**5. Conclusion**

The degradation of recalcitrant compounds using semiconductors doped with lanthanides, in aqueous media, is a promising area due to the increasing incidence of these compounds in water media due to the inefficiency of current processes in eliminating such molecules. Doping semiconductors with lanthanides has been an efficient strategy to generate defects in the surfaces of the materials. These defects act as active sites that capture the electrons and prevent recombination events or increase the density of hydroxyl groups and increase the amount of water molecules bound on the surface of photocatalytic materials. All these mechanisms increase the efficiency of the photodegradation processes. However, the excess of these dopants reduces the photocatalytic capacity of the semiconductor, possibly due to the excess of vacancies generated, which act as recombination centers instead of electrons scavenger.

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