Some studies about the green and red light emitting structures in NaCl1−xBrx:Mn2+

• We study Mn2+ type nanostructures formed in mixed NaCl-NaBr single crystals.
• Red emission is associated to cubic type Mn2+ structures with small distortion.
• Green emission is due to Mn2+ structures with rombohedral symmetry.
• Mn2+ doped mixed sodium halides are good systems suitable for red-green emission.

In this work we present the results obtained from the luminescence spectra and X-ray diffraction as well as transmission electron microscopy, at room temperature on crystals of NaCl1−xNaBrx:MnCl2:0.3% (x=0.00, 0.05, 0.25, and 0.50). The results suggest the existence of structures between the crystal planes (1 1 1) and (2 0 0), which may be associated with different types of Mn2+ arrangements, such as dipole complexes, octahedral and rhombohedral structures as well as other possible nanostructures that include mixtures of bromine/chlorine ions. These are responsible for the emission spectra of “as grown” crystals consisting of maxima around 500 nm and 600 nm. The green emission has been usually attributed to rhombohedral/tetrahedral symmetry sites; the present results point out that this is due to Mn–Cl/Br nanostructures with rhombohedral structure. On the other hand when the crystals are thermally quenched from 500 °C to room temperature the structures previously detected present changes. Only a red band appears around 620 nm if the samples are later annealed at 80 °C.