The present invention relates to nanosystems comprising metal atomic quantum clusters (AQCs) of at least two different sizes encapsulated in a cavity with an inner diameter less than or equal to 10 nm for the use thereof as luminescent nanosystems, particularly for the use thereof as fluorescent nanosystems; as well as the method for obtaining and detecting them. The invention also relates to the use of said luminescent nanosystems as a fluorescent probe, biomarker or contrasting agent.