A luminescent material can be formed by a process using a vacancy-filling agent that includes vacancy-filling atoms. In an embodiment, the process can include forming a mixture of a constituent corresponding to the luminescent material and the vacancy-filling agent. The process can further include forming the luminescent material from the mixture, wherein the luminescent material includes at least some of the vacancy-filling atoms from the vacancy-filling agent. In another embodiment, the process can include melting a constituent corresponding to the luminescent material to form a melt and adding a vacancy-filling agent into the melt. The process can also include forming the luminescent material from the melt, wherein the luminescent material includes at least some of the vacancy-filling atoms from the vacancy-filling agent. The luminescent material may have one or more improved performance properties as compared to a corresponding base material of the luminescent material.