Two-step light conversion with quantum dots inside non-linear crystals

Up-conversion of infrared (IR) to visible light is demonstrated via an unconventional two-step process combining second harmonic generation with photoluminescence. This is achieved in a composite material formed by single crystals of KH₂PO₄ (KDP), in which CdTe/CdS quantum dots (QDs) are embedded during a crystal growth. The second harmonic generation from the IR laser frequency in KDP takes place, and then, generated light is absorbed by QDs and luminescence is emitted. Compared to the most common up-converting materials based on lanthanide ions, our novel composites use only abundant elements and have several other properties with application potential: the excitation and emission can cover a broader spectral range, and the response is much faster (ns compared to ms) and is strongly dependent on the direction of the incident beam.