A method for making a rare-earth oxyorthosilicate scintillator single crystal includes growing a single crystal from a melt of compounds including a rare-earth element (such as Lu), silicon and oxygen, a compound including a rare-earth activator (such as Ce), and a compound of a Group-7 element (such as Mn). The method further includes selecting an scintillation performance parameter (such as decay), and based on the scintillation performance parameter to be achieved, doping activator and Group-7 element at predetermined levels, or relative levels between the two, so as to achieve stable growth of the single-crystalline scintillator material from the melt.