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The neutral nitrogen‐vacancy (NV0) defects in diamond are photostable color centers, suitable for a wide range of applications in science and engineering. However, the photophysical properties of the centers have not yet been fully characterized. This work measured the stimulated emission cross sections of NV0in a single‐crystal diamond by two‐photon excitation of its matrix at 344 nm. From the measured photoluminescence spectrum and the fluorescence lifetime of 20 ± 1 ns, we determined a peak stimulated emission cross section of 1.43 ± 0.07 × 10−17cm2at 650 nm for the NV0centers. In addition, we have also examined the thermal shifts of the zero‐phonon line of NV0centers in nanoscale diamonds (~100 nm in diameter) over the temperature range of 30–120°C. A temperature measurement sensitivity of 0.2 K·Hz−1/2was achieved, which is about two‐fold better than that of NV−, despite that the fluorescence intensity of NV0is about six‐fold lower than that of NV−in the same nanoparticles. The result is attributed to the smaller electron–phonon coupling strength of the neutral center, compared with its negatively charged counterpart. Photoluminescence of NV0centers in diamonds is measured upon two‐photon ultraviolet excitation. The fluorescence lifetimes and stimulated emission cross sections are quantified. The thermal shifts and intensity changes of the zero‐phonon line upon green laser excitation are also evaluated.