Characterization Techniques in Nanotechnology …
29
1997). Two forms of photoluminescence are available; fluorescence and phosphorescence. Fluorescence involves de-excitation of a chemical substance by emitting
photons while transiting to its ground state. Some of the absorbed energy is dissipated, so that the emitted photons of light are of lower energy than those absorbed.
However, phosphorescence is a chemical transition in which the absorbed energy
undergoes intersystem crossing into a state with a different multiplicity of spin. The
lifetime of phosphorescence (10
−4 to 10
−2 s) is usually much longer than that of
fluorescence (10
−8 to 10
−4 s). The principle of photoluminescence system has been
described elsewhere (Harris 2010). A monochromator is used for selection of excitation wavelength, and luminescence is observed through the second monochromator
positioned at 90° to the incident light to minimize the intensity of scattered light
reaching the detector. If the excitation wavelength is fixed and the emitted radiation
is scanned, an emission spectrum is generated. The application of photoluminescence
for semiconductor material is depicted in Fig. 8.
The PL spectra of anatase TiO 2 nanoparticles, obtained with an excitation wavelength of 310 nm, are displayed in Fig. 9a. TiO 2 is an indirect band gap semiconductor
Fig. 8 Schematic diagram
of process in semiconductor
material (McNaught and
Wilkinson 1997)
Fig. 9 Photoluminescence spectra for a undoped and Mg-doped TiO 2 nanoparticles (Giahi et al.
2019), b ZnO nanopowder (Taunk et al. 2015)
29
1997). Two forms of photoluminescence are available; fluorescence and phosphorescence. Fluorescence involves de-excitation of a chemical substance by emitting
photons while transiting to its ground state. Some of the absorbed energy is dissipated, so that the emitted photons of light are of lower energy than those absorbed.
However, phosphorescence is a chemical transition in which the absorbed energy
undergoes intersystem crossing into a state with a different multiplicity of spin. The
lifetime of phosphorescence (10
−4 to 10
−2 s) is usually much longer than that of
fluorescence (10
−8 to 10
−4 s). The principle of photoluminescence system has been
described elsewhere (Harris 2010). A monochromator is used for selection of excitation wavelength, and luminescence is observed through the second monochromator
positioned at 90° to the incident light to minimize the intensity of scattered light
reaching the detector. If the excitation wavelength is fixed and the emitted radiation
is scanned, an emission spectrum is generated. The application of photoluminescence
for semiconductor material is depicted in Fig. 8.
The PL spectra of anatase TiO 2 nanoparticles, obtained with an excitation wavelength of 310 nm, are displayed in Fig. 9a. TiO 2 is an indirect band gap semiconductor
Fig. 8 Schematic diagram
of process in semiconductor
material (McNaught and
Wilkinson 1997)
Fig. 9 Photoluminescence spectra for a undoped and Mg-doped TiO 2 nanoparticles (Giahi et al.
2019), b ZnO nanopowder (Taunk et al. 2015)