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1. Development of Quantum Dots Nanosensors for Heavy Metals Detection.

   Bailon-Ruiz, Sonia J; Cedeño-Mattei, Yarilyn (April 2024, Ceiba)

   This study demonstrates the potential application of polyethyleneimine (PEI)-modified quantum dots for sensing heavy metals, specifically copper ions, in aqueous matrices. Quantum dots were synthesized in aqueous phase, revealing a spherical morphology, a size of less than 5 nm, and a face-centered cubic crystalline structure. The presence of PEI on the quantum dots' surface significantly enhanced their photoluminescence within the range of 400 nm to 650 nm. To assess the sensor capabilities of PEI-capped quantum dots, two copper precursors (CuSO4 and CuNO3) were utilized at concentrations ranging from 0 ppm to 38 ppm. A systematic decrease in fluorescence intensity with increasing copper concentration was observed, establishing a quantitative relationship. These findings underscore the potential of PEI-modified quantum dots as efficient and selective sensors for copper ions. The concentration-dependent response in fluorescence intensity reflects the sensitivity of the system, suggesting promising applications in the field of heavy metal detection. 

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2. GaN Magic Angle Laser in a Merged Moiré Photonic Crystal

   https://doi.org/10.1021/acsphotonics.3c01064  

   Raun, Alexander; Tang, Haoning; Ni, Xueqi; Mazur, Eric; Hu, Evelyn L (September 2023, ACS Photonics)

   We demonstrate optically pumped blue lasing at room temperature in a merged moiré photonic crystal fabricated out of gallium nitride with embedded, fragmented quantum wells. Lasing occurs at two closely spaced wavelengths of 450 and 451 nm, matched to simulated flat bands induced by the moirésuperlattice. Both thresholds occur at 30 μJ/cm2. Light in−light out curves were taken at both room temperature and 77 K across different gain materials, including fragmented quantum wells, continuous quantum wells, and quantum dots. Lasing was observed only at room temperature in fragmented quantum well devices, suggesting the importance of gain material carrier dynamics in unconventional laser cavities like the moiré design explored. These insights and the experimental validation of moiré simulations in a previously unexplored III−V material indicate promise toward a new kind of efficient, tunable laser. 

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3. One-step Aqueous Synthesis of Zn-based Quantum Dots as Potential Generators of Reactive Oxygen Species

   https://doi.org/10.1557/adv.2019.27  

   Rivera, Julio A.; Bailón-Ruiz, Sonia J.; Perales-Perez, Oscar J. (January 2019, MRS Advances)

   Abstract The actual incorporation of dopant species into the ZnS Quantum Dots (QDs) host lattice will induce structural defects evidenced by a red shift in the corresponding exciton. The doping should create new intermediate energetic levels between the valence and conduction bands of the ZnS and affect the electron-hole recombination. These trap states would favour the energy transfer processes involved with the generation of cytotoxic radicals, so-called Reactive Oxygen Species, opening the possibility to apply these nanomaterials in cancer research. Any synthesis approach should consider the direct formation of the QDs in biocompatible medium. Accordingly, the present work addresses the microwave-assisted aqueous synthesis of pure and doped ZnS QDs. As-synthesized quantum dots were fully characterized on a structural, morphological and optical viewpoint. UV-Vis analyzes evidenced the excitonic peaks at approximately 310 nm, 314 nm and 315 nm for ZnS, Cu-ZnS and Mn-ZnS, respectively, Cu/Zn and Mn/Zn molar ratio was 0.05%. This indicates the actual incorporation of the dopant species into the host lattice. In addition, the Photoluminescence spectrum of non-doped ZnS nanoparticles showed a high emission peak that was red shifted when Mn 2+ or Cu 2+ were added during the synthesis process. The main emission peak of non-doped ZnS, Cu-doped ZnS and Mn-doped ZnS were observed at 438 nm, 487 nm and 521 nm, respectively. Forthcoming work will address the capacity of pure and Cu-, Mn-ZnS quantum dots to generate cytotoxic Reactive Oxygen Species for cancer treatment applications. 

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4. Ultrasmall HgTe Quantum Dots with Near-Unity Photoluminescent Quantum Yields in the Near and Shortwave Infrared

   https://doi.org/10.1021/acs.chemmater.4c01619  

   Coffey, Belle; Skytte, Elise; Ahmed, Tasnim; Vasileiadou, Eugenia S; Lin, Eric Yu; Sueh_Hua, Ash; Cook, Elijah; Tenney, Stephanie M; Sletten, Ellen M; Caram, Justin Ryan (August 2024, Chemistry of Materials)

   We demonstrate a low-temperature synthesis of ultrasmall (<2 nm) HgTe quantum dots (QDs) with superlative optical properties in the near and shortwave infrared. The tunable cold-injection synthesis produces HgTe QDs ranging from 1.7 to 2.3 nm in diameter, with photoluminescence maxima ranging from 900 to 1180 nm and a full-width at half-maximum of ∼100 nm (∼130 meV). The synthesized quantum dots display high photoluminescence quantum yields (PLQY) ranging from 80 to 95% based on both relative and absolute methods. Furthermore, samples retain their high PLQY (∼60%) in the solid state, allowing for first-of-their-kind photoluminescence imaging and blinking studies of HgTe QDs. The facile synthesis allows for the isolation of small, photostable HgTe quantum dots, which can provide valuable insight into the extremes of quantum confinement. 

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5. Strain Control of Magnetic Anisotropy in Yttrium Iron Garnet Films in a Composite Structure with Yttrium Aluminum Garnet Substrate

   https://doi.org/10.3390/jcs6070203  

   Liu, Ying; Zhou, Peng; Bidthanapally, Rao; Zhang, Jitao; Zhang, Wei; Page, Michael R.; Zhang, Tianjin; Srinivasan, Gopalan (July 2022, Journal of Composites Science)

   This report is on the nature of strain in thin films of yttrium iron garnet (YIG) on yttrium aluminum garnet (YAG) substrates due to film-substrate lattice mismatch and the resulting induced magnetic anisotropy. Films with thickness 55 nm to 380 nm were deposited on (100), (110), and (111) YAG substrates using pulsed laser deposition (PLD) techniques and characterized by structural and magnetic characterization techniques. The in-plane strain determined to be compressive using X-ray diffraction (XRD). It varied from −0.12% to −0.98% and increased in magnitude with increasing film thickness and was relatively large in films on (100) YAG. The out-of-plane strain was tensile and also increased with increasing film thickness. The estimated strain-induced magnetic anisotropy field, found from XRD data, was out of plane; its value increased with film thickness and ranged from 0.47 kOe to 3.96 kOe. Ferromagnetic resonance (FMR) measurements at 5 to 21 GHz also revealed the presence of a perpendicular magnetic anisotropy that decreased with increasing film thickness and its values were smaller than values obtained from XRD data. The PLD YIG films on YAG substrates exhibiting a perpendicular anisotropy field have the potential for use in self-biased sensors and high-frequency devices. 

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