ESR investigation of the enhancement of the Mn-related red photoluminescence in CaGa2S4 single crystals by rare earth element codoping

• We investigate the mechanism of the enhancing effect of some of REEs on the Mn red emission in Ca thiogallates.
• We measure ESR from 4.2 K to room temperature using single crystals of CaGa2S4 doped with both Mn and one of Ce, La and Yb.
• New ESR signals assigned to Mn2+ emerge by codoping with La or Ce (effective for enhancement) but not with Yb (no effect).
• Simulation of the angular dependent ESR signals shows that the enhancement is due to Mn ions replacing the Ga sites.
• It is shown that the codoping of Ce or La ions makes the occupation of Mn change from the Ca site to the Ga one.

The ternary compound CaGa2S4 doped with Mn exhibits a weak red luminescence which can be strongly enhanced by simultaneous doping with one of some rare earth elements. To clarify this enhancement effect, ESR experiments are carried out on two kinds of single crystals of CaGa2S4; Mn singly doped one and codoped one with La, Ce or Yb. The individual line shapes of the Mn2+ related ESR spectra of the Mn singly doped samples drastically change when codoped with La or Ce which is effective for the enhancement but little with Yb which has no effect. The results of analyzing the ESR data through the calculation of the effective spin Hamiltonian along with studies on photoluminescence spectra strongly suggest that Mn atoms at Ga sites play a main role of the enhancement of the Mn red emission.