasibility of using van der Waals dielectric engineering to control exciton transport and contribute to understanding the effects of the dielectric environment on the electronic and optical properties of two-dimensional semiconductors. 

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