Fluorescent Silica Nanoparticles Through Silica Densification

A method for producing core-shell silica nanoparticles comprising the steps of:

• a) preparing a silica core by combining a silica precursor and a silica precursor covalently bound to a light-absorbing material and/or light-emitting fluorescent or phosphorescent material under conditions such that the silica precursors are hydrolyzed resulting in formation of a silica core, wherein the light-emitting material and/or light-absorbing material is covalently bound to the silica network of the core;
• b) forming a silica shell encapsulating the silica core by adding a silica precursor at temperatures below 50° C., under conditions such that formation of new silica nanoparticles is not observed;
• and
• c) subjecting the core-shell silica nanoparticles from step b) to a temperature of 50 to 100° C. over a period of at least 12 hours and/or pressure of at least 1.1 atmospheres.

A core-shell nanoparticle comprising:

• a) a core comprising silica and a light-emitting fluorescent or phosphorescent material and/or a light-absorbing material, wherein the light-emitting and/or light-absorbing material is covalently bound to the silica network of the core, and wherein the longest dimension of the core is 5 to 500 nm;
• and
• b) a shell comprising silica, wherein the longest dimension of the core-shell nanoparticle is 5 to 500 nm,
• wherein the density of the core-shell nanoparticle is at least 1.4 g/cm3.