A phosphor comprises a material having a formula of AMgD.sub.10O.sub.17:Eu.sup.2+,Mn.sup.2+, wherein A is at least an alkaline-earth metal selected from the group consisting of Ba, Sr, Ca, and combinations thereof; and D is at least a metal selected from the group consisting of Al, Ga, In, and combinations thereof; wherein Eu.sup.2+ ions are present in an amount from about 10 to about 50 atom percent of a combined quantity of A ions and europium ions, and Mn.sup.2+ ions are present in an amount from about 5 to about 30 atom percent of a combined quantity of magnesium ions and manganese ions. The phosphor is used alone or in conjunction with other phosphors to convert UV/blue radiation emitted by a source, such as an LED or a gas discharge device, to visible light.