## 1 Introduction  
Erbium-doped glasses are of crucial importance due to the generation of light at 1520-1570 nm, which corresponds to the intra-4f transition of Er\({}^{3+}\) from \({}^{4}\)I\({}_{13/2}\) to \({}^{4}\)I\({}_{15/2}\)[1]. There has been a constant need for improving the performance of such glasses, which could be achieved by developing new glass materials. Oxide glasses are known to be promising hosts for obtaining efficient luminescence from rare-earth (RE) ions [2]. Especially, Er\({}^{3+}\) doped phosphate glasses have been intensively studied for many years, as they are easy to process and they also possess good thermal stability and excellent optical characteristics, such as high transparency in the UV-Visible-Near Infrared (UV-Vis-NIR)region [3]. Additionally, they can incorporate a high amount of Er\({}^{3+}\) ions (as opposed to silicate glasses) without Er-Er clustering. It is well known that the local environment around the RE ions has a significant impact on the optical and spectroscopic properties of glasses [4]. In our recent study [5], we investigated the changes in the thermal, structural and luminescence properties of Er\({}^{3+}\) doped phosphate glasses induced by the addition of Al\({}_{2}\)O\({}_{3}\), TiO\({}_{2}\) and ZnO in low amount (1.5 mol %). We found that the addition of Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) has only a slight impact on the density, glass structure and spectroscopic (absorption and emission) properties of the glasses whereas the addition of ZnO increases the intensity of the emission at 1540 nm probably due to the depolymerization of the phosphate network. Therefore, we report here new findings on the preparation of the Er\({}^{3+}\) doped phosphate glasses with larger amount of ZnO to confirm the role of Zn in the glass network and, more importantly, its impact on the site of Er\({}^{3+}\) ions. Er\({}^{3+}\) doped glasses could find applications in telecommunications, LIDAR (Light Detection and Ranging), spectroscopy and bioimaging, just to cite a few. Recently, such materials were also found to be useful for optical inter-satellite links and other applications, such as amplifiers for highly distributed data networks and broadband super luminescent sources for fiber gyroscopes [6]. It was found that rare-earth doped fibers are more sensitive to irradiation than undoped optical fibers due to the formation of defects or color centers in the glass matrix, which lead to changes in the spectroscopic properties of the glasses and in the fiber losses [7]. The factors affecting the radiation-induced loss on doped fibers are: (i) the type of ionizing radiation; (ii) total absorbed dose; (iii) dose rate; (iv) rare-earth dopant concentrations; and (v) the fabrication parameters as reported in [8]. Therefore, when developing new Er\({}^{3+}\) doped glasses, the radiation effect in these glasses should be investigated in order to develop new radiation-resistant fibers suitable for space applications and nuclear environments. Our group in the National Institute for Laser, Plasma and Radiation Physics (Romania) has been running for several years, tests of ionizing radiation effects on optoelectronic materials components and device, optical fibers and optical fiber sensors, especially under gamma-ray, proton, electron beam, neutron, alpha particles irradiation, which are of interest for space applications or the operation of nuclear installations (nuclear power plants, nuclear waste repositories). Radiation hardening tests are of interest in relation to specific space missions, as ionizing radiation originating outside of Earth's atmosphere is constituted by 87% of protons, 12% of alpha particles and 1% of heavy elements. Recently, we reported, for the first time, a comprehensive study on alpha particle irradiation effects on four mid-IR materials [9] and gamma-ray-induced changes in Bi/Er co-doped optical fibers [10].