**1. Introduction**

Nanoparticles are the building blocks for many materials and contribute to the rapid growth of nanoscience [1]. There has been wide interest in silver nanoparticles (Ag NPs) due to their unique properties arising from shape, size and composition finding their applications in sensing devices, bio-labelling, catalyst, electronics, photonics, surface-enhanced Raman spectroscopy (SERS) and biomedicine, etc. [2–7]**.** For the applications of environmental friendly NPs in various fields, development of easy preparation methods using nontoxic and nonhazardous materials and methods is needed. Biosynthesis route has many advantages compared to other synthesis methods, as these routes do not use high temperature, pressure, energy and toxic elements. Recently, several groups reported on the synthesis of biocompatible Ag NPs using natural sources like fungi, yeast, bacteria [8–12] and plant extracts [13–16]. The properties of biosynthesized metal or bimetallic.

NPs are different from those synthesized from chemical methods and laser ablation methods [17, 18] because they are highly stable, nontoxic and biocompatible as the surfaces of the NPs are coated with biogenic surfactants. Biosynthesized metal NPs have biomedical applications like antimicrobial coatings (e.g.

antibacterial, antifungal, antiviral activity, antiparasite) [19–22], drug deliveries [23], medical imaging [24], anticancer NPs [25], medical diagnostics, sensors [26], catalytic degradation of organic pollutants to enhance membrane treatment processes [27] and also as optical limiters [28, 29] in the field of optics.

The *Raphanussativus* leaves belong to the Brassicaceae family, call it Radish and it is root vegetable. Derivatives and various components of *Raphanussativus* consist of 2- Hexen 1- al (leaf aldehyde) 3- hexane 1- ol (leaf alcohol) and n- isobutyraldehyde and isovaleraldehyde, sapogenin, methin, levon, phosphatase, histamines and spasmolytic components, lysine, polyphenolic, Sulphoraphene, vanillic acids and raphanin**,** those are having various medicine utilities. These bio-molecules consist in the extract are binding on the surface of nanoparticles and reduce the ions to NPs, additionally keeping stabilize the nanoparticles.

Lanthanide (Ln3+) complexes are of great interest due to their large Stoke shifts, long emission lifetimes, and narrow emission bandwidths. Metal-enhanced luminescence of rare-earth ions is of great interest because of their applications in laser materials, nano-photonics, LEDs, and biosensors [30]. Few groups investigated that enhancement or quenching of luminescence is depending on the concentration, shape, and size of metal nanoparticles based on the interaction of metal nanoparticles and luminescence centres [31, 32]. In the presence of metallic nanostructures, the field around the rare-earth ions can alter the emission and excitation [33, 34]. The literature reported that luminescence enhancement is because of energy transfer between Ln3+ complexes and metal NPs [35]. Quantum yields and lifetimes are influenced by changing the decay rate of radiative and nonradiative transitions [36]. Nevertheless, the process elaborated in Ln3+ ion luminescence with Ag NPS is not clear and hence, essential to address which is a promising and fascinating challenge.

Here, we have synthesized silver nanoparticles by using *Raphanussativus* leaf extract. The aim of the work is to discuss the origin of the effect of Ag NPs on enhancing and quenching the luminescence intensity of Ln3+ complexes and their nonlinear optical properties.
