Large two-photon cross sections and low-threshold multiphoton lasing of CdS/CdSe/CdS quantum shells.

Area of Science:

• Materials Science
• Quantum Optics
• Nanotechnology

Background:

• Colloidal quantum shells are spherical semiconductor quantum wells with potential in optical applications.
• Multiexciton physics is crucial for advanced optical experiments.

Purpose of the Study:

• Investigate the two-photon properties of CdS/CdSe/CdS quantum shells.
• Demonstrate their potential for upconversion imaging and as gain media.

Main Methods:

• Characterization of two-photon absorption cross-sections.
• Time-resolved measurements of biexciton lifetime and gain bandwidth.

Main Results:

• Large two-photon cross sections (0.4-7.9 × 10^6 GM).
• Long biexciton lifetimes (>10 ns) and broad gain bandwidth (>300 meV).
• Low thresholds for amplified spontaneous emission and lasing (as low as 1 mJ cm^-2).

Conclusions:

• CdS/CdSe/CdS quantum shells are excellent gain media for two-photon excitation.
• Their properties support multimodal amplified spontaneous emission.
• Quantum shell solids offer competitive or superior performance compared to other colloidal materials.