  We have characterized thermal susceptibilities of the spectral band at 740 nm
of silicon-vacancy (SiV) centers in Si- and Si,P-doped nanodiamonds over a
temperature range from 295 K to 350 K, which is of interest for thermometry in
biological systems. Si-doped crystals reveal linear dependence of the SiV
zero-phonon line position, width and relative amplitude with susceptibilities
of 0.0126(4) nm/K, 0.062(2) nm/K and $-0.037(2)$ K$^{-1}$, respectively.
Si,P-doped nanodiamonds show significantly smaller (up to 35 % for the width)
susceptibilities and prove control of SiV properties with additional chemical
doping. It is argued that a significant contribution to the heating of the
nanodiamonds induced by laser light can be intrinsic due to a high
concentration and low luminescence quantum yield of SiV centers.
