The role of phonons in the luminescence characteristics of SICLOF oxyfluoride glass and glass-ceramic fibers doped with Er³⁺/Yb³⁺

Recently developed SICLOF oxyfluoride glass and glass-ceramic fibers doped with Er³⁺/Yb³⁺ have been prepared for fiber applications and optically characterized. The luminescence efficiency of glass-ceramic fiber appeared to be two times higher than that for glass fiber. An interesting dependence of the luminescence intensity around 1530 nm on temperature has been observed as the temperature was altered in the range of 5–350 K. For glass-ceramic fibers this dependence was different from that for glass fibers. The difference has been interpreted with use of kinetic equations and values of maximum phonon energies (ħω_max) different for glass-ceramic and glass fibers. The obtained fittings indicate that during thermal treatment the ħω_max value decreases by 40–50 cm⁻¹. We also estimate how does such a change affect the luminescence efficiency and find that the phonon energy reduction can be responsible for at the most 28% of the luminescence efficiency improvement.