The Fluorescence Behavior and Stability ‎of AgNPs Synthesized by Juglans Regia ‎Green Husk Aqueous Extract

   Particles with the size of 1-100 nm are known as nanoparticles (NPs). The widespread use of silver NPs (AgNPs) makes it familiar in different industries. They have unique properties as a result of their high surface to volume ratio, although aggregation of NPs interferes with their functions. This phenomenon has several side effects on the environment, the amount of which may depend on the stability of AgNPs. Stability of colloids depends on various agents, such as capping agents and environmental conditions, including pH and ionic strength. In this study, the effects of a variety of electrolytes, such as NaCl (10mM), NaNO3 (10 and 100mM), andCa (NO3)2 (10mM)at different values of pH were investigated on the aggregation of AgNPs synthesized using an aqueous extract of dried Juglans regia green husk. In NaNO3 10mM pH 9, NPs were more stable than in other media. Therefore, the special optical and electronic properties of AgNPs in such a medium as well as in water were investigated. The UV-visible extinction spectra of AgNPs in both water and NaNO3 (10 mM, pH 9.0) showed a surface plasmon resonance (SPR) at 445 nm as well as a broad peak at shorter wavelengths (255 nm). The fluorescence emission spectra of AgNPs at different excitation wavelengths in the range of 245-290 nm revealed emission peaks that were red-shifted in the range of 487-580 nm by the increase in the excitation wavelength. This behavior is attributed to the existence of a variety of emission centers with different energy levels.