Disclosed are luminescent compositions having luminescent particles coated by a surface capping agent. Luminescent particles include rare earth doped phosphors, semiconductor quantum dots, and organic phosphors. Surfactants include macromolecules, polypeptides, polysaccharides, and polymers. Rare earth doped phosphors have host compositions and rare earth dopants, wherein the host compositions include NaYF4, LaF3, YF3, CeF3, CaF2, CsCdBr3, and Y2O3, and wherein the rare earth dopants include Cs, Pr, Nd, Sm, Er, Gs, Tb, Dy, Ho, Er, Tim, Yb, and combinations of two or more of these. The refractive index mismatch of the luminescent compositions and surrounding medium is less than about 0.1. Also disclosed are methods of making the luminescent compositions, luminescent devices and displays containing the luminescent compositions, uses of the luminescent compositions in particle imaging velocimetry, and uses of the luminescent compositions as contrast agents for disease monitoring.