Deep-red　light-emitting　diodes　(DR-LEDs,　＞660　nm)　with　high　color-purity　and　narrow-bandwidth　emission　are　promising　for　full-color　displays　and　solid-state　lighting　applications.　Currently,　the　DR-LEDs　are　mainly　based　on　conventional　emitters　such　as　organic　materials　and　heavy-metal　based　quantum　dots　(QDs)　and　perovskites.　However,　the　organic　materials　always　suffer　from　the　complicated　synthesis,　inferior　color　purity　with　full-width　at　half-maximum　(FWHM)　more　than　40　nm,　and　the　QDs　and　perovskites　still　suffer　from　serious　problems　related　to　toxicity.　Herein,　this　work　reports　the　synthesis　of　efficient　and　high　color-purity　deep-red　carbon　dots　(CDs)　with　a　record　narrow　FWHM　of　21　nm　and　a　high　quantum　yield　of　more　than　50%　from　readily　available　green　plants.　Moreover,　an　exciplex　host　is　further　established　using　a　polymer　and　small　molecular　blend,　which　has　been　shown　to　be　an　efficient　strategy　for　producing　high　color-purity　monochrome　emission　from　deep-red　CDs　via　Forster　energy　transfer　(FET).　The　deep-red　CD-LEDs　display　high　color-purity　with　Commission　Internationale　de　l＇Eclairage　(CIE)　coordinates　of　(0.692,　0.307).　To　the　best　of　the　knowledge,　this　is　the　first　report　of　high　color-purity　CD-LEDs　in　the　deep-red　region,　opening　the　door　for　the　application　of　CDs　in　the　development　of　high-resolution　light-emitting　display　technologies.