On the luminescence enhancement of Mn²⁺ by co-doping of Eu ²⁺ in ZnS:Mn,Eu

The photoluminescence and X-ray luminescence of ZnS:Mn, ZnS:Mn,Eu and ZnS:Eu were investigated and it was found that the luminescence intensity of Mn²⁺ in ZnS:Mn,Eu co-doped phosphors is highly dependent on the doping concentration of Eu²⁺. At the optimized Eu²⁺ concentration (0.2%), the photoluminescence of Mn²⁺ shows about a 5.5 times enhancement and its X-ray luminescence is enhanced by a factor of 2.5. Both wurtzite and zinc blend phases are present in the samples with wurtzite phase dominant. Co-doping of Eu²⁺ into ZnS:Mn does not change appreciably the ratio of the two phases or the Mn²⁺ emission luminescence lifetime; however, the doping of Eu²⁺ into ZnS:Mn does change the phonon activity. Furthermore, it was found that the defect-related blue emission of ZnS:Eu overlaps with the excitation bands of Mn²⁺ in ZnS:Mn and there is likely energy transfer from these defect states to Mn ²⁺ in ZnS:Mn,Eu. This energy transfer and the phonon modification are considered to be the two main reasons for the luminescence enhancement and the intensity dependence of Mn²⁺ emission on Eu²⁺ doping concentration in ZnS:Mn,Eu.