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Spectral and Temporal Response of UV-pumped Colloidal Quantum Dots in Polymer, Thin-film, and Additively-manufactured Structures
An interesting question regarding colloidal quantum dots (CQDs) was how do they compare in terms of both their photoluminescence (PL) spectra and UV-Vis PL lifetime decays in various structures? This paper characterized both of these measurements using six commercially available CQD materials, these being: CdS, CdSe, CdSe nanoplatelets (NPLs), CdSe/ZnS, InP/ZnS, CuInS/ZnS. These nanocrystals were tested in the following structures: CQD-loaded polymer matrix, thin-film, and CQDs dispersed within a 3D printed honeycomb structure. Over the course of the experiments the following effects were observed: Charge-transfer (CT), Frster resonance energy transfer (FRET), and thermal oxidation. The time it took for CQD structures to decay from a experimentally derived modeled normalized intensity of 100% to 0.1% from UV-Vis excitation showed that the slowest decaying CQD loading structure was thin-film (12 ns to > 144 ns) while the fastest structure was CQD-loaded polymer matrix (945 ps to 20 ns). The 3D printed structure utilized SU-8-5 photoresist as a capping polymer to contain the CQDs. This resulted in all of the UV-Vis PL decay spectra for each nanocrystal material to become similar in values until the normalized intensity went below 1%. The 100% to 0.1% normalized intensity decay time for the 3D printed structure was from 10 ns to 44 ns. Out of all of the nanomaterials tested under UV excitation, CdS was demonstrated to be the fastest PL decaying CQD with a 100% to 50% normalized intensity decay time as 545 ps when loaded within a polymer matrix.
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