Coated up-conversion nanoparticles

A method of whole-body imaging of an animal, comprising:

• administering to the animal a biocompatible upconversion nanoparticle comprising:
• a core of cubic nanocrystals comprising α-Na (Y, Yb, Tm)F4;
• and
• an epitaxial shell formed from CaF2,
• wherein the molar ratio of Tm/(Y+Yb+Tm) is a about 0.5±0.02%, and the molar ratio of Yb/(Y+Yb+Tm) is greater than 30%;
• exciting the nanoparticle with a laser a wavelength in the range of about 900 nm to about 1064 nm;
• and
• recording the emission luminescence at a wavelength in the range of about 980 nm to about 800 nm.

A method for activating a light sensitive molecule, comprising:

• administering to a cell an upconversion nanoparticle coated with a light sensitive molecule;
• exciting the nanoparticle with a laser having a wavelength from about 900 nm to about 1064 nm;
• causing the particle to emit a luminescence at a wavelength of from about 340 nm to about 380 nm;
• and
• activating the light sensitive molecule.