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• The structure and mid-infrared luminescence in glass ceramics was investigated. • Oxyfluoride germanosilicate glass ceramics with varied Si/Ge ratio are prepared. • The influence of Si/Ge ratio on mid-infrared luminescence of samples were discussed. • Prepared glass ceramics possesses high emission cross section and gain coefficient. Changes in glass structure and crystallization behaviour from oxyfluoride silicate glass to oxyfluoride germanate glass were studied by modifying the ratio of Si/Ge in oxyfluoride germanosilicate glass ceramics, and transparent glass ceramic with low light scattering and efficient mid-infrared emissions were obtained. The NaYF 4 nanocrystals crystallization ability of oxyfluoride glass was decreased with the increase in Ge content, which can be attributed to the weakened oxide and fluoride phase separation in GeO 2 -rich glass. Upconversion and down-conversion emission spectra together with Ho3+: 5I 6 energy level fluorescent decay curves have been discussed for SiO 2 -rich glass ceramics and GeO 2 -rich glass ceramics, in which the fluoride crystallization induced the decrease of multi-phonon non-radiative decay rates plays the main role in the energy transfer processes. The influence of Si/Ge ratio on 2 μm and 3 μm fluorescent emissions in glasses and glass ceramics, and its link with glass network structural changes were discussed. The optimized Yb/Ho codoped oxyfluoride germanosilicate glass ceramic with low light scattering, high peak emission cross section(11.18 × 10−21cm2) and maximum gain coefficient (1.387 cm−1) at 2888 nm provides a potential application in the development of new 3 μm laser devices based on transparent oxyfluoride glass ceramic materials. [ABSTRACT FROM AUTHOR]