Recently, Professor Wang Yue of Nanjing University of Science and Technology and others have achieved high-quality environmentally friendly ZnSeTe-based quantum dots through the regulation of excited states by cooling engineering, demonstrating the feasibility of environmentally friendly quantum dots in practical applications.
Currently, quantum dots are a promising luminescent material, but the realization of high-quality environmentally friendly quantum dots (QDs) remains challenging because of its efficient but difficult-to-achieve non-radiative composites inside. By studying the effect of cooling engineering on the regulation of excited states, the above team successfully demonstrated the feasibility of high-quality ZnSeTe core-shell quantum dots. The results were published in the journal SCIENCE CHINA Materials.
Image courtesy of Science china Materials
According to the paper, scientists recently discovered that ZnSeTe-based quantum dots that do not contain heavy metals are able to display tunable blue-green emission by changing the se-te ratio. Therefore, as an environmentally friendly material, it has broad application prospects in optoelectronic devices. However, ultrafast thermal carrier capture and banded carrier capture are the main reasons for the inefficiency of ZnSeTe quantum dot emission efficiency.
To improve luminescence efficiency, the researchers suppressed the above processes by designing cooling engineering, including using different cooling rates to cool the reaction solution, and using ice water cooling, natural air cooling, and furnace cooling to adjust the rate at which the reaction terminated or cooled. Cooling engineering is an important part of regulating the excitation state composite of ZnSeTe-based quantum dots and improving the quality of quantum dots.
Subsequently, the research team analyzed the potential mechanisms in combination with electron and spectral characterization, and found that the cooling process had a significant impact on the crystallization quality and shell thickness of ZnSeTe-based quantum dots. The team's cooled-optimized ZnSeTe quantum dot exhibits high quantum luminous efficiency (>90%), exceeding previous world records, with good stability, and the quantum dot is comparable to traditional cadmium selenide (CdSe) quantum dots.
The experimental picture is from the paper
In cadmium selenide quantum dots, the non-radiative composite process can already be controlled by synthetic methods, so it has high-quality luminescence properties and has excellent stability, but due to the heavy metal element of cadmium, cadmium selenide material has a strong irritation, and contact can cause people nausea, headache and vomiting. Therefore, the heavy metal content in it will likely hinder its commercial application.
The research team also conducted comparative experiments on the light stability of cadmium selenide, cadmium sulfide (CdS), and zinc sulfide (ZnS) quantum dots. Under similar ultraviolet light illumination, the luminous intensity of all three quantum dots was reduced by about 40%. Overall, the team designed the optimized non-toxic ZnSeTe-based quantum dots with higher stability, comparable to the stability of the above three quantum dots. This observation contributes to the practical application of photoelectrics after ZnSeTe quantum dots.
Graph of experiments and results of WLED, picture from the paper
White light-emitting diodes (WLEDs) based on ZnSeTe quantum dots exhibit excellent optical properties, including a high color rendering index of 80 and a good correlated color temperature of 7391K (Kelvin temperature units). In addition, considering the potential of quantum dots to have high modulation bandwidth and high data transmission rate in optical communication systems, the high-performance WLED also has good optical communication capabilities and can be used as a light source for environmentally friendly visible light communication.
The research results of Professor Wang Yue and others of Nanjing University of Science and Technology achieve high-quality ZnSeTe quantum dots through cooling engineering such as cooling rate control method, which shows the feasibility of environmentally friendly quantum dots in practical applications.