## 1 Introduction  
Nowadays, the technology of novel nanocomposite glasses containing noble metal nanoparticles (NPs) is extensively investigated, due to their potential applications in photonics, optoelectronics, and biological sensing devices [1; 2; 3; 4; 5]. It is related to the unique optical properties of such materials, and in particular, to surface plasmon resonance (SPR), which is caused by interactions between external electromagnetic radiation and the free electrons in the conduction band of metallic nanoparticles. If this phenomenon occurs in the vicinity of rare-earth (RE) ions, the luminescence signal can be amplified or quenched by a strong electric field induced by the plasmonic effect [6]. Among different rare-earths, Eu\({}^{3+}\) is a useful element in the analysis of luminescent properties of glass embedded Ag\({}^{0}\) NPs, due to the overlapping of its energy structure with the SPR band of silver nanoparticles. Moreover, europium embedded in low phonon glasses is characterized by a high emission efficiency in the visible range as a result of wide energy gap (approx. \(\Delta\)E = 12,000 cm\({}^{-1}\)) between the \({}^{5}\)D\({}_{0}\) emitting state and the \({}^{7}\)F\({}_{\text{J}}\) ground multiplet [7; 8]. The advantage of the Eu\({}^{3+}\) ion is also its common use as a spectroscopic probe of the site symmetry in different host matrices [9; 10]. The main approach relies on the analysis of the intensity ratio of electrical-dipole (ED: \({}^{5}\)D\({}_{0}\)\(\rightarrow\)\({}^{7}\)F\({}_{2}\)) to magnetic-dipole (MD: \({}^{5}\)D\({}_{0}\)\(\rightarrow\)\({}^{7}\)F\({}_{1}\)) transitions, which determines the asymmetry of the ligand environment and the covalency of metal-ligand bond [11; 12]. Enhancement of the Eu\({}^{3+}\) ion luminescence was reported for the first time by [PERSON] et al., who demonstrated, in borosilicate glass, an increase of almost 6 times at the wavelength of 612 nm under 312 nm laser excitation induced by Surface Plasmon Resonance (SPR) [13]. According to [PERSON] et al. an enhancement at 700% at 615 nm of germanate glasses containing silver NPs and Eu\({}^{3+}\) ions has been obtained, upon 3 h annealing [14]. Possible energy transfer mechanisms of amplifying or reducing the emission of RE ions as a result of metal nanoparticles interactions were widely described by [PERSON] and [PERSON] [15]. The efficiency of the interaction strongly depends on the size, geometry, the refractive index of the dielectric host, and the distribution of metallic nanoparticles [16; 17]. A lot remains to be done to clarify the NP formation process. In fact, conventional techniques of glass nanocomposite fabrication, such as ion-implantation [18], ion exchange [19], laser or X-ray beam irradiation [20], phase vapor deposition [21], and long-time heat treatment in reducing atmosphere, are quite complex due to multistep processing. The possible methods for fabricating silver nanoparticles in glasses were recently described by [PERSON], et al. [22]. Among the various techniques used for the preparation of nanocomposite glasses containing metal nanoparticles, sol-gel is one of the most popular and cheapest methods [23; 24]. Another important technique is the melt-quenching process with the presence of selective reducing agents (Sb\({}_{2}\)O\({}_{3}\), Bi\({}_{2}\)O\({}_{3}\), TeO\({}_{2}\) etc. ), followed by controlled heat-treatment of the precursor glass [25; 26]. In situ generation of silver nanoparticles in antimony-borate (KBS) glass nanocomposites have been widely discussed by [PERSON] and [PERSON] [27]. They suggested that in KBS glass, the Sb\({}_{2}\)O\({}_{3}\) plays the role of a mild reducing agent. It enables in-situ reduction of Ag\({}^{+}\) to Ag\({}^{0}\) in a single-step during the melting process, thereby providing a simple, low-cost method for the preparation of bulk photonic materials. A similar effect was analyzed by [PERSON], et al. in tellurite glass doped with erbium and silver ions [28].