We find that the emission from laterally coupled quantum dots is strongly polarized along the coupled direction [1 $$\bar 1$$1 ¯ 0], and its polarization anisotropy can be shaped by changing the orientation of the polarized excitation. When the nonresonant excitation is linearly polarized perpendicular to the coupled direction [110], excitons (X₁ and X₂) and local biexcitons (X₁X₁ and X₂X₂) from the two separate quantum dots (QD₁ and QD₂) show emission anisotropy with a small degree of polarization (10%). On the other hand, when the excitation polarization is parallel to the coupled direction [1 $$\bar 1$$1 ¯ 0], the polarization anisotropy of excitons, local biexcitons, and coupled biexcitons (X₁X₂) is enhanced with a degree of polarization of 74%. We also observed a consistent anisotropy in the time-resolved photoluminescence. The decay rate of the polarized photoluminescence intensity along the coupled direction is relatively high, but the anisotropic decay rate can be modified by changing the orientation of the polarized excitation. An energy difference is also observed between the polarized emission spectra parallel and perpendicular to the coupled direction, and it increases by up to three times by changing the excitation polarization orientation from [110] to [1 $$\bar 1$$1 ¯ 0]. These results suggest that the dipole–dipole interaction across the two separate quantum dots is mediated and that the anisotropic wavefunctions of the excitons and biexcitons are shaped by the excitation polarization.

Micro-photoluminescence was observed while increasing the excitation power in a single GaAs quantum ring (QR) at 4 K. Fine structures at the energy levels of the ground (N = 1) and excited (N = 2) state excitons exhibited a blue shift when excitation power increased. The excited state exciton had a strong polarization dependence that stemmed from the asymmetric localized state. According to temperature-dependence measurements, strong exciton–phonon interaction (48 meV) was observed from an excited exciton state in comparison with the weak exciton–phonon interaction (27 meV) from the ground exciton state, resulting from enhanced confinement in the excited exciton state. In addition, higher activation energy (by 20 meV) was observed for the confined electrons in a single GaAs QR, where the confinement effect was enhanced by the asymmetric ring structure.

Graphene quantum dots (GQDs) exhibit complex photoluminescence (PL) originating from intrinsic sp ² carbon domains, surface functional groups, and structural defects. Yet the spectral overlap among these emissive channels hinders clear identification of their recombination pathways. Here, we investigate multichannel PL dynamics of commercial GQDs using time‐resolved and cryogenic PL spectroscopy. PL spectra reveal three distinct peaks: Peak I (443 nm) from π–π* transitions, Peak II (520 nm) from surface‐dominated contribution functional states, and Peak III (583 nm) from pyrrolic N‐related defects. Time‐correlated single‐photon counting detects only a 460 nm emission linked to graphitic N traps, indicating that Peaks I–III decay faster than the nanosecond window. Ultrafast optical Kerr‐gate measurements further resolve distinct lifetimes for hydroxyl (<5 ps), carboxyl (5–10 ps), amine (20–30 ps), and carbonyl (40–80 ps) groups. The transient evolution displays cascade relaxation from deep to shallow traps, evidenced by a progressive blue‐shift of Peak II. Cryogenic PL shows stable emission of Peak I, whereas Peak III red‐shifts and broadens with temperature, revealing strong electron–phonon coupling and deep‐level trapping. These results clarify the multichannel emission mechanisms of GQDs and provide design principles for tuning their optical properties.

You Ryang Seo, Taein Kang, Jong Su Kim, Jin Dong Song, Sang Jun Lee, and Heedae Kim. Applied Science and Convergence Technology 2023;32:12-5. https://doi.org/10.5757/ASCT.2023.32.1.12

Heedae Kim and Keun Heo. Applied Science and Convergence Technology 2023;32:38-40. https://doi.org/10.5757/ASCT.2023.32.2.38