## 2 Materials and Methods  
The glass samples of general composition, (50 - x - y) CeO\({}_{2}\)-35 TeO\({}_{2}\)-15 SrF\({}_{2}\)-xEu\({}_{2}\)O\({}_{3}\)-yTb\({}_{4}\)O\({}_{7}\), where x = 0, 0.2, 1, 2, 4 and y = 0, 0.2, 1, 4, were prepared by a conventional melt-quenching method. The starting materials, CeO\({}_{2}\) (Sigma Aldrich, Burlington, MA, USA, 99.998%), TeO\({}_{2}\) (Alfa Aesar, Ward Hill, MA, USA, 99.99%), SrF\({}_{2}\) (Alfa Aesar, 99.99%), Eu\({}_{2}\)O\({}_{3}\) (Alfa Aesar, 99.99%) and Tb\({}_{4}\)O\({}_{7}\) (Alfa Aesar, 99.998%), were weighed and mixed in a porcelain crucible. Then, the mix was placed in a corundum crucible and put into a preheated furnace at the temperature of 1000 \({}^{\circ}\)C for 45 min to melt the starting materials. Next, the melt was taken out of the furnace and poured onto a brass plate at room temperature. The resulting glass was annealed at 350 \({}^{\circ}\)C for 12 h to remove residual stress. Parts of the samples were ground into powder before measurements to ensure uniformity of the light scattering and produce comparable luminescence intensity output. The powder X-ray diffraction patterns in the 20 range 10-80\(\circ\) were measured in a linear PIXcel detector (PANalitycal, Almelo, The Netherlands) using Cu K\(\alpha\) radiation (\(\lambda\) = 1.54056 A). Raman scattering was measured using a [PERSON] (Wotton-under-Edge, UK) InVia Raman spectrometer equipped with a confocal DM 2500 Leica optical microscope, a thermoelectrically cooled CCD as a detector and an argon laser operating at 488 nm. IR spectra were measured with a Nicolet (Madison, WI, USA) iS50 FT-IR spectrometer using pellets of powdered glasses mixed with KBr. The spectral resolution of Raman and IR spectra was set to 2 cm\({}^{-1}\). The excitation and emission spectra, as well as the luminescence decay times, were recorded using the Edinburgh Instruments (Edinburgh, UK) FLS 1000 equipped with a Xenon lamp. The emission as a function of temperature was measured using Linkam (Surrey, UK) THMS 600 Heating/Freezing Stage (The McCRONE group, Westmont, IL, USA), a 375 nm laser diode as an excitation source and the Hamamatsu Photonic multichannel analyzer PMA-12 equipped with a BT-CCD linear image sensor (Hamamatsu Photonics K.K, Shizuoka, Japan). The quantum yield (QY) was measured using the Hamamatsu PMA-12 spectrophotometer equipped with an integrating sphere. The accuracy of measurement is estimated to be \(\pm\)2.5%. The J-O parameters were calculated using refractive index values \(n=1.835\) (taken from [24]) and integrated intensities of \({}^{5}\)D\({}_{0}\)\(\rightarrow\)\({}^{7}\)F\({}_{\text{J}}\) (J = 1, 2, 4 and 6) lines denoted as \(I_{0}\), using the following Equations (1) and (2) [25]:  
\[A_{0-I}=A_{0-1}\frac{I_{0}I_{01}\
u_{01}}{I_{01}\
u_{0J}} \tag{1}\]  
where \(\
u_{0J}\) are the wavenumbers, and \(A_{0-J}\) are the transition rates of 4/4/4 Eu\({}^{3+}\) transitions. \(A_{0-0}\) can be obtained from Equation (2)  
\[A_{0-1}=n^{3}(A_{0-1})_{vac} \tag{2}\]  
where \((A_{0-1})_{vac}\) is equal to 14.64 s\({}^{-1}\)[26]. Then, the \(\Omega_{\text{J}}\) parameters were calculated from Equation (3)  
\[A_{J-I^{\prime}}=\frac{64\tau^{4}v^{2}e^{2}}{3h}\cdot\frac{1}{4\pi\epsilon_{0}} \chi\Omega_{J}\cdot\left|\left\langle 4f^{N}SLJ\right\|U^{\lambda}\right\|4f^{N}S^{ \prime}L^{\prime}J^{\prime}\right\rangle\left|^{2} \tag{3}\]  
where the nonzero reduced matrix parameters <\(U^{\lambda}\)> equal to 0.0032, 0.0023 and 0.0002 for \(\lambda=2\), 4 and 6, respectively [27]; \(v\) is transition frequency; \(e\) is the electron charge; \(h\) is a Planck constant; \(\epsilon_{0}\) is a vacuum permittivity; and \(\chi\) is equal n(n\({}^{2}+2)^{2}/9\).