<p>Boron-doped silicon nanocrystals (Si NCs) with localized surface plasmon resonance (LSPR) have been obtained via postsynthetic diffusion doping with the use of volatile BBr₃ and BCl₃ precursors. This method decouples nanocrystal growth from impurity introduction, allowing precise control over the doping process while preserving the initial Si NC dispersity. Inductively coupled plasma mass spectrometry (ICP-MS) analysis reveals a high total boron concentration (up to 17 at. %), predominantly located at the particles’ surface layers, with only up to ~ 2.5 at. % located in the core. Carrier concentrations up to 1.4·10²⁰ cm⁻³ (0.28 at. %) are calculated from localized surface plasmon resonance in the IR region. Rapid thermal annealing (RTA) has proved effective in breaking up clusters, significantly increasing the active carrier concentration and blueshifting the LSPR peak. The effective boron diffusion coefficient in Si NCs at 660 °C is estimated at ~ 10^–18 cm²·s⁻¹. The work demonstrates a controllable route to plasmonic p-type Si NCs and underlines RTA as a key step for improving their electrical activation after doping.</p>