Encapsulation of 2-3-nm-sized ZnO quantum dots in a SiO2 matrix and observation of negative photoconductivity

Control of positive and negative photo- and thermal-responses in a single PbI2@CH3NH3PbI3 micro/nanowire-based device for real-time sensing, nonvolatile memory, and logic operation

CH3NH3PbI3 has shown great potential for photodetectors and photovoltaic devices due to its excellent positive response to visible light. However, its real-time response characteristics hinder its application in optical memory and logic operation; moreover, the presence of excessive PbI2 is a double-edged sword. Herein, we constructed a dual-terminal device using a single CH3NH3PbI3 micro/nanowire with two Ag electrodes, and then in situ introduced PbI2 quantum dots (QDs) as hole trap centres by thermal decomposition at 160 °C. An anomalous negative photoconductivity (NPC) effect for sub-bandgap light below the PbI2 bandgap is obtained. Importantly, an electrically erasable nonvolatile photomemory can be realized. Furthermore, the device also exhibits an abnormal positive thermal resistance (PTR)-related thermomemory effect, and the thermal-induced high-resistance state (HRS) can be erased by a large bias or an illumination of 365 nm super-bandgap UV light. Additionally, logical "OR" gate operations are achieved through a combination of 650 nm sub-bandgap light and a 70 °C temperature-induced HRS, as well as a large bias and 365 nm super-bandgap light-triggered low-resistance state. These effects are attributed to the excitation and injection of holes in QDs and structural defect traps. This multifunctional device, integrating real-time sensing, nonvolatile memory, and logical operation, holds significant potential for novel electronic and optoelectronic applications.

Nanotube Structure of AsPS4-xSex (x = 0, 1)

Single-wall nanotubes of isostructural AsPS4-xSex (x = 0, 1) are grown from solid-state reaction of stoichiometric amounts of the elements. The structure of AsPS4 was determined using single-crystal X-ray diffraction and refined in space group P 1 ¯ . The infinite, single-walled AsPS4 nanotubes have an outer diameter of ≈1.1 nm and are built of corner-sharing PS4 tetrahedra and AsS3 trigonal pyramids. Each nanotube is nearly hexagonal, but the ≈3.4 Å distance between S atoms on adjacent nanotubes allows them to easily slide past one another, resulting in the loss of long-range order. Substituting S with Se disrupted the crystallization of the nanotubes, resulting in amorphous products that precluded the determination of the structure for AsPS3Se. 31P solid-state NMR spectroscopy indicated a single unique tetrahedral P environment in AsPS4 and five different P environments all with different degrees of Se substitution in AsPS3Se. Optical absorption spectroscopy revealed an energy band gap of 2.7 to 2.4 eV for AsPS4 and AsPS3Se, respectively. Individual AsPS4 microfibers showed a bulk conductivity of 3.2 × 10-6 S/cm and a negative photoconductivity effect under the illumination of light (3.06 eV) in ambient conditions. Thus, intrinsic conductivity originates from hopping through empty trap states along the length of the AsPS4 nanotubes.

A facile covalent strategy for ultrafast negative photoconductance hybrid graphene/porphyrin-based photodetector

As a powerful complement to positive photoconductance (PPC), negative photoconductance (NPC) holds great potential for photodetector. However, the slow response of NPC relative to PPC devices limits their integration. Here, we propose a facile covalent strategy for an ultrafast NPC hybrid 2D photodetector. Our transistor-based graphene/porphyrin model device with a rise time of 0.2 ms and decay time of 0.3 ms has the fastest response time in the so far reported NPC hybrid photodetectors, which is attributed to efficient photogenerated charge transport and transfer. Both the photosensitive porphyrin with an electron-rich and large rigid structure and the built-in graphene frame with high carrier mobility are prone to the photogenerated charge transport. Especially, the intramolecular donor-acceptor system formed by graphene and porphyrin through covalent bonding promotes photoinduced charge transfer. This covalent strategy can be applied to other nanosystems for high-performance NPC hybrid photodetector.

Controllable Inverse Photoconductance in Semiconducting Nanowire Films

As a typical p-type semiconductor, tellurium (Te) has been widely studied for the construction of photodetectors. However, only the positive photoconductance of Te-based photodetectors based on the photoconductive effect has been observed in the reported literature. Herein, an unusual but interesting phenomenon, in that tellurium nanowires (NWs) behave with negative photoresponse to positive photoresponse under enlarged optical intensities from the UV to VIS-IR region is reported. According to the experiments and simulations, adsorbed oxygen on the surface of Te NWs plays a significant role in the abnormal photoresponse. The inverse photoconductance can be attributed to the competition between the photoconductive effect and the oxygen desorption effect. Moreover, the influence of the size and layers of Te NWs is also discussed. This inverse photoconductance phenomenon is further explored by introducing the Te-Au heterojunction system. Hot-electron injection at the Te-Au heterojunction interface induces a more obvious tendency to behave with a negative photoresponse. These findings will be beneficial for potential applications of Te-NW-based photodetectors.

CdTe@SiO2 signal reporters-based fluorescent immunosensor for quantitative detection of prostate specific antigen

In this paper, an immunosensor using CdTe@SiO₂ core-shell nanoparticles as labels was constructed for highly sensitive detection of prostate-specific antigen (PSA). In this approach, CdTe@SiO₂ core-shell nanoparticles were synthesized using the sol-gel method. The additional Cd ions and sulfur source in SiO₂ shell can greatly enhance the fluorescence intensity of CdTe nanocrystals. The reason is the formation of CdS-like cluster in SiO₂ shell, which reduced the quantum size effect. The obtained CdTe@SiO₂ nanoparticles also exhibited excellent biocompatibility, which was ideal for applying in biomarker detection. Furthermore, PSA capture antibodies functionalized magnetic Fe₃O₄ nanoparticles (Fe₃O₄-Ab₁) were utilized in the proposed immunosensor to capture and enrich the PSA. The captured PSA was then immuno-recognized by CdTe@SiO₂ labeled with PSA detection antibodies (CdTe@SiO_2-Ab₂) by forming the sandwich complex Fe₃O₄-Ab₁/PSA/Ab₂-CdTe@SiO₂. The construction of this immunosensor was confirmed by fluorescence spectroscopy. The proposed immunosensor showed a good linear relationship between the fluorescent intensity and the target PSA concentration ranging from 0.01 to 5 ng/mL, and a detection limit as low as 0.003 ng/mL was achieved. The sensor also exhibited good specificity to PSA. This highly sensitive and specific immunosensor has great potential to be used in other biological detection.

Decoration of reduced graphene oxide by gold nanoparticles: an enhanced negative photoconductivity

Photodetection in a visible light region is important in various applications, including computation, environmental monitoring, biological detection and industrial control. Due to this, research studies to develop photoconductive devices have great significance. We report a study on the photoconductivity of reduced graphene oxide (rGO)/gold nanoparticle (AuNP) nanocomposites, emphasizing the enhancement effect induced by AuNPs. rGO/AuNP photoelectric devices were prepared by spincoating rGO onto an AuNP-array-covered silicon substrate. Photoelectric responses under visible light illumination were measured and the results showed that the negative photoelectric responsivity of rGO was improved by 3 orders of magnitude due to AuNPs. The effects of AuNPs on negative photoconductivity (NPC) properties of rGO were investigated, and it was found that AuNPs affected NPC in three aspects: (1) AuNPs form discrete electrodes separated by nanoscale gaps which generated new conduction paths, and hence the conductivity of rGO was enhanced by 3 orders of magnitude; (2) localized surface plasmon resonance (LSPR) of AuNPs effectively enhances total light absorption of rGO; (3) photocurrent between AuNPs and rGO can weaken the NPC property of rGO. The low-cost and mass-producible rGO/AuNP nanocomposites demonstrate high photoelectric responsivity, which hold much promise for NPC devices.

Structural, optical and photoconductivity characteristics of pristine FeO·Fe2O3 and NTPI–FeO·Fe2O3 nanocomposite: aggregation induced emission enhancement of fluorescent organic nanoprobe of thiophene appended phenanthrimidazole derivative

In this manuscript we report the successful synthesis of pristine FeO·Fe₂O₃, 1-(naphthalen-1-yl)-2-(thiophen-2-yl)-1H-phenanthro[9,10-d]imidazole (NTPI), fluorescent organic nanoparticles (FONs) of NTPI and NTPI–FeO·Fe₂O₃ nanocomposite.

Enhancement of photoluminescence emission and anomalous photoconductivity properties of Fe3O4@SiO2 core–shell microspheres

We report the successful synthesis of both pristine Fe₃O₄ and the Fe₃O₄@SiO₂ core@shell structure. The Fe₃O₄@SiO₂ core@shell sample shows enhanced photoluminescence compared to pristine Fe₃O₄, while reduced and negative photoconductivity is observed in the same sample.

Arrays of nanorods composed of ZnO nanodots exhibiting enhanced UV emission and stability

A novel one-step coating and assembly approach for fabricating well-defined ZnO nanodot/SiO₂ nanorod arrays by hydrolysis-recrystallization growth from 1-D ZnO nanorods is described. The resultant composite nanorod arrays exhibit much enhanced UV emission efficiencies and excellent stability, and thus offer particular promise for application in UV emission devices operating in harsh environments.

In situ generation of well-dispersed ZnO quantum dots on electrospun silica nanotubes with high photocatalytic activity

The ZnO quantum dots-SiO(2) nanotubes (ZQDs-SNTs) nanocomposite was successfully fabricated by direct heat treatment of the electrospun zinc acetate/tetraethyl orthosilicate (TEOS)/polymer nanotubes (NTs). The results indicated that the ZnO quantum dots (ZQDs) with diameter about 3-5 nm were highly dispersed on the SiO(2) nanotubes (SNTs). And, there might be Zn-O-Si bonds between ZQDs and SiO(2) matrix, which formed interface states in the ZQDs-SNTs nanocomposite. The photocatalytic studies revealed that the ZQDs-SNTs nanocomposite exhibited high photocatalytic activity to degrade Rhodamine B (RB) under ultraviolet (UV) light irradiation, which might be ascribed to two reasons. The first one was the high dispersity of ZQDs; another one was the high separation efficiency of photogenerated electron-hole pairs due to the trap effect for photogenerated electrons of the interface states between ZQDs and SiO(2). During the photocatalytic reaction, the ZQDs-SNTs nanocomposite also exhibited high chemical stability in a wide range of pH values, which might be ascribed to the protective action of SiO(2) and the presence of Zn-O-Si bonds between ZQDs and SiO(2). Furthermore, the ZQDs-SNTs nanocomposites could be easily recycled because of their one-dimensional nanostructure property.

Development of a novel deltamethrin sensor based on molecularly imprinted silica nanospheres embedded CdTe quantum dots

A novel procedure for the determination of deltmethrin (DM) is reported. The water-soluble CdTe quantum dots (QDs) and highly fluorescent silica molecularly imprinted nanospheres embedded CdTe QDs (CdTe-SiO2-MIPs) were prepared and characterized by fluorescence spectroscopy, UV-vis spectroscopy, TEM and IR. The fluorescence nanosensor based CdTe-SiO2-MIPs is developed. The possible quenching mechanism is discussed by DM. Under optimal conditions, the relative fluorescence intensity of CdTe-SiO2-MIPs decreased with increasing DM by a Stern-Volmer type equation in the concentration range of 0.5-35.0 μg mL(-1), the corresponding detection limit is 0.16 μg mL(-1). The developed sensor based on CdTe-SiO2-MIPs was applied to determine DM in fruit and vegetable samples.

One-pot large-scale synthesis of robust ultrafine silica-hybridized CdTe quantum dots

A facile one-pot strategy for synthesis of silica-hybridized CdTe quantum dots (SiO(2)-h-CdTe QDs) in aqueous solution is presented, and subkilogram scale fluorescent SiO(2)-h-QDs can be readily produced in one batch. This approach also makes the tuning of emission wavelength and absorption bandgap of SiO(2)-h-QDs accessible for the first time. In the case of using MPA as ligand, the emission wavelength and absorption bandgap can be tuned in the range of 546-584 nm (the corresponding diameter of QDs increased from 2.0 to 3.2 nm) and 2.55-2.27 eV, respectively. The content of QDs in the resulting nanohybrids can also be readily adjusted in a wide range of 2-95 wt % by the feed ratio of QDs to silica precursors. The resulting SiO(2)-h-QDs are ultrafine with diameters 8-16 nm, and show excellent optical properties, high stability, low toxicity, and versatile surface functionality compared with the neat QDs. Various functional groups such as amino, epoxy, and hydroxyl can be readily introduced to the surface of SiO(2)-h-QDs by silane-coupling chemistry and surface-initiated polymerization. Our strategy opens up enormous opportunities to make full use of these robust fluorescent nanohybrids in various applications because of their facile availability, cost-effective productivity, and high stability.