- Cadmium sulfide (CdS) is an inorganic compound composed of cadmium and sulfur, belonging to the family of II–VI semiconductors. In its pure form, CdS appears as a yellow crystalline solid, although its shade can range from pale yellow to orange depending on impurities and particle size.
- It occurs naturally as two rare minerals: greenockite (hexagonal wurtzite form) and hawleyite (cubic zinc blende form). In both crystal structures, each cadmium ion (Cd²⁺) is tetrahedrally coordinated to four sulfide ions (S²⁻), while each sulfide ion is similarly surrounded by four cadmium ions. This arrangement is responsible for the compound’s characteristic semiconducting properties, which make it valuable in electronics, optics, and pigment production.
- Cadmium sulfide can be produced synthetically by several methods, including the direct combination of cadmium and sulfur at high temperatures, precipitation from cadmium salt solutions using hydrogen sulfide gas, or chemical vapor deposition techniques for thin-film applications. The material’s bright yellow color and stability led to its long-standing use as the pigment cadmium yellow, prized in art, plastics, and ceramics for its high opacity, resistance to fading, and thermal stability. However, due to cadmium’s toxicity, the use of CdS pigments has been significantly restricted in modern times.
- One of CdS’s most important roles is in semiconductor technology. It has a direct bandgap of about 2.42 eV at room temperature, making it sensitive to light in the visible spectrum. This property allows CdS to function as a photoconductor, photovoltaic material, and light sensor. It has been widely used in photoresistors (light-dependent resistors), photodetectors, and as a window layer in thin-film solar cells—often in combination with copper indium gallium selenide (CIGS) or cadmium telluride (CdTe) to optimize light absorption and efficiency. CdS thin films are typically prepared via chemical bath deposition, sputtering, or vapor-phase techniques to achieve precise control over thickness and grain size.
- Beyond electronics, CdS is used in optical devices, laser systems, and electro-optical modulators, particularly in research exploring nonlinear optical behavior. Nanostructured CdS, such as quantum dots, has gained attention in modern materials science for applications in light-emitting diodes (LEDs), photocatalysis for hydrogen generation, and environmental pollutant degradation, owing to its tunable optical and electronic properties at the nanoscale.
- Despite its wide range of uses, cadmium sulfide is toxic and poses both occupational and environmental hazards. Cadmium is a bioaccumulative heavy metal that can cause kidney damage, skeletal weakening, respiratory problems, and is classified as a human carcinogen. Inhalation of dust or fumes, ingestion, or prolonged skin contact can be dangerous. Environmental contamination from CdS can occur through improper disposal, leading to soil and water pollution and entry into the food chain. As a result, the production, handling, and disposal of CdS are strictly regulated in many countries, and appropriate safety measures—including protective clothing, dust control, and hazardous waste management—are essential in all stages of its use.
