Co-doping of Ag into Mn:ZnSe Quantum Dots: Giving Optical Filtering effect with Improved Monochromaticity

Dual Aliovalent Dopants Cu, Mn Engineered Eco-Friendly QDs for Ultra-Stable Anti-Counterfeiting

Doping in semiconductor quantum dots (QDs) using optically active dopants tailors their optical, electronic, and magnetic properties beyond what is achieved by controlling size, shape, and composition. Herein, we synergistically modulated the optical properties of eco-friendly ZnInSe2/ZnSe core/shell QDs by incorporating Cu-doping and Mn-alloying into their core and shell to investigate their use in anti-counterfeiting and information encryption. The engineered "Cu:ZnInSe2/Mn:ZnSe" core/shell QDs exhibit an intense bright orange photoluminescence (PL) emission centered at 606 nm, with better color purity than the undoped and individually doped core/shell QDs. The average PL lifetime is significantly extended to 201 ns, making it relevant for complex encryption and anti-counterfeiting. PL studies reveal that in Cu:ZnInSe2/Mn:ZnSe, the photophysical emission arises from the Cu state via radiative transition from the Mn 4T1 state. Integration of Cu:ZnInSe2/Mn:ZnSe core/shell QDs into poly(methyl methacrylate) (PMMA) serves as versatile smart concealed luminescent inks for both writing and printing patterns. The features of these printed patterns using Cu:ZnInSe2/Mn:ZnSe core/shell QDs persisted after 10 weeks of water-soaking and retained 70 % of PL emission intensity at 170 °C, demonstrating excellent thermal stability. This work provides an efficient approach to enhance both the emission and the stability of eco-friendly QDs via dopant engineering for fluorescence anti-counterfeiting applications.

Comparative Studies of Blue-Emitting Zinc Selenide Nanocrystals Doped with Ag, Cu, and Mg towards Medical Applications

Blue-emitting Ag(+)-, Cu(2+)-, and Mg(2+)-doped ZnSe nanoparticles (NPs) were successfully synthesized at 80 °C by the precipitation method by using mercaptopropionic acid (MPA) as a stabilizer. UV–visible and photoluminescence (PL) studies were applied to investigate their physicochemical properties. Their structural properties were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and transmission electron microscopy (TEM). The size of the ZnSe: X-capped MPA showed a strong relationship with dopant metals. The diameters of the Mg-doped ZnSe and the Cu-doped ZnSe were 22–24 nm, while the Ag-doped ZnSe was halved, at about 13 nm. The photoluminescence was within a wavelength range of 400–550 nm. In addition, the PL intensities, as well as the photoluminescence quantum yields, were in the order of the decreasing ionic radii of the dopant metals (ZnSe:Ag < ZnSe:Mg < ZnSe:Cu). Furthermore, through the interaction with lysine, the PL intensity of the ZnSe:X was changed. Interestingly, the capacity of the ZnSe:Mg for lysine was significantly higher than that of other dopant metals. Moreover, the toxicity of the ZnSe:Mg was relatively insignificant toward the hMSCs (about 80% cell viability at 320 ppm), compared to the transition-metal dopant. Therefore, the ZnSe:Mg material could have great potential for bioapplications.

Quaternary Alloy Quantum Dots as Fluorescence Probes for Total Acidity Detection of Paper-Based Relics

Traditionally, the acidity of paper-based relics was determined by an extraction method and using a pH meter. This method could not obtain the total acidity of the paper-based relics because it only detected the concentration of free protons in the aqueous soaking solution. To overcome this defect, a new method for determining the total acidity of paper-based relics has been established by using quaternary alloy quantum dots. The quantum dots, CdZnSeS, modified by p-Aminothiophenol (pATP) were prepared, and their composition and structure were characterized. The fluorescence behavior of prepared quantum dots with acidity was investigated. The following results were obtained. The fluorescence of CdZnSeS-pATP quantum dots could decrease with increases in acidity because pATP dissociated from the surfaces of the quantum dots due to protons or undissociated weak acids. Based on this feature, a method for determining the acidity of paper-based relics was constructed, and this method was used to evaluate the acidity of actual paper-based relics. Obviously, for a given paper sample, since both free protons and bound protons can be determined by this method, the acidity measured by this method is more reasonable than that by pH meter.

Rapid synthesis of hybrid methylammonium lead iodide perovskite quantum dots and rich MnI2 substitution favouring Pb-free warm white LED applications

We present a facile room temperature synthesis of CH₃NH₃Pb_1-x Mn _x I₃ perovskite quantum dots (PQDs) substituting manganese (Mn²⁺) at the lead (Pb²⁺) sites to minimize environmental pollution and make it commercially feasible. By varying the concentration of Mn²⁺ from 0 to 60%, the PQDs exhibit strong color tunability from red to orange color suggesting successful energy transfer due to Mn²⁺ inclusion. We observed a high external photoluminescence quantum yield (PLQY) of 98% for unsubstituted CH₃NH₃PbI₃ and >50% for up to 15% Mn²⁺ substituted PQDs. The average lifetime of PQDs was found to shorten with increasing Mn²⁺ replacement. We demonstrate a white LED prototype by employing the CH₃NH₃Pb_1-x Mn _x I₃ PQDs with green QDs on a blue LED chip. The CRI and CCT value varying from 92 to 80 and 5100 K to 2900 K, respectively, indicate the usability of the Mn²⁺ substituted PQDs as efficient warm white LEDs with a promising CRI and good stability.

Synthesis of Ag/Mn Co-Doped CdS/ZnS (Core/Shell) Nanocrystals with Controlled Dopant Concentration and Spatial Distribution and the Dynamics of Excitons and Energy Transfer between Co-Dopants

We report lightly Ag/Mn co-doped CdS/ZnS (core/shell) nanocrystals (NCs) as a model system for studying interactions between co-dopants and between NCs and dopants. The co-doped NCs were prepared with a varying average number of Ag dopant atoms per CdS core of the NC from zero to eight; at the same time, the depth profile of the Mn dopants in the ZnS shells was controlled to be either close to or far from the Ag dopants. The incorporation of an average of one to two Ag dopant atoms per NC increased the band-edge photoluminescence (PL); however, it was quenched at higher doping concentration. This alternation is attributed to change of the Ag ion occupancy from PL-enhancing interstitial sites to PL-quenching substitutional sites. Mn PL increased as the number of Ag atoms per NC increased up to approximately seven and then decreased. For NCs doped only with Ag ions, the Ag dopants in substitutional sites acted as PL-quenching hole traps. In Ag/Mn co-doped NCs, the Ag dopants acted as Dexter-type relay sites that enhanced the energy transfer from NC to Mn ions; this effect increased as the distance between Ag and Mn dopants decreased. This model study demonstrates that the simultaneous control of dopant concentrations and spatial distributions in co-doped semiconductor NCs enables sophisticated control of their optical properties.

Synthesis and electroluminescence of novel white fluorescence quantum dots based on a Zn–Ga–S host

White-light-emitting Ag, Mn: Zn–Ga–S/ZnS quantum dots (QDs) with a gratifying photoluminescence (PL) quantum yield (QY) of up to 90% were prepared, and shown to be ultra-stable, maintaining a high PL intensity at 300 °C or for 32 h of UV illumination.

Luminescent, low-toxic and stable gradient-alloyed Fe:ZnSe(S)@ZnSe(S) core:shell quantum dots as a sensitive fluorescent sensor for lead ions

In this paper, an aqueous-based approach is introduced for facile, fast, and green synthesis of gradient-alloyed Fe-doped ZnSe(S)@ZnSe(S) core:shell quantum dots (QDs) with intense and stable emission. Co-utilization of co-nucleation and growth doping strategies, along with systematic optimization of emission intensity, provide a well-controllable/general method to achieve internally doped QDs (d-dots) with intense emission. Results indicate that the alloyed ZnSe(S)@ZnSe(S) core:shell QDs have a gradient structure that consists of a Se-rich core and a S-rich shell. This gradient structure cannot only passivate the core d-dots by means of the wider band gap S-rich shell, but also minimizes the lattice mismatch between alloyed core-shell structures. Using this novel strategy and utilizing the wider band gap S-rich shell can obviously increase the cyan emission intensity and also drastically improve the emission stability against chemical and optical corrosion. Furthermore, the cytotoxicity experiments indicate that the obtained d-dots are nontoxic nanomaterials, and thus they can be considered as a promising alternative to conventional Cd-based QDs for fluorescent probes in biological fields. Finally, it is demonstrated that the present low-toxicity and gradient-alloyed core:shell d-dots can be used as sensitive chemical detectors for Pb²⁺ ions with excellent selectivity, small detection limit, and rapid response time.

Facile, one-pot and scalable synthesis of highly emissive aqueous-based Ag,Ni:ZnCdS/ZnS core/shell quantum dots with high chemical and optical stability

We report here on a one-pot, mild and low cost aqueous-based synthetic route for the preparation of colloidally stable and highly luminescent dual-doped Ag,Ni:ZnCdS/ZnS core/shell quantum dots (QDs). The pure dopant emission of the Ni-doped core/shell QDs was found to be highly affected by the presence of a second dopant ion (Ag⁺). Results showed that the PL emission intensity increases while its peak position experiences an obvious blue shift with an increase in the content of Ag⁺ ions. Regarding the optical observations, we provide a simple scheme for absorption-recombination processes of the carriers through impurity centers. To obtain optimum conditions with a better emission characteristic, we also study the effect of different reaction parameters, such as refluxing temperature, the pH of the core and shell solution, molar ratio of the dopant ions (Ni:(Zn+Cd) and Ag:(Zn+Cd)), and concentration of the core and shell precursors. Nonetheless, the most effective parameter is the presence of the ZnS shell in a suitable amount to eliminate surface trap states and enhance their emission intensity. It can also improve the bio-compatibility of the prepared QDs by restricting the Cd²⁺ toxic ions inside the core of the QDs. The present suggested route also revealed the remarkable optical and chemical stability of the colloidal QDs which establishes them as a decent kind of nano-scale structure for light emitting applications, especially in biological technologies. The suggested process also has the potential to be scaled-up while maintaining the emission characteristics and structural quality necessary for industrial applications in optoelectronic devices.

Surface Passivation of CdSe Quantum Dots in All Inorganic Amorphous Solid by Forming Cd1-xZnxSe Shell

CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd1-xZnxSe shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd1-xZnxSe core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials.

A highly efficient supramolecular photoswitch for singlet oxygen generation in water

A series of water-soluble supramolecular assemblies were constructed from dithienylethene-modified permethyl-β-cyclodextrins and porphyrin derivatives, accompanied by a high FRET efficiency, and could be applied in the control of singlet oxygen generation in a 1% ethanol aqueous solution upon irradiation of different wavelength light. These findings will provide a feasible and convenient way to construct a potential photodynamic therapy material.

Facile Synthesis of Cadmium-Free Zn-In-S:Ag/ZnS Nanocrystals for Bio-Imaging

High quality cadmium-free Zn-In-S:Ag doped-nanocrystals (d-NCs) were synthesized via a simple one-step noninjection route using silver nitrate, indium acetate, zinc acetate, oleylamine, S powder and 1-dodecanethiol as starting materials in an organic phase. The size and optical properties can be effectively tailored by controlling the reaction time, reaction temperature, Ag(+) dopant concentration, and the molar ratio of In to Zn. The photoluminescence wavelength of as-prepared Zn-In-S:Ag NCs covered a broad visible range from 458 nm to 603 nm. After being passivated by protective ZnS shell, the photoluminescence quantum yield (PLQY) of Zn-In-S:Ag(+) /ZnS was greatly improved to 43.5%. More importantly, the initial high PLQY of the obtained core/shell d-NCs in organic media can be preserved when being transferred into the aqueous media via ligand exchange. Finally, high quality Zn-In-S:Ag(+) /ZnS d-NCs in aqueous phase were applied as bio-imaging agents for identifying living KB cells.

An optical ratiometric temperature sensor based on dopant-dependent thermal equilibrium in dual-emitting Ag&Mn:ZnInS quantum dots

A novel optical sensor for ratiometric temperature detection is devised via Ag&Mn:ZnInS quantum dots (QDs). The temperature can be read via the PL ratios of Ag-related and Mn-related PL intensity.

Design and assembly of an aqueous red CdTe QD-LED: major factors to fabricate aqueous QD-LEDs

The aqueous red CdTe QD-LED with structure of ITO/PEDOT:PSS/PVK/CdTe QDs/ZnO/Al. Two major factors to fabricate an aqueous QD-LED successfully are adding wet agent to the QDs solution and removing the composite ions remaining in the QDs solution.

Efficient warm-white lighting using rare-earth-element-free fluorescent materials for saving energy, environment protection and human health

We explore an approach for efficient white light emission based on ZnSe:Mn nanoparticles without rare-earth and cadmium elements. This material opens up a new avenue for energy-saving, healthy, and environmentally benign lighting.