Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Applied Physics | en_US |
| dc.contributor.advisor | Hao, Jianhua (AP) | en_US |
| dc.creator | Zhao, Yifei | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14548 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Photoluminescence in smart nanocomposites and ferroelectric ultrathin films | en_US |
| dcterms.abstract | The exponential growth in information across diverse media drives an urgent need for multifunctional materials and devices beyond conventional electrical paradigms. Optical signal processing offers a promising route with contactless operations, parallel processing capabilities, high information bandwidth, and potential visualization of output signals. While “smart phosphors” with stimuli-responsive photoluminescence (PL) properties have seen widespread utilizations in optical information encryption and data storage, the dynamic aspect of PL variations and its implementation in optical information processing have not been fully harnessed. To bridge this gap, this thesis explores the construction of smart nanocomposites with PL-based neuromorphic behaviors using mixed-halide perovskite (MHPe) and macroporous Y₂O₃:Eu (MYE) smart nanocomposite. An all-optical physical reservoir computing is further developed based on MHPe@MYE smart phosphor, evidencing the potential of PL functions in classification of complex image datasets. After confirming the capability of PL functions in optical information processing, the down-scaling integration of PL into existing main-stream thin-film platforms is then explored. Ferroelectric (FE) HfO₂ has garnered significant research attention due to the exceptional nanoscale ferroelectricity and complementary-metal-oxide-semiconductor (CMOS) compatibility. Therefore, the thesis demonstrates the scaling-down incorporation of PL functions into ultrathin HfO₂ films through Er³⁺ doping with simultaneously improved FE endurance, potentially pathing the way towards multimodal neuromorphic devices at ultrathin levels. | en_US |
| dcterms.abstract | In the first part of the thesis, MHPe@MYE smart nanocomposites with porous structure are constructed by hard-templated sol-gel syntheses. It demonstrates progressively evolving PL properties variations upon light stimuli in the ultraviolet (UV) and blue region. The memristor-like PL variations with all-optical “Write” and “Read” processes are originated from the light-induced and dark-recoverable halogen migrations within MHPe@MYE. Density function theory (DFT) theoretical simulation reveals that a compositional adaptive halogen migration at the interface between MHPe and MYE plays a crucial role in these neuromorphic PL variations. Spectral investigations demonstrate rich neuromorphic properties that closely mimic biological synaptic behaviors, including paired-pulse facilitation (PPF), stimuli-dependent synaptic behaviors, and long-term memory (LTM). | en_US |
| dcterms.abstract | In the second section, the PL-based neuromorphic computing capabilities of MHPe@MYE are further evaluated by leveraging the non-linear and volatile PL variation features. Utilizing optical stimuli and PL-readouts as a physical reservoir, the system achieves discrimination of 4-bit binary sequences. Furthermore, it exhibits considerable potential for image recognition tasks, attaining an accuracy of 94.4% in classifying the Modified National Institute of Standards and Technology (MNIST) handwritten digits and UV fingerprints from Sokoto Coventry Fingerprint (SOCOFing) dataset. Such a PL-based physical reservoir concept is found broadly applicable to conventional “smart phosphor” systems such as persistent luminescence (PersL) phosphors, demonstrating the vast potential of PL functions in the emerging information science applications. | en_US |
| dcterms.abstract | The third part of the thesis focuses on the introduction of PL functions into FE HfO₂ to establish an ultrathin-film-level dual-mode platform. It is found the Er³⁺ dopant can not only introduce both UC and DC PL into HfO₂, but also simultaneously stabilize the metastable ferroelectricity in HfO₂. DFT theoretical investigation evidences the two-way doping effect of Er³⁺ to induce in-gap localized Er 4f-f transitions while anchoring charged oxygen vacancies (Vo) to prevent domain wall pinning and electrical breakdown during cyclic FE switching. The experimental growth of 7 a.t.% Er³⁺-doped HfO₂ (HErO) by pulsed-laser deposition (PLD) results in high-quality epitaxial thin film. Robust ferroelectricity can be obtained across a wide thickness range of 3 - 30 nm with modest remnant polarization of ~21 μC/cm². Notable endurance is observed to survive more than 10¹¹ switching cycles at 1M Hz without breakdown or obvious degradation. Concomitant with Er-stabilized ferroelectricity, the distinct Er³⁺ energy levels in HErO enable PL spanning both near-infrared (NIR, ~1550 nm, via DC) and visible regimes (520-650 nm, via UC) under 980 nm excitation. Such intrinsic PL integration of FE HfO₂ may render extended information freedom and process versatility for future dual-mode neuromorphic computing. | en_US |
| dcterms.extent | xxii, 155 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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