We have studied the semiconductor-metal transition (SC-MT) by following the optical absorption due to 4f6 → 4f5 5d(E1, E2) characterizing Sm2+ ions both in the semiconducting and metallic phases of SmS and Sm1-xLnxS films. For Ln = Yb, the El and E2 transitions are well preserved for 0 ⩽ x < 1 showing the stability of Sm2+ and the absence of a SC-MT. For Ln = Tm, the definition of E1 and E2 disappear as x increases from 0 to 0.30 resulting in a broad maximum near 1 eV which resembles that of the metallic SmS film