An　anomalous　enhancement　of　fluorescence　of　carbon　dots　(CDs)　was　observed　via　lanthanum　(La)　doping.　La-doped　CDs　(La-CDs)　were　prepared　through　microwave　pyrolysis　within　4　min.　With　La3+　doping,　the　emission　band　shifted　from　blue　to　green　although　La3+　is　non-fluorescent.　The　quantum　yield　and　fluorescence　lifetime　improved　by　about　20%　and　35%,　respectively.　All　experiment　results　indicate　that　La3+　doping　is　an　effective　way　to　tune　fluorescence　and　improve　the　performance　of　CDs.　Another　unique　attribute　of　La-CDs　is　high　sensitivity　to　Fe3+.　The　La-CD-based　fluorescence　probe　was　established　and　used　for　sensitive　and　selective　detection　of　Fe3+　with　a　limit　of　detection　of　91　nmol/L.　The　proposed　fluorescence　probe　also　was　successfully　employed　to　visualize　intracellular　Fe3+　in　live　HeLa　cells　through　cell　imaging.　It　was　also　shown　that　yttrium　exhibited　the　same　fluorescence　enhancement　effect　as　La.　The　results　may　provide　a　new　route　for　preparing　CDs　with　special　properties.