  Relaxometry schemes employing nitrogen-vacancy (NV) centers in diamonds are
essential in biology and physics to detect a reduction of the color centers'
characteristic spin relaxation ($T_1$) time caused by, e.g., paramagnetic
molecules in proximity. However, while only the negatively-charged NV center is
to be probed in these pulsed-laser measurements, an inevitable consequence of
the laser excitation is the conversion to the neutrally-charged NV state,
interfering with the result for the negatively-charged NV centers' $T_1$ time
or even dominating the response signal. In this work, we perform relaxometry
measurements on an NV ensemble in nanodiamond combining a $520\,$nm excitation
laser and microwave excitation while simultaneously recording the fluorescence
signals of both charge states via independent beam paths. Correlating the
fluorescence intensity ratios to the fluorescence spectra at each laser power,
we monitor the ratios of both charge states during the $T_1$-time measurement
and systematically disclose the excitation-power-dependent charge conversion.
Even at laser intensities below saturation, we observe charge conversion, while
at higher intensities, charge conversion outweighs spin relaxation. These
results underline the necessity of low excitation power and fluorescence
normalization before the relaxation time to accurately determine the $T_1$ time
and characterize paramagnetic species close to the sensing diamond.
