Boron Nitride Quantum Dots with Solvent‐Regulated Blue/Green Photoluminescence and Electrochemiluminescent Behavior for Versatile Applications

Abstract

such as layered transition metal dichalcogenides (TMDs), [2] hexagonal boron nitride (h-BN), [3] metal halides, [4] and black phosphorus, [5] which opened up a new horizon for a novel class of low-dimensional systems with superior properties for applications in optoelectronics, [6] energy conversion, [7] and catalysis. [8] Among these, h-BN nanosheet has its peculiar and fascinating properties such as good electrical insulation, [9] high-temperature stability, [10] high mechanical strength, [11] large thermal conductivity, [12] low toxicity and chemical stability, [13] leading to a variety of potential applications as both structural and electronic materials. [14] With further reducing the size of the layered BN sheets to less than 10 nm, 0D BN quantum dots (BNQDs) with excellent fluorescence properties and good dispersibility can be endowed due to the quantum confinement, edge effects, and defect centers. [13][14][15] Combining with the intrinsic properties of BN, BNQDs were supposed to be promising agents in biological and optoelectronic applications. [15b] However, compared with the widely studied 2D BN nanosheet, [9][10][11]16] BNQDs were much less reported than expected. [13][14][15] First, further exploration is required for the preparation of desired BNQDs products. BNQDs were initially prepared via high intensity ultrasound and subsequent refluxing. [14a] Allwood et al. have also successfully fabricated monolayer BNQDs via three steps of potassium-intercalation, deintercalation, and disintegration of BN edges, but only low quantum yield (QY) of 2.5% was achieved. [15a] Recently, sonication-solvothermal strategy was found to be a facile and universal method for the generation of BNQDs with relatively high QY of 8.6% or 19.5%. [13,15b] Although the filling factor of the autoclave, synthesis temperature and reaction time in the solvothermal process have been investigated, [13] little attention has been paid to how different solvents affect the properties of the BNQDs, which is usually an important parameter to influence the optical properties and QYs of the zero-dimensional QDs. [17] Second, besides the most frequently studied PL properties, electrochemiluminescence (ECL) is also an interesting characteristic Exploration of novel optical features, generation mechanisms, and versatile applicability of boron nitride quantum dots (BNQDs) is still in nascent stage. Herein, BNQDs are prepared using liquid exfoliation-solvothermal treatment of bulk BN in three different solvents. The photoluminescence of BNQDs is blue in ethanol (or N,N-dimethylformamide (DMF)) and green in N-methyl-2-pyrrolidone (NMP) under the same UV-irradiation, respectively.The quantum yields (QYs) and average lateral sizes of the BNQDs are 12.6% and 4.1 ± 0.2 nm, 16.4%, and 2.8 ± 0.3 nm, as well as 21.3% and 2.0 ± 0.2 nm in solvents of ethanol, DMF, NMP, respectively. The distinct sizes, QYs, and optical properties of the BNQDs are found to depend on the polarity of these solvents. Different BNQDs can be chosen on-demand for versatile...

Preparation of Ti3C2Tx MXene‐Derived Quantum Dots with White/Blue‐Emitting Photoluminescence and Electrochemiluminescence

“…As suggested, the higher is the solvent polarity, the interaction of organic solvents toward the 2D nanosheets should be stronger, resulting in much easier exfoliation of the layered nanosheets to QDs. As a result, the higher polarity of the solvent would lead to the smaller diameter and higher QYs of the QDs . However, the polarities of solvents herein are in the order of DMSO (7.2) > DMF (6.2) > ethanol (4.3), which is a little different from the sequences of the lateral sizes and QYs of the as‐obtained MQDs.…”

“…All the three MQDs exhibited excitation‐dependent PL features that first enhanced and then reduced accompanying with the increasing excitation wavelength. As shown in Figure S4 (Supporting Information), when the excitation wavelength increased from 310 to 690 nm, 250 to 560 nm, or 250 to 450 nm, the emission peaks of s‐MQDs, f‐MQDs or e‐MQDs shifted gradually from 520 to 750 nm, 450 to 600 nm, or 330 to 520 nm, respectively . Accordingly, blue fluorescence was observed for e‐MQDs and f‐MQDs, while white one for s‐MQDs under 365 nm UV irradiation.…”

“…In addition, all the other metal ions did not exhibit obvious influence on the PL intensities of all the three MQDs. The PL quenching of MQDs via Fe 3+ addition should result from the coordination between Fe 3+ and the oxygenous groups, especially the carbonyl ones (CO), on the surfaces of MQDs (Figure B) . As can be obtained from the XPS characterization, no CO group can be obtained in s‐MQDs (Figure E).…”

“…As indicated, the ECL intensity reached highest at pH 7.0 and decreased in both lower and higher pH values, showing the natural condition should be the optimum one for the background solution using in this ECL system. The influence of the buffer pH on the ECL signal should be attributed to the instable free radicals (SO 4 •− ) in acidic or alkaline conditions . The results showed that the as‐prepared MQDs were suitable for application in physiological conditions.…”

“…[6b] Additionally, it was suggested that a higher temperature of 200 °C would lead to the formation of highly fluorescent amphiphilic carbide‐derived graphene QDs . However, although the solvents applied are usually determining in the size, optical properties, and quantum yields (QYs) of the QDs, the solvothermal method for MQDs preparation has been paid little attention to the their effects on the properties of MQDs. Besides the PL characteristics, electrochemiluminescence (ECL) is also regarded as a vital property to assess the significant abilities and to widen the utility of the QDs .…”