NIR emitting GdVO4:Nd nanoparticles for bioimaging: the role of the synthetic pathway

Nd-doped GdVO4 (GdVO4:Nd) represents a promising candidate among near-infrared emitting nano particles (NPs) for time-gated bioimaging owing to its non-damaging, non-heating excitation wavelength provided by cheap lasers. The GdVO4:Nd synthesis should guarantee a precise control over NPs dimensions along with optimized luminescence properties. Here, we carried out for the first time a systematic study of GdVO4:Nd NPs synthetic routes: a simple co-precipitation was compared to colloidal, reverse micelles and sonochemical methods. The NPs were characterized for their structural, morphological, spectral and minescence lifetime properties, also with respect to a micrometric reference prepared by solid state action. All the prepared NPs showed high crystallinity, with spindle-like morphology and dimensions smaller than 150 nm. The synthetic procedure plays a crucial role on the sample purity and crystallite size, leading to notable differences in emission intensity and luminescence decay. The co-precipitation and colloidal syntheses led to particles with suitable morphology and high emission intensity. The optimal dopant content was found to be close to 2%, in order to avoid concentration quenching effects. Luminescence decay lifetimes of nanosized samples are long enough to counter tissue autofluorescence in time-gated applications.