Optical properties of In2O3 nanoparticles coated with polyvinyl-alcohol (PVA) are studied. Compared with uncoated
In2O3 nanoparticles, PVA coated sample show enhanced UV-blue emission and suppressed parasitic green emission.
Ultraviolet (UV)-blue photodetectors were then fabricated by depositing aluminum (Al) as contacts on top of PVA
coated and uncoated samples. The photodetector with PVA coating, exhibits lower dark current and higher responsivity
than the photodetector without PVA coating. The rise and fall time of the PVA coated photodetector is about 500 s and
1600 s respectively, one half of the uncoated device. These improvements are attributed to surface passivation of In2O3
nanoparticles by PVA, which reduces the surface defects density and increase free carrier concentration of In2O3
Light emitting diodes (LEDs) are excellent candidates for the applications requiring low noise light sources with wavelengths ranging from 200 nm to 900 nm. These applications include the detection of fluorescence from protein molecules excited with the ultraviolet (UV) light (200-300nm) for identifying miniscule amounts of hazardous biological pathogens. The detection system including the light source must exhibit low noise and high stability over tens of minutes. In comparison with xenon, tungsten halogen lamps, lasers, and other conventional UV sources, UV LEDs are more stable, have lower noise, are smaller, cheaper, and easier to use. We report on the low frequency fluctuations of the current and light intensity of LEDs (fabricated by SET, Inc.) with wavelengths ranging from 265nm to 340nm. The results are compared with the noise properties of the halogen lamps and other commercially available LEDs with the wavelengths of 375nm, 505nm and 740nm. We show that the LEDs fabricated by Sensor Electronic technology, Inc. are suitable for studying steady state and time-varying UV fluorescence of biological materials. The correlation coefficient between the current and light intensity fluctuations varies with the LED current and load resistance. This dependence is explained in terms of the contributions to the 1/f noise from the active region and from the LED series resistance. The noise level could be reduced by operating the LEDs at a certain optimum current level and by using a large external series resistance (in the current source driving mode).