Graphene quantum dots (GQDs) have attracted great attention as next-generation luminescent nanomaterials due to the advantages of a low-cost process, low toxicity, and unique photoluminescence (PL). However, in the solid-state, the strong π−π stacking interactions between the basal planes of GQDs lead to aggregation-caused PL quenching (ACQ), which impedes practical application to light-emitting devices. Here, surface functionalized GQDs (F-GQDs) by polyhedral oligomeric silsesquioxane (POSS), poly(ethylene glycol) (PEG), and hexadecylamine (HDA) to reduce π−π stacking-induced ACQ is presented. The POSS-, PEG-, and HDA-functionalized GQDs show a significant enhancement in PL intensity compared to bare GQDs by 9.5-, 9.0-, and 5.6-fold in spin-coated film form and by 8.3-, 7.2-, and 3.4-fold in drop-casted film form, respectively. Experimental results and molecular dynamics simulations indicate that steric hindrance of the functionalization agent contributes to reducing the π−π stacking between adjacent GQDs and thereby enabling quenching-resistant PL in the solid-state. Moreover, the GQD-based white light-emitting diodes fabricated by mounting HDA-GQDs on a UV-LED chip exhibits efficient downconversion for white light emission with a high color rendering index of 86.2 and a correlated-color temperature of 5612 K at Commission Internationale de l'Éclairage coordinates of (0.333, 0.359).

Cross‐point arrays of synaptic devices have been investigated as a core platform for neuromorphic computing architectures. To achieve a significant speed boost in deep neural network computations compared to the von Neumann architecture, it is essential to develop synaptic devices with optimal performance for fully parallel vector‐matrix‐multiplication. Among various non‐volatile memory candidates, metal‐oxide based electrochemical random‐access memory (ECRAM) is considered as a promising analog synapse due to its superior switching characteristics and CMOS‐compatibility. However, the switching mechanisms of metal‐oxide ECRAM remain to be understood, impeding improvements of the synaptic characteristics and device performance. Here, ionic programming dynamics based on oxygen ion migration and associated redox‐reactions are investigated in metal‐oxide ECRAMs by considering ion transport via the electrolyte and diffusion in the channel. Additionally, the origins of update asymmetry and long‐term retention found in voltage‐pulse programming measurements are explained by non‐uniform distribution of the off‐stoichiometry in the channel layer. By exploiting the programming mechanism, ECRAMs can achieve desirable synaptic characteristics under voltage‐pulse mode. Finally, experimental and simulation studies consistently suggest that channel and electrolyte with high ionic transport properties can improve the performance of metal‐oxide ECRAMs, opening a path toward optimized synaptic device characteristics for the maximum computation performance.

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