Kai-Kai Liu

Europium-decorated ZnO quantum dots as a fluorescent sensor for the detection of an anthrax biomarker

A hybrid nanostructure based on ZnO quantum dots (QDs) has been fabricated for ratiometric detection of Bacillus anthracis spores, where yellow-emitting ZnO QDs are employed as the internal reference and europium ions (Eu3+) are chelated on the surface of the ZnO QDs as the signal report unit. The Eu3+ exhibits enhanced red luminescence upon bonding with calcium dipicolinate (CaDPA), an important biomarker of Bacillus anthracis spores, while the fluorescence of the ZnO QDs will not be altered. Accordingly, increased CaDPA levels can lead to variation of the two fluorescence intensity ratios of the ZnO/Eu hybrid nanostructure. The time-dependent fluorescence response reveals that the reaction can be completed within 8 s, thus enabling the rapid detection of Bacillus anthracis spores. The detection limit for CaDPA is 3 nM, which is six orders of magnitude lower than an infectious dosage of Bacillus anthracis spores for human beings (60 μM). In addition, the sensor shows a remarkable selectivity for CaDPA over other aromatic ligands, amino acids and common cellular ions. The fast response speed as well as good sensitivity and selectivity means the ZnO/Eu nanostructure has great potential applications in clinical analysis.

Rewritable Painting Realized from Ambient-Sensitive Fluorescence of ZnO Nanoparticles

Paper, as one of the most important information carriers, has contributed to the development and transmission of human civilization greatly. Meanwhile, a serious problem of environmental sustainable development caused by the production and utilization of paper has been resulted to modern society. Therefore, a simple and green route is urgently demanded to realize rewritable painting on paper. Herein, a simple route to rewritable painting on copy paper has been demonstrated by using eco-friendly ZnO nanoparticles (NPs) as fluorescent ink, and vinegar and soda that are frequently used in kitchen as erasing and neutralizing agents. Words or patterns written using the ZnO NPs as ink can be erased by vinegar vapour within five seconds, and after a neutralizing process in the ambient of soda vapour, the paper can be used for writing again. It is worth noting that the resolution and precision of the patterns produced via the above route degrade little after ten rewriting cycles, and the quality of the patterns produced using the ZnO NPs as ink fades little after being storage for several months, which promises the versatile potential applications of the rewriting route proposed in this paper.

Fluorescence of ZnO/carbon mixture and application in acid rain detection

A ZnO and carbon nanoparticle (NP) mixture has been prepared. The fluorescence color of the mixture changes from yellow to blue when the pH value of the ambient is smaller than 5.5, which accords well with the pH standard value of acid rain (<5.6). This colorimetric change can be observed clearly by the naked eye, and thus the mixture can be employed as a probe to detect acid rain. The mechanism for the colorimetric change can be attributed to the fluorescence quenching of the ZnO NPs in acidic conditions. The results demonstrated in this paper provide a visual detection route for acid rain by the naked eye for the first time, and thus may be promising for the wide application of acid rain detection in the future.

Large-scale synthesis of ZnO nanoparticles and their application as phosphors in light-emitting devices

A simple one-pot route to large-scale synthesis of ZnO nanoparticles (NPs) has been demonstrated, and the ZnO NPs can be produced more than 34 grams in one synthesis process. The ZnO NPs show bright yellowish fluorescence under ultraviolet illumination with a quantum yield (QY) of 42%, which make them suitable for application as phosphors in light-emitting devices (LEDs). Yellowish LEDs have been fabricated by employing the ZnO NP powder as phosphors, and the luminous efficiency of the LEDs can reach 64.2 lm/W. Additionally, the fluorescence intensity of the phosphors shows little degradation when the ambient temperature reaches 100 °C, and the correlated color temperature of the LEDs remains constant when the driving current reaches 100 mA, indicating the good temperature and injection-current stability of the ZnO NP phosphors.

Advanced encryption based on fluorescence quenching of ZnO nanoparticles

Encryption is of vital importance in both military and civil fields. Although there have been a few attempts to encrypt information and produce anti-counterfeiting techniques employing functional materials, it is still urgently needed to develop advanced encryption routes that cannot be cracked easily. This paper presents a simple strategy for advanced encryption based on the fluorescence quenching of ZnO nanoparticles (NPs) by acid and copper ions. In this strategy, certain patterns are printed onto a ZnO NP pre-coated paper using a CuCl2 aqueous solution as an ink to produce an invisible latent image, which is only visible under ultraviolet (UV) irradiation. For encryption, the patterns can be perfectly concealed by exposure to vinegar vapour, due to the dissolution of the ZnO NPs in acidic conditions, and decryption can be performed via neutralization in an ambient soda vapour environment and subsequent uniform re-coating with ZnO NPs. An additional matrix of pixels with encoded grey levels acquired by tuning the dose of CuCl2 is demonstrated to further enhance the anti-counterfeiting capability. A 4 × 4 micron matrix with a total combination of 1.67 × 108 codes has been enciphered in the latent patterns for demonstration, and this is a huge barrier for counterfeiting. The results reported in this paper provide a simple strategy for advanced encryption, and may inspire versatile applications in the fields of information security and anti-counterfeiting.

Oleylamine-assisted and temperature-controlled synthesis of ZnO nanoparticles and their application in encryption

A temperature-controlled synthesis process for ZnO nanoparticles (NPs) with the assist of oleylamine (OAm) has been demonstrated, and the ZnO NPs show bright fluorescence under ultraviolet illumination. In this process, zinc nitrate was firstly converted to zinc nitrate hydroxide (Zn5(OH)8(NO3)2) sheets with the assist of OAm, then the Zn5(OH)8(NO3)2 was decomposed into fluorescent ZnO NPs by increasing the ambient temperature. Furthermore, information encryption has been realized based on this process. For encryption, the encrypted information cannot be observed, while the encrypted information appears when they are proceeded in the temperature of 120 °C for about one minute. The results shown in this work provide a controllable way for the synthesis of ZnO NPs by adjusting the reaction temperature, and this may inspire wide applications of ZnO in information encryption.

Towards efficient and stable multi-color carbon nanoparticle phosphors: synergy between inner polar groups and outer silica matrix

Nanocarbon as an eco-friendly and abundant material has strong multi-color fluorescence, which makes it a promising candidate for healthy lighting and display. However, the low fluorescence efficiency and poor stability of multi-color carbon nanoparticle (CNP) phosphors are main hurdles that hinder their applications. This work demonstrated efficient and stable multi-color CNP phosphors through synergy between inner polar groups and outer silica matrix. The polar groups in polyethylene glycol (PEG) 6,000 are favor of high fluorescence of the CNP phosphors, and the low melting point (64°C) of PEG 6,000 helps to improve the thermal stability of the phosphors, while the silica matrix provides protection to the phosphors. Based on this design, blue, green, yellow and red CNP phosphors with photoluminescence quantum yield of 53.1%, 47.4%, 43.8% and 42.3% have been achieved, all of which are the best values in ever reported multi-color CNP phosphors. Furthermore, the fluorescence of the CNP phosphors keeps almost unchanged at 100°C and degrades little in one month, indicating their good thermal tolerance and temporal stability. In addition, multicolor devices including white light-emitting devices (LEDs) have been realized by coating the CNP phosphors onto UV chips. The luminous efficiency, correlated color temperature, Commission Internationale de L’Eclairage and color rendering index of the white LED can reach 12 lm W−1, 6,107 K, (0.32, 0.33) and 89, respectively, indicating the potential applications of the CNP phosphors in lighting and display.摘要纳米碳作为一种资源丰富的环境友好型材料, 会产生明亮的多色荧光, 成为一种在健康照明与显示领域有前景的材料. 然而多色碳 纳米粒子荧光粉的荧光效率和稳定性仍然低于预期, 这极大地限制了碳纳米粒子的应用. 本工作通过内层极性官能团与外层二氧化硅的 协同作用, 制备了高效稳定的多色碳纳米颗粒荧光粉. 聚乙二醇6000中的官能团有利于碳纳米粒子的发光, 其较低的熔点(64°C)提升了碳 纳米粒子的热稳定性, 而外层的二氧化硅对荧光粉提供了保护作用. 基于这个设计, 制备出了量子效率为53.1%, 47.4%, 43.8%以及42.3%的 蓝光、绿光、黄光和红光碳纳米粒子荧光粉, 量子效率均为已报道的多色碳纳米粒子荧光粉的最高值. 所制备的碳纳米粒子荧光粉展现 了良好的热稳定性和时间稳定性, 其荧光在100°C和一个月后仍能保持不变. 将所制备的碳纳米粒子荧光粉涂覆到紫外芯片上, 实现了包 括白光在内的多色发光器件. 其中, 白光器件的流明效率为12 lm W−1, 色温, 色坐标和显色指数分别为6107 K, (0.32,0.33)和89, 表明碳纳米 粒子荧光粉在照明与显示领域有潜在的应用前景.

Multi-zinc oxide-cores@uni-barium sulfate-shell with improved photo-, thermal-, and ambient-stability: Non-equilibrium sorption fabrication and light-emitting diodes application

ZnO as an eco-friendly material shows bright luminescence under UV illumination when it is tailored into nanoscale size, which makes it a promising luminescent nanomaterial. However, the poor stability of ZnO hinders its applications drastically. In this work, multi-ZnO-cores@uni-BaSO4-shell (mZnO@uBaSO4) nanocomposite has been prepared through a non-equilibrium sorption process employing ZnO QDs as the seeds and BaSO4 as the valve. The mZnO@uBaSO4 nanocomposite shows improved photo-, thermal- and ambient-stability compare with bare ZnO QDs. The fluorescence efficiency of the mZnO@uBaSO4 nanocomposite decreases little even after 60u202fh of UV irradiation compare with ZnO QDs. The mZnO@uBaSO4 nanocomposite shows bright luminescence with little decrease even the ambient temperature up to 160u202f°C and the nanocomposite shows strong resistance to harsh environment. By coating the mZnO@uBaSO4 nanocomposite and commercial phosphors onto UV-chip, light-emitting diode (LED) with correlated color temperature, Commission Internationale de LEclairage coordinate, color rendering index and luminous efficiency of 6109u202fK, (0.32, 0.33), 85 and 47.33u202flm/W have been realized, and this will make a great step towards eco-friendly UV-pumped LEDs.

Silica encapsulated ZnO quantum dot-phosphor nanocomposites: Sol-gel preparation and white light-emitting device application

ZnO quantum dots (QDs) as an eco-friendly and low-cost material has bright fluorescence, which makes it promising material for healthy lighting and displaying. However, the low fluorescence efficiency and poor stability of ZnO QDs impede their applications in lighting application. In this work, silica encapsulated ZnO QD-phosphors nanocomposites (ZSPN) have been prepared through a sol-gel synthesis process, where yellow-emitting ZnO QDs and blue-emitting BaMgAl10O17:Eu2+ are employed as the luminescence cores and silica as link between two luminescence materials. Tunable photoluminescence of ZSPN and the white light emission have been achieved through changing mass ratio of both of ZnO QDs and commercial phosphors. The PLQY of the ZSPN can reach 63.7% and they can maintain high luminous intensity even the ambient temperature up to 110 °C and after 35 h of UV irradiation. In addition, they can keep stable for 40 days. By coating the ZSPN phosphors onto a ultraviolet chip, WLEDs with luminous efficiency of 73.6 lm/W and the color coordinate, correlated color temperature, and color rendering index can reach (0.32, 0.34), 5580 K, and 87, respectively, indicating the bright prospect of the ZSPN phosphors used in healthy lighting.