Fig. 2

Energy diagrams for (a) BGG glass doped with Er³⁺ ions glass under excitation at the wavelength of 796 nm, 808 nm, 940 nm and 980 nm (b) BGG glass doped with Yb³⁺/Tm³⁺/Ho³⁺ ions glass under excitation at the wavelength of 796 nm, 808 nm (c) BGG glass doped with Yb³⁺/Tm³⁺/Ho³⁺ ions glass under excitation at the wavelength of 940 nm, 980 nm.