Overview
Quantum dots (QDs) are nanoscale semiconductor particles (2-10 nm) that exhibit quantum confinement effects, leading to size-dependent optical and electronic properties. Discovered in the 1980s, they bridge the gap between bulk semiconductors and discrete molecules. Their tunable bandgap allows precise control over emitted light wavelengths, making them invaluable for high-color-purity applications. Commercially, QDs are typically composed of groups II-VI (e.g., CdSe) or III-V (e.g., InP) elements. Core-shell structures (e.g., CdSe/ZnS) enhance stability and quantum yield. Recent advancements focus on heavy-metal-free alternatives like silicon or perovskite QDs for eco-friendly applications.
Physical and Chemical Properties
Quantum dots display unique size-dependent fluorescence due to the 'quantum size effect.' As particle size decreases, the bandgap widens, shifting emission to shorter wavelengths (blue shift). For example, CdSe QDs emit at 510 nm (2.4 nm diameter) to 650 nm (5 nm diameter). Their narrow emission spectra (FWHM <30 nm) outperform organic dyes. Surface chemistry dictates solubility and reactivity. Ligands like oleic acid stabilize colloidal QDs in organic solvents, while PEG or carboxylate groups enable water dispersion. Degradation risks include photo-oxidation and aggregation, mitigated by inert coatings or matrix encapsulation.
Main Applications
In displays, QDs enhance LCDs as color-conversion films (e.g., QD-LED TVs), achieving 100% NTSC color gamut. Samsung’s QD-OLED technology combines quantum dots with OLED for superior brightness and color accuracy. Solar cells utilize QDs for multi-exciton generation, potentially exceeding Shockley-Queisser limits. Biomedically, QDs serve as fluorescent probes for cellular imaging and diagnostics due to their photostability. They also enable optoelectronic devices like photodetectors and single-photon emitters for quantum computing. Emerging uses include anti-counterfeiting tags and photocatalysis.
Safety and Storage
Cadmium-based QDs pose environmental and health risks if improperly handled. OSHA mandates exposure limits for Cd (5 µg/m³). Always use fume hoods, gloves, and sealed containers. Aqueous QDs may require antibacterial agents (e.g., sodium azide) to prevent microbial growth. Storage varies by formulation: organic-phase QDs degrade upon oxygen/light exposure and should be argon-purged. Powdered QDs need desiccants. For long-term stability, some suppliers offer polymer-encapsulated or glass-embedded formats. Disposal must follow hazardous waste regulations.
B2B Procurement Guide
Industrial buyers should prioritize suppliers with ISO 9001 certification and batch-to-batch consistency guarantees. Key specifications include photoluminescence quantum yield (>80% for premium grades), FWHM (<25 nm), and customizable surface functionalization (e.g., -NH2 for bioconjugation). Bulk orders (kg-scale) may negotiate 10-20% discounts. Lead times vary: standard CdSe/ZnS QDs ship in 2 weeks, while custom InP formulations may require 6-8 weeks. Always request material safety data sheets (MSDS) and independent test reports for heavy metal content.
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