Quenching‐Resistant Polymer Carbon Dot Preserving Emission Color Consistency in Solid‐State

Abstract

Recently, Rogach's group realized solidstate-luminescent CD/silica composite, which possessed high quantum yield (QY) and PL output with relatively high CD loading (19.2 wt%) by gelation. [18] However, this process was limited to hydroxyl-rich CD only and still suffered from aggregation in extremely high concentration.Fundamental solution is to develop a selfquenching-resistant CD even without dispersion matrices. Polymer CD (PCD), a polymer-like CD consisting of crosslinked matrix and sub-fluorophores, has been studied for solid-state luminescence because crosslinking may prevent π-π interaction. [20][21][22][23] Several groups synthesized quenching-resistant PCD, but those showed red-shifted emission with noticeable color change compared to solutionstate fluorescence. [24][25][26][27] Such spectral shift in solid-state usually occurs with nonradiative decay competitively, which leads to a decrease of QY. In addition, the emission color change in solidstate needs additional optimization process for the fabrication of optoelectronics, so that the energy transfer as an origin for ACQ and red-shift should be strictly avoided.Herein, we synthesized a blue-emitting PCD with the same emission center at 434 nm in both solution-and solid-state through a hydrothermal reaction. By structural and spectroscopic analysis, the origin of solid-state luminescence was investigated. We further identified a reason for the emission color consistency of PCD from dilute solution to powder form by comparing with CD that showed red-shifted emission in solid-state. We also fabricated LED using PCD as a color-converting layer, and it had a luminous efficacy of 12.03 lm W −1 without significant color change even with extremely high loading fraction of 50 wt%. With the increased loading fraction (20 wt%), we enhanced brightness of our LED up to four times compared to the LED fabricated with conventional low loading fraction (0.1-5 wt%) using PCD. Compared to red-shifted CD (RCD)-based LED with the conventional loading fraction, the luminous flux of PCD-based LED with 20 wt% increased by 3 to 15 times. This result would be a great interest to those who study CD-based LED. Results and DiscussionSolid-state luminescent polymer carbon dot (PCD) was synthesized using citric acid (CA) and diethylenetriamine (DETA) through a hydrothermal reaction at 70 °C (Figure 1a). Product Solid-state luminescent carbon dot without dispersion matrices is studied to overcome aggregation-caused quenching, but it usually shows spectral shift between solution-and solid-state accompanying a dramatic decrease of fluorescence intensity, which hinders a real application. Herein, polymer carbon dot (PCD) showing solid-state luminescence without red-shift is synthesized by low-temperature reaction. The PCD solution and solid have the same emission peaks at 434 nm and similar absolute quantum yields of 68.2% and 62.7%, respectively, which is uncommon feature compared to other carbon dots. The mechanism for solid-state luminescence and emission color consistency is invest...

Aggregation and luminescence in carbonized polymer dots

“…[110] By designing molecular fluorophores and avoiding carbonization, Kim et al achieved the same fluorescence performance in solid-state as that in solution state 8A). [111] They used CA and diethylenetriamine through a hydrothermal reaction at 70 • C for 48 h to synthesize CPDs. With CA and diethylenetriamine as the precursor, molecular fluorophore 1-(2-aminoethyl)-5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]-pyridine-7-carboxylic acid (AEIOP) (Table 1) can be produced.…”

Carbon dioxide derived carbonized polymer dots for multicolor light-emitting diodes

“…Molecular-state and core-state fluorescence are two widely proposed luminescence mechanisms. 49 Here, the emission of the carbonyl clusters of the CPDs belonged to the category of the molecular-state luminescence mechanism.…”

Simple Strategy for Scalable Preparation Carbon Dots: RTP, Time‐Dependent Fluorescence, and NIR Behaviors

“…[ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ] The CPDs resolve this problem at some level, but often encounter redshifted emission with noticeable color change compared to solution‐state fluorescence (Figure 3b ). [ 37 , 43 , 44 , 45 ] In previous reports, nonconjugated small molecules and linear polymers were chosen to prepare CPDs, which could avoid any possible conjugated components. [ 43 , 44 , 45 ] On the contrary, as shown in Figure 3e , M‐CDs give an emission maximum at about 472 nm (blue solid‐state fluorescence) under the excitation of 365 nm UV light, which prepared via “bottom‐up” reaction using conjugated small molecules as precursor, may appear redshifted emission in the solution state in theory.…”

“…[ 32 , 33 , 34 ] However, if too many CDs are introduced into the solid matrices, the ACQ effect still exists, and only 0.1–1 wt% of CDs can be used in the supporting media. [ 35 , 36 , 37 ] Therefore, it is necessary to develop the matrix‐free solid‐state luminescent CDs.…”