Ultrabright luminescent lanthanide nanoparticles comprising terbium, with longer excited-state lifetime

A luminescent lanthanide nanoparticle, comprising a lanthanide ion nanoparticle including terbium, and several molecules of chromophore ligand that are bonded to the surface of the lanthanide ion nanoparticle,

• wherein said lanthanide ion nanoparticle comprises terbium ions and ions of at least a second lanthanide selected from the group consisting of:
• cerium, praseodymium, neodymium, samarium, europium, dysprosium, holmium, erbium, thulium and ytterbium;
• said ligand is an organic molecule comprising at least one chromophore radical of formula I or of formula II:
• wherein R is selected from H, CN group or COOH group for formula I and wherein R is selected from CN group or COOH group for formula II,
• wherein the luminescent lanthanide nanoparticle has an excited-state lifetime and a brightness that are simultaneously superior to 3 ms and 104 M−1·cm−1 respectively.