It is well known that cadmium-based quantum dots will hinder their eventual research transformation and commercialization due to the inherent toxicity of cadmium. Therefore, less toxic semiconductor quantum dots, such as CuInS2/ZnS and transition metal (Mn, Cu) doped, have gained increasing attention. The luminescence size and composition of these cadmium-free quantum dots are adjustable, and the luminescence efficiency can reach 70-85%, which is suitable for illumination and display and have good application prospects in solar cells, biological detection and imaging.
Fig.1 Photoluminescence spectra of CuInS2/ZnS quantum dots with different sizes
Due to avoiding the negative effects of heavy metal cadmium, cadmium-free green environmental protection quantum dots with good luminescence efficiency and stability have been applied to display and biological imaging.
- Display fields：Cadmium-free quantum dots can provide strong monochromatic light in the red and green light regions, and have nonlinear shape coefficient, which makes the color of the image more realistic, and has higher brightness and better energy saving effect, so it can be well applied in the display field. Moreover, quantum dot clay polymer composite film has the advantages of transparency, flexibility, light weight, durability and low price, which overcomes the shortcomings of traditional polymer materials in transparency, thermal stability, barrier property and solubility resistance, so it can be better applied in the research of flexible display.
Fig.2 Quantum dot display
- Biological imaging: Quantum dots have been widely used as fluorescent biological probes in biomedical imaging because of their excellent optical properties. The early fluorescent probes of quantum dots were mainly cadmium-containing quantum dots, which may be exposed to cadmium ions when applied to biological samples. Therefore, many cadmium-free quantum dots have been developed in recent years. Compared with traditional cadmium-containing quantum dots, cadmium-free quantum dots have more stable covalent bonds and better biocompatibility, and are considered to have greater potential for biomedical applications.
Fig.3 In vivo fluorescence imaging of the nude mouse bearing a sub-cutaneous tumor 
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- Ke Ding.; et al, Magnetically engineered Cd-free quantum dots as dual-modality probes for fluorescence/magnetic resonance imaging of tumors. Biomaterials, 2014, 35: 1608-1617.