Assembling of Sulfur Quantum Dots in Fission of Sublimed Sulfur

Abstract

A novel kind of quantum dots, sulfur quantum dots (S dots), is synthesized by simply treating sublimated sulfur powders with alkali using polyethylene glycol-400 as passivation agents. The synthesized S dots exhibit excellent aqueous dispersibility, eminent photostability and temperature dependent photoluminescence (PL). An "assemble-fission" mechanism is proposed for the S dots formation in which "assembling" and "fission" are involved and contest each other. The ultimate morphologies of the S dots are dependent on the balance of the two forces. Guided by the assemble-fission mechanism, weakening the assembling effect is beneficial for obtaining monodisperse S dots, which can be achieved by pretreating of sulfur powder with nitric acid. PL wavelength of the S dots has been successfully tuned between green and blue light (from 550 to 440 nm) by simply controlling reaction time. A satisfactory quantum yield of 3.8% is obtained. Significant electrochemiluminescence of the S dots is observed in an annihilation reaction. Chemiluminescence from the S dots has been observed by direct oxidation. Taking advantage of unique and inherent antimicrobial activity of the sulfur particles, it is believed that this new emerging luminescent nanomaterial is highly promising in the development of new types of optoelectronic devices and tracer for live cells, in vivo imaging and diagnostics.

Hydrogen Peroxide Assisted Synthesis of Highly Luminescent Sulfur Quantum Dots

“…Sublimated sulfur powder, PEG, and NaOH were mixed together and stirred at 70 8 8C, similar to the process reported by Shen and co-workers. [12] Theyellow sulfur powder gradually dissolved, and the colorless mixture changed to light yellow,o range,a nd red during the heating process,f ollowed by the fading of color to light yellow with extension of heating time to 5h,c onsistent with previous report. [12] Theas-obtained product, which we denote as Sdots, was non-luminous under radiation of UV light.…”

“…[12] Theyellow sulfur powder gradually dissolved, and the colorless mixture changed to light yellow,o range,a nd red during the heating process,f ollowed by the fading of color to light yellow with extension of heating time to 5h,c onsistent with previous report. [12] Theas-obtained product, which we denote as Sdots, was non-luminous under radiation of UV light. Ar elatively strong green emission appeared immediately after injecting H 2 O 2 into the non-luminescent Sd ots,a ccompanied by al ightening of the solution color and massive generation of gases.T he green luminescence changed to an intense blue emission upon continuous injection of H 2 O 2 (Supporting Information, Movie S1).…”

“…[8] Consequently,e fforts have been made to develop non-toxic and even heavy metalfree QDs,w hich were mainly focused on InP-based and CuInS 2 -based QDs, [9] and these efforts have recently been extended towards elemental compounds,s uch as carbon and the related materials, [10] silicon, [11] and sulfur. [12] Among the latter,s ulfur QDs (SQDs) offer an added advantage of their inherent antimicrobial properties. [1a,2] Several attempts have been devoted to synthesize SQDs by employing wet chemistry routes,a nd to demonstrate and improve their photoluminescence (PL).…”

“…[13] Shen and co-workers proposed at op-down method to convert sublimated sulfur into SQDs through an "assemble-fission" reaction, which produced blue emitting material with aP LQ Yof3 .8 %, after 125 ht reatment. [12] Despite the efforts mentioned above,nobreakthrough has been achieved so far on the possible applications utilizing SQDs as efficient phosphors,f or example for down-conversion LEDs.T his is due to the absence of convenient and straightforward synthetic methods,a nd ar ather modest PL QY (less than 4%)o fd emonstrated materials which are way below those realized for traditional QDs and other phosphors.…”

“…[14] Moreover,b oth the blue and green emissive SQDs showed an excitation-dependent emission, with the peak shifting towards longer wavelength (from 430 to 520 nm) when the excitation wavelength varied from 340 to 440 nm (Figure 2f,g;S upporting Information, Figure S3), consistent with the previous work. [12] This could be attributed to the inhomogeneous size distribution of the particles,w hich possess size-dependent emission color.T his is also consistent with the finding that broader emission linewidths and more obvious excitation-dependent emission phenomenon were observed for the green SQDs than for the blue emissive SQDs. Figure 2h shows the UV/Vis absorption spectra of Sdots, and of SQD samples obtained after injecting different amounts of H 2 O 2 (0.75, 3.75, and 7.5 wt %).…”