Quantification of Alkali‐Fluoride Nanoparticle Dissolution in Aqueous Media as a Function of Crystallinity and Surface Modification

Time‐resolved fluoride release from alkali‐fluoride nanoparticles in water is quantified to decouple lattice‐intrinsic from surface‐mediated effects on dissolution. Bare and coated and particles are examined under fixed matrix conditions using a dialysis‐coupled fluoride ion‐selective electrode (‐ISE). Dissolution kinetics are fitted with a speciation‐aware model to extract activity‐based solubility constant and an effective rate constant ; TEM, DLS, and ICP‐OES provide morphological and mass‐related confirmation. dissolves faster and reaches higher fluoride plateaus than , despite the lower bulk solubility product of LiF, consistent with facet/morphology‐controlled reactivity. Fits yield a quartz‐like dependence on undersaturation for but indicate inhibition/passivation near equilibrium for . Surface chemistry primarily suppresses rates: mesoporous silica reduces by about an order of magnitude with little change in plateau concentration; poly(acrylic acid) decreases for both lattices and lowers the plateau for ; an amphiphilic polymer causes moderate suppression and shows localized notch etching at coating vacancies. Joint reporting of matrix‐specific apparent and activity‐based solubility enables cross‐comparison. The resulting lattice‐surface map provides design guidance for engineering lanthanide‐doped nanoparticles with predictable aqueous stability for imaging, sensing, and theranostic applications.