Abstract
High resolution, low temperature photoluminescence spectra of manganese‐doped willemite 
single crystals have been measured. "Hot" bands on the zero‐phonon lines of the 
excited state of 
on inequivalent sites are observed at low Mn concentration between 4 K and 29 K. Their appearance is attributed to vibronic (Ham) quenching of the first‐order spin‐orbit interaction in the 
excited state, by analogy with known properties of 
in 
and 
. At higher Mn concentration, additional lines appear which are assigned to Mn pair centers involving substitution on nearest neighbor Zn sites. Electron microprobe analysis shows that the segregation coefficient of Mn incorporation in the crystal increases as the Mn concentration in the melt increases. This is indicative of pairwise incorporation during growth, and consistent with the optical detection of Mn pairs in the crystals at higher Mn concentrations. The measured luminescence decay times depend on both Mn concentration and temperature of the crystals, due to thermally activated energy transfer between Mn centers.