A yellow phosphor having an increased activator concentration includes a host lattice comprising yttrium aluminum garnet (YAG) and an activator comprising cerium in the host lattice, where the cerium is present at a concentration of at least about 5 wt. % Ce. A method of making a yellow phosphor includes forming a reaction mixture comprising: a first precursor comprising cerium and oxygen; a second precursor comprising cerium and fluorine; a third precursor comprising yttrium; and a fourth precursor comprising aluminum. The reaction mixture is heated in a reducing environment at a temperature sufficient to form a yellow phosphor including a host lattice comprising yttrium aluminum garnet and an activator comprising cerium (Ce) incorporated in the host lattice.