We studied the effect on conversion efficiency of a CdS/CdTe solar cell by applying a wavelength conversion of a rare earth ion. Both photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the Sm-doped KMgF3 crystal were investigated. As a result, we found that both the divalent and the trivalent Sm ions coexist in the grown KMgF3 crystals. Also, all the PLE spectra below 500nm were effectively converted to PL spectra above 540 mn and the solar cell possessed a high spectral response. The quantum efficiency of Sm ions was estimated to be 0.84 from the comparison of the experimental curve with the calculated one for the increased spectral response below 500 nm. When a thin disc crystal of KMgF3:SM was placed on the top of CdS/CdTe solar cell as a precursor for wavelength conversion, both the maximum output power and the conversion efficiency increased by 5% as compared with the case of a pure KMgF3 crystal. (C) 2003 Elsevier B.V. All rights reserved.