Lanthanide-doped upconversion nanoparticles (UCNPs) have been extensively investigated owing to their unique advantages. So far, the most favored modality of UCNPs is still the classical Yb–A (where A refers to Er 3+ , Tm 3+ , and Ho 3+ )-coupled nanosystems under 980-nm excitation. However, the frequently used Yb 3+ ion with the single-excited 2 F 5/2 state can barely transfer energy to other acceptors owing to its lack of matched excited levels. Herein, a novel strategy is proposed for energy transfer via Ho 3+ as a bridge ion coupling donor-acceptor pairs (e.g., Yb 3+ –Nd 3+ ), where little direct energy transfer occurs, and the involved energy transport mechanisms are investigated. The findings reveal that long-distance energy transportation can occur in the Ho 3+ sublattice owing to the energy migration capability of Ho 3+ and that Ho 3+ as a bridge ion can realize interparticle energy transfer for upconversion luminescence. Moreover, well-designed NaYbF 4 :40%Ho@NaYF 4 :10%Nd core-shell nanoparticles with multimode responsiveness can emit different colored lights under varying excitation wavelengths, which are demonstrated in high-level anticounterfeiting and information identification. Therefore, this work paves a new way to understand the functionality of the Ho 3+ bridge in energy transfer upconversion and offers strategies for broadening energy transfer pathways and finely manipulating photon upconversion.
All-optically controlled artificial synapses for neuromorphic vision offer unique advantages in simplifying circuit design and minimizing power consumption, meeting the application demands of the current artificial intelligence era. However, developing all-optically controlled devices that combine high performance and high reproducibility remains a significant challenge. In this work, we demonstrate an all-optically controlled artificial synapse based on ZnO and Cs 2 CoCl 4 single crystal connected structure, which integrates light information sensing and processing capabilities. Relying on the simple series-connected structure, as well as the positive photoconductance of ZnO and the negative photoconductance of Cs 2 CoCl 4 , the optically controlled bidirectional synaptic plasticity is realized under ultraviolet and visible light stimulation without additional voltage modulation in the all-optically controlled synapse. In addition, leveraging its ultraviolet-enhanced feature extraction and visible-suppression capabilities, the all-optically controlled synapse can act as denoising units in bioinformation preprocessing and weight-updating units in feature recognition. The proposed all-optically controlled synapses exhibit excellent information perception, low-level noise reduction, and high-level cognition functions for bioinformation recognition under complex light conditions. We believe that this work can provide structural-level insights and inspirations in the design and fabrication of all-optically controlled synapses to promote the application for efficient neuromorphic vision in the future.
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