The photoluminescence (PL) and photoluminescence excitation (PLE) spectra are measured to investigate the luminescent properties (Figure 2 a,b). The excitation transitions are the spin-allowed 4A2!4T2 (longer wavelength) and 4A2!4T1 (shorter wavelength), the energy of which is strongly affected by the crystal field. In our case, no apparent changes in shape and position were observed in the excitation spectra.Thus, we assume that the strengths of the crystal fields in these systems are quite similar