- Cadmium selenide (CdSe) is an inorganic compound composed of cadmium and selenium, and it belongs to the family of II–VI semiconductors. In its pure form, CdSe can appear as red, orange, or black crystals depending on its particle size and crystalline structure.
- It occurs naturally in the mineral cadmoselite, though this mineral is extremely rare. CdSe crystallizes mainly in two forms: the hexagonal wurtzite structure and the cubic zinc blende structure, with both arrangements featuring cadmium ions (Cd²⁺) tetrahedrally coordinated to four selenium ions (Se²⁻) and vice versa. These crystal structures, along with quantum size effects in nanoscale particles, strongly influence CdSe’s optical and electronic properties, making it a material of great importance in optoelectronics.
- Synthetically, cadmium selenide can be prepared by the direct combination of cadmium and selenium at high temperatures, or by precipitation from cadmium salt solutions with hydrogen selenide gas. In the modern semiconductor industry, CdSe is frequently produced as nanocrystals or quantum dots using colloidal synthesis methods, allowing precise control over particle size, shape, and surface chemistry. Such control is critical because the bandgap of CdSe can be tuned by particle size due to quantum confinement effects—smaller nanocrystals emit bluer light, while larger ones emit redder light.
- CdSe has a direct bandgap of about 1.74 eV in its bulk form, making it sensitive to visible light and well-suited for optoelectronic applications. It is widely used in photodetectors, light-emitting diodes (LEDs), semiconductor lasers, and photovoltaic cells. In thin-film solar cells, CdSe can serve as an absorber layer or as part of a multilayer device to improve light harvesting. Quantum dots of CdSe have revolutionized display technologies, providing highly saturated and tunable colors in modern QLED televisions and monitors. They are also used in biomedical imaging and biosensing, where their fluorescence can be tailored for specific detection purposes.
- Beyond electronics and optics, CdSe has been studied for photocatalytic applications, including hydrogen production from water and degradation of environmental pollutants under light irradiation. When combined with other semiconductors, such as titanium dioxide (TiO₂), CdSe can form heterojunctions that enhance charge separation and improve photocatalytic efficiency. These properties make CdSe a material of interest for renewable energy and environmental remediation research.
- However, cadmium selenide is highly toxic, both because of cadmium’s well-known health hazards and the potential toxicity of selenium compounds. Inhalation or ingestion of CdSe dust or fumes can cause severe respiratory and systemic damage, kidney failure, and it has been classified as a human carcinogen. Environmental contamination is also a serious concern, as cadmium can persist in soil and water and bioaccumulate in living organisms. Consequently, the handling, use, and disposal of CdSe are strictly regulated in many countries, and strict safety protocols—such as glove use, fume hood operation, and sealed waste disposal—are mandatory in laboratories and industrial settings.
