Controlled growth of MPA-capped ZnS quantum dots through concentration-modulated single injection hydrothermal method

• Published in: Journal of crystal growth Vol. 644; p. 127834
• Main Authors: Sushma, M., Jai Kumar, B., Mahesh, H.M., Nagaraju, G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.10.2024
• Subjects: 3-mercaptopropionic acid; Bohr exciton radius; Quantum confinement; Quantum sensors; Urbach energy; ZnS quantum dots; Quantum confinement; 3-mercaptopropionic acid; Bohr exciton radius; Urbach energy; Quantum sensors; ZnS quantum dots
• ISSN: 0022-0248
• DOI: 10.1016/j.jcrysgro.2024.127834

•A CMSIH method for MPA-capped ZnS QDs improves growth efficiency, consistency, and reducing environmental impact.•The COOS method and temperature variation refine MPA, cation, and anion ratios, enhancing QD properties.•ZnS QDs’ unique blue emission suits them for LEDs, wearable electronics, and advanced quantum sensors.•Ultra-small ZnS QDs are synthesized for advanced quantum sensors, especially as radiation detectors. This study presents the controlled growth of 3-Mercaptopropionic acid (MPA)-capped ZnS quantum dots (QDs) using a concentration-modulated single injection hydrothermal method. Employing the Concentration optimization by optical spectra (COOS) method, we optimized the MPA:Zn:S ratios to investigate the influence of the capping agent, cation, and anion for exceptional properties suitable for optoelectronic and sensor applications. CMSIH operates as a single-step synthesis process, reducing processing time and complexity. This streamlined approach not only enhances efficiency but also minimizes the risk of contamination and ensures batch-to-batch consistency in QD production. Its moderate operating conditions, compared to other high-energy methods, also contribute to reduced energy consumption and environmental impact, aligning with sustainable manufacturing practices. Further, X-ray diffraction (XRD) confirmed the Zinc blend (cubic) phase of ZnS, and Fourier-transform infrared spectroscopy (FTIR) validated MPA capping. The QDs exhibited strong quantum confinement, causing a blue shift in absorption peaks compared to bulk ZnS. Higher MPA concentrations ranging from 0.02 M to 0.1 M induced a red shift in the absorption edge due to prolonged reaction times and strong cation binding by MPA. Variations in cation Zn and anion S ratios from 0.02 M to 0.1 M caused blue and red shifts in the absorption edge, respectively. For instance, Zn:S = 0.04:0.01 M increased cation concentrations, reducing QD size up to 0.67 nm, while enhanced anion concentrations Zn:S = 0.04:0.04 M enlarged the QDs size up to 2.35 nm. Remarkably, calculated QD sizes using Brus’ equation were smaller than the Bohr radius, even at an elevated temperature of 95 °C, indicating significant quantum confinement. Luminescence studies revealed reduced luminescence with higher MPA concentrations, increased luminescence intensity with higher cation Zn+ concentrations, and a red shift in the luminescence peak with higher anion S concentrations. As the temperature rises, there is an observable decrease in luminescence intensity. Furthermore, the investigation into the relationship between chemical composition and optical properties of MPA-capped ZnS QDs at elevated temperatures expands understanding of quantum confinement effects. The synthesised unique ultra small ZnS QDs can be used in advanced quantum sensors mainly as radiation detectors.