Room Temperature Phosphorescence Carbon Dots: Preparations, Regulations, and Applications

Hectogram-Scale Synthesis of Visible Light Excitable Room Temperature Phosphorescence Carbon Dots

Carbon dots (CDs) based room temperature phosphorescence (RTP) materials can be prepared via facile procedures and exhibit excellent photostability and biocompatibility. Furthermore, doping of hetero-atoms into CDs can afford multiple triplet levels. The RTP emission generated from the resultant CDs always displays outstanding dynamic behaviors and even can be efficiently excited by visible light. Given this, CDs-based RTP materials not only can be used for anti-counterfeiting but also exhibit great application potential in signage and illumination fields. In this contribution, a type of B, N, and P co-doped CDs are prepared in hectogram scale. Upon excitation by UV lamp and white LED, the obtained CDs emit green and yellow RTP, respectively, the lifetime of which are 851 and 481 ms, respectively. It is found that the luminescence color of the CDs can be further tuned. By controlling the degree of carbonization, the RTP color of the CDs can be facilely tuned from green to orange-red. Based on an energy transfer strategy, the luminescence color can be further tuned to red. Benefited from the dynamic and visible-excited colorful RTP emission, the application of these obtained CDs in anti-counterfeiting, fingerprint collection, and luminescent traffic signage are also explored.

Carbon Dots: A Bright Future as Anticounterfeiting Encoding Agents

Counterfeit products and data vulnerability present significant challenges in contemporary society. Hence, various methods and technologies are explored for anticounterfeiting encoding, with luminescent tracers, particularly luminescent carbon dots (CDs), emerging as a notable solution. CDs offer promising contributions to product security, environmental sustainability, and the circular economy. This critical review aims to highlight the luminescence responsiveness of CDs to physical and chemical stimuli, achieved through nanoengineering their chemical structure. The discussion will delve into the various tunable luminescence mechanisms and decay times of CDs, investigating preferential excitations such as up-conversion, delayed fluorescence, fluorescence, room temperature phosphorescence, persistent luminescence, energy and charge transfer, as well as photo-chemical interactions. These insights are crucial for advancing anticounterfeiting solutions. Following this exploration, a systematic review will focus on the research of luminescent CDs' smart encoding applications, encompassing anticounterfeiting, product tracing, quality certification, and information encryption. Finally, the review will address key challenges in implementing CDs-based technology, providing specific insights into strategies aimed at maximizing their stability and efficacy in anticounterfeiting encoding applications.

Tailored Fabrication of Full-Color Ultrastable Room-Temperature Phosphorescence Carbon Dots Composites with Unexpected Thermally Activated Delayed Fluorescence

The development of single-system materials that exhibit both multicolor room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) with tunable after glow colors and channels is challenging. In this study, four metal-free carbon dots (CDs) are developed through structural tailoring, and panchromatic high-brightness RTP is achieved via strong chemical encapsulation in urea. The maximum lifetime and quantum yield reaches 2141 ms and 56.55%, respectively. Moreover, CDs-IV@urea, prepared via coreshell interaction engineering, exhibits a dual afterglow of red RTP and green TADF. The degree of conjugation and functional groups of precursors affects the binding interactions of the nitrogen cladding on CDs, which in turn stabilizes triplet energy levels and affects the energy gap between S1 and T1 (ΔEST) to induce multicolor RTP. The enhanced wrapping interaction lowers the ΔEST, promoting reverse intersystem crossing, which leads to phosphorescence and TADF. This strong coreshell interaction fully stabilizes the triplet state, thus stabilizing the material in water, even in extreme environments such as strong acids and oxidants. These afterglow materials are tested in multicolor, time, and temperature multiencryption as well as in multicolor in vivo bioimaging. Hence, these materials have promising practical applications in information security as well as biomedical diagnosis and treatment.

Hour-Level Persistent Multicolor Phosphorescence Enabled by Carbon Dot-Based Nanocomposites Through a Multi-Confinement-Based Approach

Hour-level persistent room temperature phosphorescence (RTP) phenomena based on multi-confinement carbon dots (CDs) are reported. The CDs-based system reported here (named Si-CDs@B2O3) can be efficiently synthesized by a simple pyrolysis method compared to the established persistent RTP systems. The binding modes of CDs, silica (SiO2), and boron oxide (B2O3) are deduced from a series of characterizations including XRD, FT-IR, and TEM characterization. Further studies show that the formation of covalent bonds between B2O3, SiO2, and CDs play a key role in activating the persistent RTP and preventing its quenching. This is a rare example of a persistent RTP system that exhibits hourly persistent RTP under environmental conditions. Finally, the applications of Si-CDs@B2O3 are demonstrated for anti-counterfeiting, long-duration phosphorescence imaging, and fingerprinting. This synthetic strategy is expected to provide strong technical support for the preparation of persistent RTP CDs and pave the way for the synthesis of persistent RTP CDs in the future.

Achieving long-lived white circularly polarized luminescence from carbonized polymer dots via phosphorescence resonance energy transfer

Achieving white-light emission, especially long-lived white circularly polarized luminescence, is challenging. Herein, chiral phosphorescent carbonized polymer dots (CPDs) have been prepared by using chiral polymer sodium alginate and chiral small molecule L-lysine as precursors. Benefiting from the efficient triplet-to-singlet phosphorescence resonance energy transfer (PRET), CPD-based long-lived warm white CPL has been achieved for the first time. This study provides a universal strategy for the convenient and efficient preparation of CPD-based long-lived white CPL materials.

A carbon dot-based time-dependent color-changing room temperature phosphorescent material with facile synthesis

Carbon dots have attracted widespread attention due to their excellent optical properties and so on and are therefore used in various fields such as anti-counterfeiting. There are many reports on carbon dot-based room-temperature phosphorescent materials, but there are still fewer reports on carbon dot-based room-temperature phosphorescent materials with time-dependent color-changing properties. In this work, a time-dependent color-changing carbon dot-based room-temperature phosphorescent material with the ability to change from green to blue was successfully prepared by a simple one-pot heating method using hydroxyurea as the only raw material. In this process, hydroxyurea is used as both a carbon and nitrogen source, and in the process of material formation, hydroxyurea also partially forms cyanuric acid as a matrix to make the carbon dots uniformly dispersed in it. By blending the ratio of the dual emission centers of the carbon dots themselves, the final effect of time-dependent color-changing is achieved by taking advantage of the intensity changes and color differences of each emission center. The present work provides new ideas for the preparation of time-dependent color-changing carbon dot-based room-temperature phosphorescent materials.

Multiemitting Ultralong Phosphorescent Carbonized Polymer Dots via Synergistic Enhancement Structure Design

Advancing a metal-free room temperature phosphorescent (RTP) material that exhibits multicolor emission, remarkable RTP lifetime, and high quantum yield still faces the challenge of achieving intersystem crossing between singly and triplet excited states, as well as the rapid decay of triplet excited states due to nonradiative losses. In this study, a novel strategy is proposed to address these limitations by incorporating o-phenylenediamine, which generates multiple luminescent centers, and long-chain polyacrylic acid to synthesize carbonized polymer dots (CPDs). These CPDs are then embedded in a rigid B2O3 matrix, effectively limiting nonradiative losses through the synergistic effects of polymer cross-linking and the rigid matrix. The resulting CPD-based materials exhibit remarkable ultralong phosphorescence in shades of blue and lime green, with a visible lifetime of up to 49 s and a high phosphorescence quantum yield. Simultaneously, this study demonstrates the practical applicability of these excellent material properties in anti-counterfeiting and information encryption.

Chiral Phosphorescent Carbonized Polymer Dots Relayed Light-Harvesting System for Color-Tunable Circularly Polarized Room Temperature Phosphorescence

Carbonized polymer dots (CPDs) with a circularly polarized fluorescence property have received increasing attention in recent years. However, it is still a great challenge to construct circularly polarized room-temperature phosphorescence (CPRTP) CPDs. Herein, a simple approach to the synthesis of intrinsically CPRTP CPDs for the first time by utilizing sodium alginate and l-/d-arginine as precursors under relatively mild reaction conditions is presented. Notably, the CPDs exhibit both chirality and green RTP in solid states. Furthermore, color-tunable CPRTP is successfully achieved by engineering chiral light-harvesting systems based on circularly polarized phosphorescence resonance energy transfer (C-PRET) where the CPDs with green RTP function as an initiator of chirality and light absorbance, and commercially available fluorescent dyes with different emission colors ranging from yellow to red serve as the terminal acceptors. Through one-step or sequential C-PRET, the light-harvesting systems can simultaneously furnish energy transfer and chirality transmission/amplification. Given the multicolor long afterglow, lifetime-tunable, and CPRTP properties, their potential applications in multiple information encryption are demonstrated.

Chiral Aggregation-Induced Emission Carbon Dot-Based Multicolor and Near-Infrared Circularly Polarized Delayed Fluorescence via a Light-Harvesting System

Circularly polarized luminescence (CPL) materials are the research frontier of chiral luminescence. As a kind of luminescent carbon material, carbon dots (CDs) are expected to become excellent candidates for the construction of CPL materials. However, the construction of CD-based circularly polarized afterglow emission, especially multicolor and near-infrared emission, remains a great challenge due to aggregation-caused quenching and the instability of triplet excitons. In this work, we synthesized chiral CDs with aggregation-induced emission using dithiosalicylic acid and l/d-arginine as precursors through a one-step solvothermal method. Notably, the CDs exhibit green delayed fluorescence (DF) in poly(vinyl alcohol) films. Furthermore, multicolor and near-infrared circularly polarized delayed fluorescence is successfully realized via engineering a chiral light-harvesting system in which the CDs with green DF emission act as energy donors and fluorescent dyes with emission colors ranging from yellow to the near infrared serve as energy acceptors.

Pyrolysis of Al-Based Metal-Organic Frameworks to Carbon Dot-Porous Al2 O3 Composites With Time-Dependent Phosphorescence Colors for Advanced Information Encryption

Phosphorescent materials with time-dependent phosphorescence colors (TDPCs) have great potential in advanced optical applications. Synthesis of such materials is attractive but challenging. Here, a series of carbon dot-porous Al2 O3 composites exhibiting distinctive TDPC characteristics is prepared by high-temperature pyrolysis of Al-based metal-organic frameworks NH2 -MIL-101(Al). The composite synthesized at 700 °C (CDs@Al2 O3 -700) shows an obvious change in phosphorescence color from blue to green after removing the excitation light of 280 nm. Photophysical analysis reveals that two emission centers in CDs, namely carbon core and surface states, are responsible for the short-lived blue phosphorescence (96 ms) and long-lived green phosphorescence (911 ms), respectively. The combination of blue and green phosphorescence with different decay rates triggering the interesting TDPC phenomenon. CDs@Al2 O3 -700 has a significantly high phosphorescence quantum yield of up to 41.7% and possesses an excellent optical stability against water, organic solvents, and strong oxidants, which benefits from the multi-confinement of CDs by the porous Al2 O3 matrix through rigid network, strong space constraint, and stable covalent bonding. Based on the TDPC property, multilevel coding patterns composed of CDs@Al2 O3 are successfully fabricated for advanced dynamic information encryption.

High-efficiency NP-carbon dots above 60% with both delayed fluorescence and room-temperature phosphorescence

This report introduces a groundbreaking technique for synthesizing carbon dots (CDs) that display both delayed fluorescence and room-temperature phosphorescence. This achievement is made possible through a straightforward solvent-thermal reaction, followed by thermal treatment. The CDs are simultaneously provided with blue fluorescence and cyan afterglow, with an afterglow quantum yield (QY) of up to 60.47%, which is an expected figure for non-metallic CDs afterglow materials. Moreover, these CDs show an average afterglow lifetime of 1.11 s with a visually recognizable period of 16 s. We subsequently demonstrate the pragmatic application of CDs in cutting-edge fields such as anti-counterfeiting security and optical information storage.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.