Monolayer-stabilized nanoparticles of LaF3 and LaPO4 doped with the luminescent trivalent lanthanide ions Eu3+, Nd3+, Er3+, Pr3+, Ho3+, and Yb3+ have been prepared. These ions emit in the visible and in the near-infrared part of the electromagnetic spectrum. The ions Nd3+, Er3+ Pr3+, and Ho3+ are the main focus in this research because they show emissions in telecommunication windows. The Eu3+ ion is an excellent probe for the structural environment of the luminescent ion. It is shown that these lanthanide ions are incorporated in the inorganic host of the particles and that the particles are dispersable in organic solvents. The luminescent lifetimes of the ions are increased orders of magnitude compared to organic complexes, with values ranging from several microseconds for Pr3+ and Ho3+, up to about 200 μs for Nd3+, and 1 ms for Er3+. This increase in the luminescence lifetime is indicative of an effective shielding of the lanthanide ions from non-radiative decay of the excited state by the high-energy vibrations of the solvents and the coordinated organic ligands. A model is proposed to describe the non-exponential behavior of the lumienscence decay by quenching from outside the particle.