Ultraviolet and visible upconversion emissions under infrared excitation have been obtained and compared in Nd3+-doped oxyfluoride glasses and glass ceramics prepared by different methods. The mechanisms involved in such processes have been analyzed. A spectroscopy study comparing absorption and upconversion excitation spectra has been carried out in order to discern in each case the mechanism involved in the origin of the upconversion emissions, i.e., two- or three-photon involved excited state absorption or energy transfer processes. The shape of the absorption and emission spectra and the relative upconversion efficiencies have been compared and explained taking into account the final distribution of the luminescent ions in the glassy and nanocrystalline phases.
