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Zinc Oxide Nanostructures
480 nm can clearly be observed in the EL spectrum, the irst peak
at 450 nm is attributed to the excitonic transition in PFO [59]. The
second peak at 480 nm represents a irst-order vibronic transition
of PFO [59]. On the other hand the EL spectrum demonstrated a
broad green emission centered at 532 nm as shown in Fig. 6.8a that
can be ascribed to the deep level defects in ZnO. It is known that
ZnO NRs grown by the solution method present a large number of
defects [60]. The PFO also has defect emission in this range due
to the formation of the luorenone agglomerates or so called keto
defect during electro-(photo)oxidation [61]. The reason for this
could be when a luorenone defect is formed, the alkyl chain is lost,
favoring local interchain interaction between the PFO backbone
[61]. However, the presence of luorenone defects only may not
be suficient to produce the green band emission. The interchain
interactions and cross-linking of the polymers are also proposed
to be required for the appearance of the green band [62]. These
defects can easily be produced during synthesis and functioning
of the device. The emission of the device suggested that the carrier
recombination takes place in the PFO/ZnO NRs interface as recently
reported [63]. The interaction between the ZnO NRs surface and
PFO molecules makes the PFO link up with ZnO. This leads to PFO/
ZnO interface producing a strong defect emission [64]. As a result,
the device exhibits a broad EL spectrum in the range 415 nm to
630 nm and gives the cold white light as shown in Fig. 6.8a. The color
quality of the printed LED was investigated with the Commission
International DE L´Eclairage (CIE) as shown in Fig. 6.8b. The
resultant light has a cold white impression (bluish) with color
coordinate: x = 0.2574 and y = 0.3961 and a correlated color
temperature (CCT) of 8367 K.
Using the same low-temperature chemical growth method
described above, ZnO nanorods grown on paper substrate were also
used as piezoelectric elements to harvest energy from mechanical
movements. The word piezoelectricity means “electricity by
pressure” and is derived from the Greek “piezin,” which means
“to press” or “squeeze” and the term “piezoelectric” may have
been deined considering the direct piezoelectric effect of certain
materials or we can say that piezoelectricity is a form of electricity
created when certain crystals are bent or otherwise deformed.
The piezoelectric effect, according to the original deinition of
the phenomenon was irst announced during the session of the

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