[en] Highlights: • Mathematical formulation of T_m_a_x–T_s_t_o_p method for LM-OSL is described. • The theory is validated experimentally on α-Al_2O_3:C. • The photoionization cross-section of OSL components of α-Al_2O_3:C are evaluated. - Abstract: A mathematical formulation and its experimental validation on α-Al_2O_3:C for evaluating the number of OSL components has been described. The method consists of various partial bleaching steps of LM-OSL curve and as a result, the peak position (T_m_a_x) of the resultant curve shifts if the system contains multiple components. However, for single component system the peak position of the resultant curve doesn’t change on partial bleaching for a phosphor obeying first order kinetics. The method has been theoretically formulated for single and multiple component system with different order of kinetics and validated experimentally on the commercial α-Al_2O_3:C OSL phosphor. The slope of the curve between shift in T_m_a_x and bleaching time gives the number of the OSL components and measure of their closeness in terms of photoionization cross-section. Based on this result, the photoionization cross-section of the two embedded peaks in the LM-OSL curve of α-Al_2O_3:C were found to be 1.51 × 10"−"1"8 cm"2 and 5.02 × 10"−"1"9 cm"2 using CW-OSL and NL-OSL method.