Spectrally Tunable Solid State Fluorescence and Room‐Temperature Phosphorescence of Carbon Dots Synthesized via Seeded Growth Method

Abstract

A seeded growth method to produce colloidal carbon dots (CDs) through controlling the number of seeds and reaction time, which is demonstrated to be an effective way to tune their optical properties, is developed. Color‐tunable fluorescence of CDs with blue, green, yellow, and orange emissions under UV excitation is achieved by increasing the size of the seed CDs, with the color depending on the size of the π‐conjugated domains. Strong multicolor photoluminescence of powdered samples enables realization of efficient down‐conversion white‐light‐emitting devices with correlated color temperature ranging from 9579 to 2752 K and luminous efficacy from 19 to 51 lm W−1. Moreover, color‐tunable room‐temperature phosphorescence of CD powders is demonstrated in the broad spectral range of 500–600 nm. It is related to the presence of the nitrogen‐containing groups at the surface of CDs, which form interparticle hydrogen bonds to protect the CD triplet states from quenching, and to the existence of the polyvinylpyrrolidone polymer chains at the surface of CDs. The color‐tunable room‐temperature phosphorescence from CDs demonstrated in this work exhibits potential for data encryption.

Matrix‐Free and Highly Efficient Room‐Temperature Phosphorescence Carbon Dots towards Information Encryption and Decryption

“…Room‐temperature phosphorescence (RTP) materials, such as organometallic complexes, metal‐free pure organic compounds and carbon dots (C‐dots) have been of great concerns in many applications fields including bioimaging, sensing and information security owing to their characteristic long lifetime afterglow. Among these RTP materials, C‐dots possess a number of distinct merits such as facile preparation, relatively low manufacturing costs, low toxicity, and high luminescence efficiency .…”

“…As seen in Figure 2 (d-g), XPS spectrum of C 1s can be deconvoluted into three peaks at 284.6 eV, 285.2 eV and 286.6 eV, corresponding to CÀ C/C=C, CÀ N and CÀ O bonds, respectively. The XPS N 1s spectra contain three types of nitrogen bonds that can be assigned to CÀ N=C (399.0 eV), NÀ (C) 3 (400.6 eV), NÀ H (401.4 eV). The XPS O 1s spectra contain three types of oxygen bonds that can be assigned to P=O (530.7 eV), C=O (531.7 eV) and PÀ O/ CÀ O (532.6 eV).…”

Visible-Light-Excited Room Temperature Phosphorescent Carbon Dots

“…More importantly, matrix-free RTP CDs have also been prepared very recently based on the concept of crosslink enhanced emission (CEE), selfimmobilization fluorophores and specific elements (e.g., N, P and halogens) doping [37][38][39][40][41][42][43][44][45][46][47]. The reported matrix-free RTP CDs, however, only showed RTP emission colors from green to yellow and have to be excited by UV light as well [37][38][39][40][41][42][43][44][45][46][47]. To further expand the applications, it is significant to develop matrix-free RTP CDs holding long-wavelength (orange to red, and even to near infrared (NIR)) emissions and capable of being excited by visible-light, but this is still a formidable challenge.…”

“…Based on the prerequisites for activating RTP in organic compounds and matrix-free CDs (e.g., introducing heteroatom to improve intersystem crossing (ISC) and producing matrix-like structures to self-immobilize fluorophores in CDs), [38][39][40][41] herein, a facile and quick method is reported to prepare visible-light-excited matrix-free RTP CDs (named AA-CDs) with orange emission. As shown in Figure 1a, L-aspartic acid (AA) was taken as the carbon precursor, and the AA-CDs can be obtained by microwave-irradiation heating AA in the presence of ammonia water (see Materials and Methods section for details).…”

Designing Multicolor Dual‐Mode Lanthanide‐Doped NaLuF4/Y2O3 Composites for Advanced Anticounterfeiting

“…A group of fluorescent materials have been developed and applied in the information security and anticounterfeiting fields that can emit visible light under the excitation of an ultraviolet (UV) lamp or a near‐infrared (NIR) laser . High‐performance fluorescent materials mainly include Ln 3+ ‐doped materials, carbon dots, quantum dots, plasmonic materials, metal‐organic frameworks, etc. Compared to other fluorescent materials, Ln 3+ ‐doped fluorescent materials have emerged as a promising candidate because of their intrinsic multicolor luminescent properties, long fluorescence lifetime, excellent photochemical stability, and good biocompatibility …”