Origins of Efficient Multiemission Luminescence in Carbon Dots

Abstract

Although several groups have synthesized dual-emission carbon dots (D-CDs) and paid more attention to their emission centers in recent years, the luminescence mechanism of D-CDs is still unclear. Here, we synthesized multiemission CDs via the one-pot hydrothermal method. The prepared CDs exhibit three fluorescence (FL) emissions (370, 425, and 505 nm) under one-wavelength excitation of 320 nm. In addition, various emission origins dominate the unique multiemission property, which is illuminated by means of the radiation decay process, CD internal graphite domains, and abundant functional group characterization. The characterization results fully indicate that there are three energy states: band gap state (carbon-core state), surface defect state, and molecular state. In addition, the peculiar concentration-dependent and polarity-modulated properties further support the explanation of CD multienergy states. Strikingly, the CD FL quantum yield is up to 50.68%. As CDs can show bright green FL excited over 400 nm, the color of concentrated CD solution incredibly turns from maroon to green in visible light observed from different angles. Our findings mainly account for this luminescence mechanism of CDs. This work utilizes time-resolved emission spectra for the first time to distinguish and identify multiemission origins, which would provide scientific inspiration for finding effective ways to regulate or control these luminescence processes.

Nitrogen-doped fluorescence carbon dots as multi-mechanism detection for iodide and curcumin in biological and food samples

“…3 A depicted the UV–vis absorption of NCDs (blank line), an obvious and characteristic absorption peak at 287 nm was observed, which was ascribed to the typical absorption of π-π* transition of C=C [ 28 , 32 ]. There was also a weak absorption band from 300 nm to 400 nm which might be attributed to the n-π* transition of C=O bond [ 36 , 37 , 39 , 40 ]. Meanwhile, the maximum emission wavelength (blue line) of NCDs was located at 537 nm with the excitation wavelength (red line) at 460 nm.…”

“…3 B), which was a typical excitation-dependent fluorescence phenomenon. The fluorescence tunability of as-prepared NCDs is presumably due to the inhomogeneity of the particle sizes and the plenteous emissive traps of surface states formed by the hydroxyl, carboxyl and aminol functional groups [ 36 , 37 , 39 , 40 ]. The fluorescence quantum yield of as-fabricated NCDs at room temperature was measured to be 10.5% using quinine sulfate (QY = 54%, 0.1 M H 2 SO 4 ) as reference.…”

“…Based on the outstanding optical merits of NCDs in complex environments and the ample functional groups in the structure of NCDs, we further explored the applications in fluorescence sensors. Numerous metal ions could significantly quench the fluorescence of CDs due to the powerful affinity or fast electron transfer [ [28] , [29] , [30] , [31] , 36 , 37 , [39] , [40] , [41] , [42] , [43] ], and the CDs-metal ion complex emitted weak fluorescence, which provided a basis for the construction of fluorescence-enhanced sensor. Thus, we investigated the selectivity of as-prepared NCDs toward 18 metal ions including Na + , K + , Ca 2+ , Mg 2+ , Ba 2+ , Cr 3+ , Hg 2+ , Co 2+ , Cd 2+ , Mn 2+ , Cu 2+ , Zn 2+ , Fe 3+ , Al 3+ , Pb 2+ , La 3+ , Ni 2+ , and Ag + and 15 anionic ions including HPO 4 2 ˉ, CO 3 2 ˉ, HSO 4 ˉ , SO 4 2 ˉ, PO 4 3 ˉ, Fˉ, SO 3 2 ˉ, CH 3 COOˉ, HCO 3 ˉ, NO 2 ˉ,HSO 3 - ,Brˉ, S 2 ˉ, Clˉ and Iˉ at the final concentration of 100 μM.…”

Oil-Dispersible Green-Emitting Carbon Dots: New Insights on a Facile and Efficient Synthesis

“…In fact, after the separation, both the types of CDs show similar absorption bands in the visible range, distinct from the chemical groups or structures forming the CDs, in agreement with [ 24 ]. However, the possibility of safely inferring the exact origin of the electronic transitions giving rise to these bands is not trivial: similar absorption bands above 300 nm are often related to the n-π * transitions of the surface-related chemical groups of the CDs that form a system of multiple discrete energy states [ 29 , 43 , 44 , 47 , 48 , 49 ]. However, other reports [ 24 , 25 , 50 , 51 ] ascribe them to the π-π* and n-π* transitions, respectively, of the characteristic interconnected heteroaromatic units of the CDs.…”

DES-N-doped oxygenated carbon dot colloidal solutions for light harvesting and bio-imaging applications

“…S6, ESI †) indicating formation and stabilization of CDs in DESbased micelles wherein different emissions originated from different luminescence centres. 51 Blue emission normally originates from the surface defects and the green emission arises from molecular states with distinct energy levels. The (Fig.…”