9 Si Nanopowder for Photoluminescence and Hydrogen Generation Materials
363
Fig. 9.13 PL excitation spectra for blue-PL Si nanopowder in hexane observed at various PL
energies between 2.21 and 3.65 eV
Figure 9.13 shows the PL excitation spectra for blue-PL Si nanopowder in
hexane. The excitation spectra are measured by scanning the incident photon energy
with the PL energy fixed, and thus, they correspond to absorption which causes PL
emission at the fixed PL energy. For the PL energies between 2.39 and 2.93 eV, i.e.,
transitions from the vibrational ground-state, peaked structure is observed, showing
that absorption by adsorbed DMA causes the PL peaks. In the higher energy region,
on the other hand, broad structure is present with no vibronic bands. The broad
structure is attributable to absorption by Si nanopowder, indicating that the PL peaks
with energies higher than the (0,0) peak result from band-to-band excitation of Si
nanopoweder.
Figure 9.14 shows the time-dependent PL intensity measured at 2.91 eV (curve a)
and 3.35 eV (curve b). The PL intensity at 3.35 eV for DMA without Si nanopowder
is shown in curve c for reference, and in this case, the PL lifetime is determined to
be 5.0 ns. The PL lifetime measured at 2.91 eV which corresponds to the (0, 1)
transition of DMA, on the other hand, is much shorter, i.e., 0.97 ns. Considering
that the pulse width of incident light is 0.75 ns, the real lifetime is estimated to be
0.62 ns for DMA with Si nanopowder and 4.9 ns for DMA without Si nanopowder.
The short lifetime results from the high PL transition probability, indicating that
the interaction of DMA with Si nanopowder greatly increases the PL transition
probability.
The PL energy for curve b (3.35 eV) corresponds to the (n+1, n) PL band
overlapped with the more intense band-to-band transition of Si nanopowder. The
lifetime considering the pulse width is estimated to be 3.1 ns, indicating that the
lifetime of electron-hole pairs in Si nanopowder is much longer than the PL lifetime
arising from adsorbed DMA of 0.62 ns.
363
Fig. 9.13 PL excitation spectra for blue-PL Si nanopowder in hexane observed at various PL
energies between 2.21 and 3.65 eV
Figure 9.13 shows the PL excitation spectra for blue-PL Si nanopowder in
hexane. The excitation spectra are measured by scanning the incident photon energy
with the PL energy fixed, and thus, they correspond to absorption which causes PL
emission at the fixed PL energy. For the PL energies between 2.39 and 2.93 eV, i.e.,
transitions from the vibrational ground-state, peaked structure is observed, showing
that absorption by adsorbed DMA causes the PL peaks. In the higher energy region,
on the other hand, broad structure is present with no vibronic bands. The broad
structure is attributable to absorption by Si nanopowder, indicating that the PL peaks
with energies higher than the (0,0) peak result from band-to-band excitation of Si
nanopoweder.
Figure 9.14 shows the time-dependent PL intensity measured at 2.91 eV (curve a)
and 3.35 eV (curve b). The PL intensity at 3.35 eV for DMA without Si nanopowder
is shown in curve c for reference, and in this case, the PL lifetime is determined to
be 5.0 ns. The PL lifetime measured at 2.91 eV which corresponds to the (0, 1)
transition of DMA, on the other hand, is much shorter, i.e., 0.97 ns. Considering
that the pulse width of incident light is 0.75 ns, the real lifetime is estimated to be
0.62 ns for DMA with Si nanopowder and 4.9 ns for DMA without Si nanopowder.
The short lifetime results from the high PL transition probability, indicating that
the interaction of DMA with Si nanopowder greatly increases the PL transition
probability.
The PL energy for curve b (3.35 eV) corresponds to the (n+1, n) PL band
overlapped with the more intense band-to-band transition of Si nanopowder. The
lifetime considering the pulse width is estimated to be 3.1 ns, indicating that the
lifetime of electron-hole pairs in Si nanopowder is much longer than the PL lifetime
arising from adsorbed DMA of 0.62 ns.