Zero-phonon Mn²⁺ luminescence in natural grossular Ca₃Al₂(SiO₄)₃

A natural grossular garnet was found to have a luminescence spectrum with a narrow vibrational structure and short decay time that is unusual for minerals. We propose that such emission is generated by Mn²⁺ accompanied by defect F-centers which both enhance the transition probability and give rise to sensitivity to optical bleaching and reconstitution via irradiation. The elevated Mn concentration in comparison with other potential luminescent impurities was confirmed by LIBS analysis. Such interpretation contradicts the traditional opinion that Mn²⁺ centers in minerals are characterized only by broadband emission with very long decay times typical of d-d transitions.