Qd

QD is an initialism with multiple meanings across disciplines. In science and technology, the most common reference is quantum dot, a nanoscale semiconductor particle that exhibits quantum confinement.

Quantum dots are typically 2–10 nanometers in diameter; their electronic structure depends strongly on size, yielding a band gap that can be tuned across the visible spectrum. Common compositions include CdSe, CdS, and core–shell CdSe/ZnS, with surface ligands that provide solubility in organic or aqueous media. The emission is usually bright and spectrally narrow, enabling high color purity. Colloidal QDs can be integrated into inks for displays and lighting, in photovoltaics, or for bio-imaging and sensing. Core–shell architectures improve stability and quantum yield.

Synthesis often uses colloidal, high-temperature, hot-injection methods that control growth and passivation. Challenges include surface trap states, blinking at the single-particle level, non-radiative Auger recombination, and toxicity concerns from cadmium; these motivate cadmium-free alternatives such as indium phosphide QDs or lead-free perovskite QDs, though trade-offs in color quality and stability remain.

Other meanings: Quick disconnect, a detachable coupling used in hydraulic, pneumatic, electrical, and fluid systems to allow rapid disconnection and reconnection without tools.

In medical contexts, QD is an abbreviation for quaque die, Latin for once daily, used in prescriptions; interpretation requires careful labeling to avoid dosing errors.

See also: QLED, quantum dot displays, quantum dot solar cells.