Controllable Singlet–Triplet Energy Splitting of Graphene Quantum Dots through Oxidation: From Phosphorescence to TADF

Abstract

Long‐lived afterglow emissions, such as room‐temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), are beneficial in the fields of displays, bioimaging, and data security. However, it is challenging to realize a single material that simultaneously exhibits both RTP and TADF properties with their relative strengths varied in a controlled manner. Herein, a new design approach is reported to control singlet–triplet energy splitting (∆EST) in graphene quantum dots (GQD)/graphene oxide quantum dots (GOQDs) by varying the ratio of oxygenated carbon to sp2 carbon (γOC). It is demonstrated that ∆EST decreases from 0.365 to 0.123 eV as γOC increases from 4.63% to 59.6%, which in turn induces a dramatic transition from RTP to TADF. Matrix‐assisted stabilization of triplet excited states provides ultralong lifetimes to both RTP and TADF. Embedded in boron oxynitride, the low oxidized (4.63%) GQD exhibits an RTP lifetime (τTavg) of 783 ms, and the highly oxidized (59.6%) GOQD exhibits a TADF lifetime (τDFavg) of 125 ms. Furthermore, the long‐lived RTP and TADF materials enable the first demonstration of anticounterfeiting and multilevel information security using GQD. These results will open up a new approach to the engineering of singlet–triplet splitting in GQD for controlled realization of smart multimodal afterglow materials.

Carbon Dots: A New Type of Carbon-Based Nanomaterial with Wide Applications

“… 24 (g) Time-resolved information security using GQDs-based long-lived RTP/TADF. 28 Images reproduced with permission from refs ( 48 , 77 , 88 , 90 , 25 , 24 , and 28 ). Copyright 2018 American Chemical Society, 2019 WILEY-VCH, 2017 Royal Society of Chemistry, 2019 Royal Society of Chemistry, 2019 WILEY-VCH, 2018 WILEY-VCH, and 2020 WILEY-VCH.…”

Emergence of long afterglow and room temperature phosphorescence emissions from ultra-small sulfur dots

“…In this connection, luminescent nanomaterials made of pure elements such as carbon dots, graphene QDs, silicon QDs, and phosphorous dots have been extensively studied for the last few years. 11,[16][17][18][19][20] Recently, S-dots have attracted great attention owing to their intricate electronic properties and promising applicability as emitting and catalytic materials. [21][22][23] Sulfur is earth-abundant and has been used in many fields such as the production of sulfuric acid, lithium-sulfur batteries, potassium-sulfur batteries, supercapacitors, and in sulfur-modified polymeric and organic transformation materials.…”

Recent progress on graphene quantum dots‐based fluorescence sensors for food safety and quality assessment applications

“…For instance, GQDs embedded in boron oxynitride with lower oxidation (4.63%) exhibited a phosphorescence lifetime of 783 ms, and in the case of highly oxidized GQDs (59.60%) the lifetime value showed a decrement to 125 ms. The long-lived optical property of GQDs was utilized in anticounterfeiting and multilevel information security applications (Park et al, 2020). It has been well documented that two-dimensional materials have been successfully utilized to generate zero-dimensional QDs.…”