What Is Meant By 100% QY QDs?
Quantum dots – often abbreviated to QDs – are nanoscale semiconducting crystals that glow following illumination; otherwise known as photoluminescence. When light strikes a QD, electrons in the crystal absorb its energy and enter an excited state. These electrons gradually begin to relax back to a ground state, losing the energy they have absorbed. This is what causes QDs to emit light of lower energy than the absorbed light. In this article, we will explore the efficiency of quantum dots and introduce the concept of 100% QY QDs.
Explaining the Photoluminescence of QDs
QDs emit characteristic wavelengths based on their chemistry and geometry. Most of the relevant literature focuses on crystal size to define how and why QDs emit the light that they do.
For instance: A small nanoparticle has a large energy difference between its ground and excited states, which means it will emit shorter wavelength radiation. Conversely, large nanoparticles have a smaller energy difference, thus they emit longer wavelengths. This has given rise to the popular assumption that small QDs emit vivid blues while large QDs emit deep reds. Yet, size-dependence is a limiting factor in terms of absorption and emission efficiency.
Understanding Quantum Yield
Quantum yield is a measure of QD efficiency which is expressed as a function of the Greek letter phi (Φ). Research and development into 100% QY QDs have largely proven fruitless, given the sheer range of non-radiative processes that occur in the femtoseconds between absorption and emission. Even complex multi-shell QDs experience some form of luminescent quenching which results in a practical maximum QY of 90%.
Attaining 100% QY QDs
Research into 100% QY QDs has increasingly focussed on novel nanomaterials in which photoluminescence is more chemistry-dependant than size-dependant. Metal halide perovskites are among the front-runners in this field. They can be fine-tuned to emit high-purity peak wavelengths based primarily on their composition, which means they can be implemented without a core/shell structure. A symptom of this is dramatically improved absorbance per gram characteristics with quantum yields approaching the previously unattainable maximum of 100%.
100% QY QDs from Avantama
Avantama is one of the world leaders in QD synthesis, routinely developing unique chemical formulations for a global customer base. We are continuing to leverage our expertise in pushing the efficiency of our solutions to realize practical 100% QY QDs for functional applications. If you would like to learn more, simply contact a member of the Avantama team today.