Synthesis of ZnO quantum dots and their agglomeration mechanisms along with emission spectra based on ageing time and temperature

The ZnO quantum dots（QDs） were synthesized with improved chemical solution method.The size of the ZnO QDs is exceedingly uniform with a diameter of approximately 4.8 nm,which are homogeneously dispersed in ethanol.The optical absorption edge shifts from 370 nm of bulk material to 359 nm of QD materials due to the quantum size effect,while the photoluminescence peak shifts from 375 nm to 387 nm with the increase of the density of ZnO QDs.The stability of ZnO QDs was studied with different dispersion degrees at 0？C and at room temperature of 25？C.The agglomeration mechanisms and their relationship with the emission spectra were uncovered for the first time.With the ageing of Zn O QDs,the agglomeration is aggravated and the surface defects increase,which leads to the defect emission.

Structural and Spectroscopic Characterizations of ZnO Quantum Dots Annealed at Different Temperatures

Here, we report the synthesis and characterizations of sol-gel derived zinc oxide （ZnO） quantum dots （QDs） using zinc acetate dihydrate （Zn（CH3COO）2.2H20） and lithium hydroxide monohydrate （LiOH.H20） as raw material. The as-prepared ZnO QDs was annealed at different temperature （400, 700, and 900 ℃） and the structural, optical properties were investigated by X-ray diffraction （XRD）, high resolution transmission electron microscopy （HRTEM）, UV-Vis and photoluminescence （PL） spectroscopy. The powder XRD patterns of the obtained samples showed the formation of single-phase wurtzite structure and the morphological changes have been observed with increasing annealing temperature. In the absorption spectra, the optical band gap of nanocrystalline ZnO QDs decreased from 3.18 to 3.11 eV and the particle size increased with increasing temperature. In the PL spectra, a broad green emission peak related to defect levels in the visible range of the spectra have been recorded.

Self-Assembled Al Nanostructure/ZnO Quantum Dot Heterostructures for High Responsivity and Fast UV Photodetector

Light confinement induced by spontaneous near-surface resonance is inherently determined by the location and geometry of metallic nanostructures(NSs),offering a facile and effective approach to break through the limitation of the light-mater interaction within the photoactive layers.Here,we demonstrate high-performance Al NS/ZnO quantum dots(Al/ZnO) heterostructure UV photodetectors with controllable morphologies of the self-assembled Al NSs.The Al/ZnO heterostructures exhibit a superior light utilization than the ZnO/Al heterostructures,and a strong morphological dependence of the Al NSs on the optical properties of the heterostructures.The inter-diffusion of Al atoms into ZnO matrixes is of a great benefit for the carrier transportation.Consequently,the optimal photocurrent of the Al/ZnO heterostructure photodetectors is significantly increased by 275 times to ~1.065 mA compared to that of the pristine ZnO device,and an outstanding photoresponsivity of 11.98 A W-1 is correspondingly achieved under 6.9 MW cm-2 UV light illumination at 10 V bias.In addition,a relatively fast response is similarly witnessed with the Al/ZnO devices,paving a path to fabricate the high-performance UV photodetectors for applications.

Tailoring Classical Conditioning Behavior in TiO_(2) Nanowires:ZnO QDs-Based Optoelectronic Memristors for Neuromorphic Hardware

Neuromorphic hardware equipped with associative learn-ing capabilities presents fascinating applications in the next generation of artificial intelligence.However,research into synaptic devices exhibiting complex associative learning behaviors is still nascent.Here,an optoelec-tronic memristor based on Ag/TiO_(2) Nanowires:ZnO Quantum dots/FTO was proposed and constructed to emulate the biological associative learning behaviors.Effective implementation of synaptic behaviors,including long and short-term plasticity,and learning-forgetting-relearning behaviors,were achieved in the device through the application of light and electrical stimuli.Leveraging the optoelectronic co-modulated characteristics,a simulation of neuromorphic computing was conducted,resulting in a handwriting digit recognition accuracy of 88.9%.Furthermore,a 3×7 memristor array was constructed,confirming its application in artificial visual memory.Most importantly,complex biological associative learning behaviors were emulated by mapping the light and electrical stimuli into conditioned and unconditioned stimuli,respectively.After training through associative pairs,reflexes could be triggered solely using light stimuli.Comprehen-sively,under specific optoelectronic signal applications,the four features of classical conditioning,namely acquisition,extinction,recovery,and generalization,were elegantly emulated.This work provides an optoelectronic memristor with associative behavior capabilities,offering a pathway for advancing brain-machine interfaces,autonomous robots,and machine self-learning in the future.

Influence of Mg Composition on Optical Properties of Exciton Confinement in Strained Wurtzite ZnO/Mg_x Zn_(1-x) O Cylindrical Quantum Dots

Based on the effective-mass approximation and variational approach, excitonic optical properties are investigated theoretically in strained wurtzite （WZ） ZnO/MgxZn1-xO cylindrical quantum dots （QDs） for four different Mg compositions： x = 0.08, 0.14, 0.25, and 0.33, with considering a three-dimensional carrier confinement in QDs and a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization. The ground-state exciton binding energy, the interband emission wavelength, and the radiative lifetime as functions of the QD structural parameters （height and radius） are calculated in detail The computations are performed in the case of finite band offset. Numerical results elucidate that Mg composition has of ZnO/MgxZn1-x 0 QDs. The ground-state exciton a significant influence on the exciton states and optical properties binding energy increases with increasing Mg composition and the increment tendency is more prominent for small height QDs. As Mg composition increases, the interband emission wavelength has a blue-shift if the dot height L 〈 3.5 nm, but the interband emission wavelength has a red-shift when L 〉 3.5 nm. Furthermore, the radiative lifetime increases rapidly with increasing Mg composition if the dot height L 〉 3 nm and the increment tendency is more prominent for large height QDs. The physical reason has been analyzed in depth.

Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/Mg_xZn_(1-x)O quantum dots

Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong bulk-in electric field （BEF） in strained wurtzite ZnO/Mgo.25Zno.750 quantum dots （QDs）, the optical properties of ionized donor-bound excitons （D^＋, X） are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of （D^＋, X） complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of （D^＋, X） complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth.