Raman
scattering investigations of the diamond peak properties
of nanodiamonds with a size of 25 nm were performed in terms of temperature
and laser power dependency. A similar trend of a bathochromic shift
with increasing temperature and laser power was found, indicating
the optical induced heating mechanism to be one of the main influencing
factors on the Raman scattering behavior of nanodiamonds. As a direct
consequence, nanodiamond particle impurities such as graphite have
an indirect influence on the diamond peak properties by means of enhanced
optical absorption of the particle, resulting in a higher rate of
photoinduced heating. The results presented here are not only supplementing
the list of influencing factors on the Raman scattering properties
of nanodiamonds, but they also demonstrate that even a low graphite
content leads to local particle temperature differences in the range
of hundreds of °C already at low laser intensities within the
range 105 W/cm2 with a substantial effect on the Raman spectrum of the nanodiamonds.
This effect needs to be considered in numerous potential applications
utilizing nanodiamonds as sensors.
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