To establish highly luminescent nanoparticles for monitoring fluid flows, we examined the preparation of silica nanoparticles based on immobilization of a cyclometallated iridium(III) complex and an examination of the photophysical studies provided a good insight into the Ir(III) microenvironment in order to reveal the most suitable silica nanoparticles for micro-particle imaging velocimetry (μ-PIV) studies. Iridium complexes covalently incorporated at the surface of preformed silica nanoparticles, [Ir-4]@Si500-Z, using a fluorinated polymer during their preparation, demonstrated better stability than those without the polymer, [Ir-4]@Si500, an increase in steady state photoluminescence intensity (and therefore particle brightness) and lifetimes which are increased by seven-fold compared with nanoparticles with the same metal complex attached covalently throughout their core, [Ir-4]⊂Si500. Screening of the nanoparticles in fluid flows using epi-luminescence microscopy also confirm that the brightest, most suited particles for micro-particle imaging velocimetry (μ-PIV) measurements are those with the Ir(III) complex immobilised at the surface with fluoropolymer i.e. [Ir-4]@Si500-Z . μ-PIV studies demonstrate the suitability of these nanoparticles as nanotracers in microchannels.