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We have developed an ab initio-based, fully quantum, numerically accurate methodology for the simulation of the exciton dynamics and time- and frequency-resolved fluorescence spectra of the cavity-controlled two-dimensional materials at finite temperatures and applied this methodology to the single-layer WSe2 system. Specifically, the multiple Davydov D2 Ansatz has been employed in combination with the method of thermofield dynamics for the finite-temperature extension of accurate time-dependent variation. This allowed us to establish dynamical and spectroscopic signatures of the polaronic and polaritonic effects as well as uncover their characteristic time scales in the relevant range of temperatures. Our study reveals the pivotal role of multidimensional conical intersections in controlling the many-body dynamics of highly intertwined excitonic, phononic, and photonic modes. Ministry of Education (MOE) Submitted/Accepted version The authors gratefully acknowledge the support of the Singapore Ministry of Education Academic Research Fund (Grant Nos. RG190/18 and RG87/20). K. Sun would also like to thank the Natural Science Foundation of Zhejiang Province (Grant No. LY18A040005) for partial Support. M. F. G. acknowledges the support of Hangzhou Dianzi University through startup funding.

The multimode Brownian oscillator model is employed to simulate the emission spectra of transition metal dichalcogenide (TMD) monolayers. Good agreement is obtained between measured and simulated photoluminescence spectra of WSe2, WS2, MoSe2, and MoS2 at various temperatures. The Huang-Rhys factor extracted from the model can be associated with that from the modified semiempirical Varshni equation at high temperatures. Individual mechanisms leading to the unique temperature-dependent emission spectra of those TMDs are validated by the multimode Brownian oscillator (MBO) fitting, while it is, in turn, confirmed that the MBO analysis is an effective method for studying the optical properties of TMD monolayers. Parameters extracted from the MBO fitting can be used to explore exciton-photon-phonon dynamics of TMDs in a more comprehensive model. Ministry of Education (MOE) Submitted/Accepted version The authors gratefully acknowledge the support of the Singapore Ministry of Education Academic Research Fund (grant nos. RG190/18 and RG87/20). K.S. would also like to thank the Natural Science Foundation of Zhejiang Province (grant no. LY18A040005) for partial support.

Halide perovskites are revolutionizing the renewable energy sector owing to their high photovoltaic efficiency, low manufacturing cost, and flexibility. Their remarkable mobility and long carrier lifetime are also valuable for information technology, but fundamental challenges like poor stability under an electric field prevent realistic applications of halide perovskites in electronics. Here, it is discovered that valleytronics is a promising route to leverage the advantages of halide perovskites and derivatives for information storage and processing. The synthesized all-inorganic lead-free perovskite derivative, Cs3 Bi2 I9 , exhibits strong light-matter interaction and parity-dependent optically addressable valley degree of freedom. Robust optical helicity in all odd-layer-number crystals with inversion symmetry breaking is observed, indicating excitonic coherence extending well beyond 11 layers. The excellent optical and valley properties of Cs3 Bi2 I9 arise from the unique parallel bands, according to first principles calculations. This discovery points to new materials design principles for scalable valleytronic devices and demonstrates the promise of perovskite derivatives beyond energy applications.

To determine the causes of a severe haze episode in January 2013 in China, a source apportionment of different carbonaceous aerosols (CAs) was conducted in a megacity in central China (Wuhan, Hubei Province) by using the measurements of radiocarbon and molecular organic tracers. Non-fossil sources (e.g., domestic biofuel combustion and biogenic emissions) were found to be responsible for 62% ± 5% and 26% ± 8% of organic carbon (OC) and elemental carbon (EC) components by mass, respectively. Non-fossil sources contributed 57% ± 4% to total CAs in this large-scale haze event, whereas fossil-fuel sources were less dominant (43% ± 4%). The CAs were composed of secondary organic carbon (SOC; 46% ± 10%), primary fossil-fuel carbon (29% ± 4%) and primary biomass-burning carbon (25% ± 10%). Although SOC was formed mainly from non-fossil sources (70% ± 4%), the role of fossil precursors was substantial (30% ± 4%), much higher than at the global scale. Combined measurement of organic tracers and radiocarbon showed that most non-fossil SOC was probably derived from biomass burning during this long-lasting haze episode in central China.

We conducted a source apportionment and investigated the atmospheric behavior of carbonaceous aerosols during hazy and normal days using radiocarbon ((14)C) and biomass burning/secondary organic aerosol (SOA) tracers during winter in Guangzhou, China. Haze episodes were formed either abruptly by local emissions or through the accumulation of particles transported from other areas. The average contributions of fossil carbon to elemental carbon (EC), water-insoluble organic carbon, and water-soluble organic carbon were 71 ± 10%, 40 ± 6% and 33 ± 3%, respectively. High contributions of fossil carbon to EC (80-90%) were observed for haze samples that were substantially impacted by local emissions, as were the highest (lowest) ratios for NO3(-)/SO4(2-) (OC/EC), which indicates that these particles mainly came from local vehicle exhaust. Low contributions of fossil carbon to EC (60-70%) were found for haze particles impacted by regional transport. Secondary organic carbon (SOC) calculated using SOA tracers accounts for only ∼ 20% of the SOC estimated by (14)C, which is probably because some important volatile organic carbons are not taken into account in the SOA tracer calculation method and because of the large discrepancy in ambient conditions between the atmosphere and smog chambers. A total of 33 ± 11% of the SOC was of fossil origin, a portion of which could be influenced by humidity.

The concentrations of halogenated flame retardants (HFRs) in PM2.5 were monitored for one year at 10 urban sites in China during 2013-2014. This study investigated four classes of HFRs: nine polybrominated diphenyl ethers (PBDEs), six nonbromodiphenyl ether (BDE) brominated flame retardants, two dechlorane plus (DP) flame retardants, and three chlorinated organophosphate flame retardants (OPFRs). Extremely high concentrations of BDE-209 and DBDPE were observed in only one city (Guangzhou), which was a consequence of the intensive e-waste recycling and disposal operations in the Pearl River Delta. This result differed from the tris(monochloropropyl) phosphate (TCPP) and tris(2-chloroethyl) phosphate (TCEP) distributions, which showed high concentrations in most cities, suggesting wide usage and large emissions in China in recent years. The highest TCPP and TCEP concentrations were observed in the summer, indicating that emission from local sources was an important factor controlling the levels in the air. This was not the case for BDE-209 and DBDPE, for which higher concentrations were found in winter. When bound to particulate matter due to low vapor pressure, these compounds may be more persistent in air, and temperature-dependent gas-particle partitioning was a key factor. Moreover, regional pollution and long-range transport had a significant influence on the seasonal distributions of BDE-209 and DBDPE, especially in cities (Guangzhou and Shanghai) close to electrical/electronic waste recycling sites. Residents in urban areas were exposed to higher levels of chlorinated OPFRs. This raises considerable concern, and an appropriate risk assessment is required.