Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 25
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sample. This allowed the arm, and hence the fiber, to rotate freely with the sample as
the center of rotation. Due to the grading of the goniometer, the measurements were
taken every 50 from -15 from normal to 900. Measurement of the full range of
measurements (-90 to 90) was not possible due to the position of the incident beam
and the length of the fiber.
Excitation was achieved as with the other PL experiments, with the angle of
incidence of the laser determined to be -550 relative to normal. The reflected portion of
the laser signal at 550 was filtered out using a 325 nm line filter, and additional
background due to fluorescence of the fiber was subtracted out from the final spectra
using a reference glass sample. Figure 3.4 depicts the experimental layout used.
3.5 Time-resolved PL
Time-resolved PL measurements (TRPL) differ from normal PL measurements in
terms of both the excitation source and the detector used. In order to measure the time-
dependent emission of the sample, we first need a time-varying source. Were we to use
a CW excitation, we would only be able to measure a time-dependence during the
transient phase when the excitation source was turned on initially. After a short (< 10
ns) period, the system would reach equilibrium and thereafter there would be no time-
dependence to measure. Therefore this experiment uses a pulsed excitation source
instead of a CW source in order to excite the sample. It is important to note that the
frequency of the excitation (and duration of the pulse) plays a large role in determining
the sorts of interactions which can be studied using TRPL. Specifically, the frequency
should be slow enough that the system returns to the ground state after each pulse, and
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Llopis, Antonio. Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures, dissertation, May 2012; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc115113/m1/35/: accessed February 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .