Filling　the　cyan　gap　(470-500　nm)　in　white　light-emitting　diodes　(WLEDs)　is　crucial　for　full-spectrum　illumination.　However,　the　traditional　approach　of　adding　cyan　phosphor　to　red,　green,　and　blue　phosphors　can　lead　to　reabsorption　and　color　aberrations　due　to　spectral　overlap　and　varying　degradation　rates　among　the　mixed　phosphors.　Herein,　a　blue-cyan-emitting　phosphor　(lambda(em)　=　475　nm)　is　developed　through　Si4+-P5+　heterovalent　substitution　in　blue-violet-emitting　Rb3Y(PO4)(2):Eu2+　phosphor　(lambda(em)　=　425　nm),　which　can　serve　as　the　blue　component　in　WLEDs　to　fill　the　cyan　gap　without　adding　extra　phosphor.　Initially,　Eu2+　primarily　occupy　the　Rb2O(12)　sites　(426　nm)　in　Rb3Y(PO4)(2):Eu2+,　with　minimal　occupation　in　the　Rb1O(7)　sites　(456　nm)　and　YO6　sites　(522　nm).　The　Si4+-P5+　substitution　results　in　a　red-shift　of　the　Eu2+@Rb1　emission　peak　from　456　to　475　nm　and　the　preferred　occupation　of　the　Rb1　sites　by　Eu2+,　synergistically　achieving　the　blue-cyan　luminescence.　Employing　the　blue-cyan-emitting　phosphor　instead　of　the　blue-violet-emitting　phosphor　in　WLEDs　significantly　improves　the　color　rendering　index　from　90　to　97.2,　thus　enhancing　the　overall　color　reproduction　quality.　This　research　demonstrates　a　facile　composition　modification　method　to　modulate　the　properties　of　inorganic　luminescent　materials　and　provides　an　alternative　solution　for　full-spectrum　healthy　lighting.