PLQY

Photoluminescence quantum yield (PLQY) is the ratio of photons emitted by a material to photons absorbed when the material is excited by light. It is a fundamental measure of emissive efficiency for materials such as organic dyes, quantum dots, perovskites, and phosphors. PLQY is unitless and typically expressed from 0 to 1 (0% to 100%). In many contexts PLQY is reported as an external quantum yield, while some studies distinguish internal quantum yield (IQY), which reflects radiative efficiency inside the material independent of light extraction losses.

Measurement of PLQY is commonly performed with an integrating sphere coupled to a calibrated light source. The sample is illuminated with a known photon flux, the emitted light is collected and integrated, and the PLQY is calculated as the number of emitted photons divided by the number of absorbed photons. Corrections may be needed for reflection, scattering, reabsorption, or re-emission effects, especially in solid films or highly scattering samples.

Factors influencing PLQY include material quality and purity, crystal or molecular structure, surface passivation, defect density, and the surrounding environment (solvent, matrix, or solid state). Temperature and excitation conditions also affect nonradiative decay pathways. Concentration quenching, aggregation, and reabsorption can reduce measured PLQY in concentrated or thick samples.

PLQY is widely used to screen and optimize materials for light-emitting diodes, displays, lasers, fluorescence imaging, and other optoelectronic applications. Typical high-performance materials can exhibit PLQY values near unity under favorable conditions, with lower values observed in less well-passivated or more quenching-prone systems.