This study presents a facile green synthesis of zinc aluminate nanophosphor by the microwave combustion method. Natural Piper nigrum seeds extract was used as a combustion agent. To study the effect of annealing temperature on structural, compositional, and optical properties of nano zinc aluminate, as-synthesized sample was further annealed at temperatures 700⁰C and 900⁰C. The structural and optical characterizations were carried out using XRD, UV-Vis DRS, FTIR, and PL spectroscopy. The XRD and FTIR confirmed the formation of nano zinc aluminate. The calculated average crystallite sizes were between 5-20 nm. The effective energy bandgap of prepared nano zinc aluminate was found to be 4.48 eV, larger than the bulk bandgap of zinc aluminate. Further, the effective band gap was increased with higher annealing temperatures. The PL spectra exhibited intense emission in the UV and blue region with weak emission in the red region.

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Carbon quantum dots are highly fluorescent, non-toxic, thermally stable, and water-soluble novel carbon nanomaterials. The dominance of quantum behavior has drawn scientists’ interest due to their good biocompatibility, low toxicity, high physicochemical and photochemical stability, and ease of synthesis. Carbon dots have shown applications in optoelectronics, photovoltaics, photocatalyst, biomedical such as biosensing, bioimaging, drug delivery, and detection for heavy metal ions in food and water samples. In this paper, we reported the microwave-assisted green synthesis of carbon dots using sweet lime as a carbon source and ethyl diamine as the surface passivating agent. The change in the optical and thermal properties are studied and analyzed with a change in the concentration of EDA in carbon dots. Synthesized samples are characterized by Dynamic Light Scattering and Zeta potential particle sizer to analyze the effect of EDA concentration on the distribution of particle size in the samples and change in surface charge of as-prepared carbon dots. The optical parameters are studied with UV- Visible absorption spectroscopy. Composition and molecular bonding are confirmed by Fourier Transform Infrared Spectroscopy. Thermal behavior and kinematics are studied by simultaneous Thermogravimetric Analyzer and Differential Scanning Calorimetry.