CHARACTERIZATION OF CARRIER DECAY MECHANISMS AND QUANTUM YIELD IN COLLOIDAL UPCONVERTING NANOSTRUCTURES
Date
2018-05
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
With the continued rise to prominence of solar energy, increasing e ort is being
focused on developing more e cient solar energy harvesting technologies. Of those
technologies, photon upconversion materials have been demonstrated by simulation to
o er large potential e ciency boosts. While the systems that can perform photon
upconversion are varied, this study focuses on CdSe(Te)/CdS/CdSe nanorod upcon-
verting heterostructures. In this study, key aspects of the upconversion mechanism
within these structures are examined, and the results are compared between samples
with di erent levels of Tellurium doping within the absorber quantum dot to deter-
mine the e cacy of Te-doping as a design parameter for heterostructure optimization.
For each structure, photoluminescence and upconversion PL measurements are taken
to identify the presence of upconverted light. The dependence of the intensity of up-
conversion on the incident photon
ux is then measured to assess the nature of the
upconversion phenomenon. Time-resolved PL measurements are taken to obtain the
decay lifetimes associated with carriers that can radiatively recombine. Finally, the
e ciency of each structure is probed through upconversion quantum yield (UCQY)
measurements in a precisely calibrated integrating sphere. While successful upconver-
sion is observed in each structure, power-dependent measurements indicate that the
upconversion does not obey the desired purely two-photon mechanism. Moreover, the
structures upconvert with low e ciency, producing UCQY values less than 0.001%.
However, trends between the structures indicate that adjusting the Te-doping has not
had its desired e ect, but has instead caused unintended changes in the structures, such
as a pronounced inhomogeneity within the absorber quantum dot. To isolate the e ect
of Te-doping and to further optimize the structures, the e ect of this inhomogeneity
must be thoroughly examined in future studies.
Description
Keywords
chemical engineering, carrier decay mechanisms, nanostructures