Enhancement of Mn red emission in CaGa2S4 compounds by co-doping rare-earth elements

When certain trivalent rare-earth ions (Ln's) are co-doped in CaGa₂S₄:Mn²⁺ as sensitizers, the Mn red emission of the compound is strikingly enhanced. In this work, efficiency of each lanthanide is studied. The best efficiencies are achieved with La³⁺-, Pr³⁺-, and Tb³⁺- co-doped compounds, for each of which the effects of concentrations of the co-doped ions on the Mn²⁺ emission are investigated. The energy-transfer mechanisms and the location of electronic energy levels of both the trivalent and the divalent lanthanides in the energy band gap of the host material are discussed. Depending on Ln's, charge transfer or cross-relaxation should be taken into account.