RESUMO
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.
RESUMO
The investigation of the luminescence properties of CdTe/KBr composites with encapsulated quantum dots (QDs) of different sizes was performed and the influence of the KBr matrix on the luminescence properties of CdTe QDs was studied. Encapsulation of nanoparticles by a solid matrix caused a bathochromic shift in the luminescence peak and the shift value was the larger the smaller the size of the quantum dots. Interband quantum transition theory was used to explain the influence of the matrix on the luminescence properties of the capsulated CdTe QDs. Theoretical calculations showed that the observed QD luminescence peak corresponded to a 1 s-1 s electronic transition, and its low-energy shift after the transfer of QDs from dielectric water to the KBr matrix was due to a corresponding decrease in the depths of electrons and holes potential wells.