Herein　bulk　phenyl-　and　carbon-modified　graphitic　carbon　nitride　(PCCN)　powders　with　tunable　fluorescent　emission　from　green-color　to　yellow-color　were　prepared　by　copolymerization　of　2,4-diamino-6-phenyl-1,3,5-triazine　and　2,2,6-triaminopyrimidine.　The　corresponding　nanosheets　with　blue-color　to　green-color　fluorescence　were　obtained　by　the　oxidation　of　their　bulk　powders　in　sulfuric　or　nitric　acid　and　then　ultrasonic　exfoliation.　The　typical　PCCN0.6　nanosheets　not　only　displayed　strong　green-color　fluorescence　but　also　exhibited　photocatalytic　oxidase-like　activity,　which　can　catalyze　the　oxidation　of　substrates　3,3′,5,5′-tetramethylbenzidine　and　Amplex　UltraRed　by　O2　to　produce　blue-color　colorimetric　product　and　pink-color　fluorescent　product,　respectively.　By　taking　advantage　of　green-color　fluorescence　and　photocatalytic　activity　of　PCCN0.6　nanosheets,　a　prototype　for　high-level　anti-counterfeiting　application　was　demonstrated　by　using　the　mixture　of　PCCN0.6　nanosheets　and　Amplex　UltraRed　as　the　fluorescent　ink.　©　2021　Elsevier　B.V.