The emission band of Sr(2)Si(5)N(8):Eu(2+) phosphors consists of two peaks originating from two different crystallographic sites for Eu(2+) activators in the Sr(2)Si(5)N(8) structure. The two-peak emission behavior is closely related to the energy transfer between activators at those sites. A rate-equation model involving the crystallographic information of the host was used to quantify the time-resolved photoluminescence spectra and to systematically analyze the energy transfer behavior.