In this paper the frequency up-conversion process based on the Lanthanide ions and the effect of their distribution on the output power is considered. First, the rate equations governing the energy level populations of each ion are constructed in such a way that it can be sensitive to its location. Then, the numerical solution of many coupled rate equations (with the number of ions existent in the medium) is obtained using a computer program. Computations show that the output power can have different discrete values depending on the ions locations. The number of these discrete values increases and their distance decreases with the medium size, respectively. At the macroscopic lengths, the output power in terms of the ion distributions takes a symmetric and continuous shape.