Core/shell-type nanorods of Tb3+-doped LaPO4, modified with amine groups, revealing reduced cytotoxicity

Nanoparticles revealing interesting and useful properties such as luminescence, magnetism, biocompatibility, high-capacity carriers (e.g., drug delivery), resistance for photo-bleaching and thermal-degradation, plasmonic effects, and other optoelectronic properties have been intensively studied over the last decade and their synthesis has been aimed by many researchers (Wang et al. 2010a ; Grzyb et al. 2012 ; Limaye et al. 2011 ; Yang et al. 2009 ; Corr et al. 2008 ; Warren and Chan 2009 ; Park et al. 2010 ; Barnes et al. 2003 ; Zhang et al. 2009 ). In this group of nanostructures, nanophosphors doped with lanthanide ions exhibiting intensive luminescence, are materials of special importance (Grzyb et al. 2013a ). Most of such crystalline, inorganic phosphors are resistant to high temperature and UV irradiation. They also usually do not bleach over a long period of time and they can form stable aqueous colloids (Grzyb et al. 2012 ), which is very important for bio-applications (Nyk et al. 2008 ). The properties crucial for bio-applications are the small size, low-toxicity, and intensive luminescence. Lanthanide-doped nanophosphors and Q-dots show such properties. However, both classes of nanoparticles have certain benefits and drawbacks, e.g., some Q-dots based on heavy metals exhibit not only more efficient luminescence than the lanthanide-doped nanomaterials but also higher cytotoxicity (Xu et al. 2011 ; Gagné et al. 2008 ). There are many well-known inorganic phosphors based on lanthanide ions, e.g., simple fluorides, borates, vanadates, manganates, phosphates, and their complex analogs. Phosphates with the general formula: LnPO 4 or hydrated ones (LnPO 4 · n H 2 O) doped with activator ions (e.g., Eu 3+ , Tb 3+ , Tm 3+ ) can exhibit bright, multicolor luminescence dependent on their crystal structure, chemical composition and morphology (Yu et al. 2006 ; Phaomei et al. 2010 ; Phaomei et al. 2011 ); high refractive index and thermal stability (Ghosh et al. 2010 ; Blasse and Grabmaier 1994 ); biocompatibility, which are the well-known properties of many phosphate species (Hirsch et al. 2007 ). As the nanostructures discussed reveal such properties, the phosphates have been successfully applied fluorescent lamps, tracers, sensors and bio-sensors, contrast agents, drug carriers, and as other biocompatible species (Xu et al. 2011 ; Hölsä 2009 ; Kim 2000 ; Chander 2005 ; Shionoya and Yen 1999 ).