NIR Luminescence Enhancement of YVO:Nd Phosphor for Biological Application.

This work reports two systematic studies related to yttrium vanadate (YVO) phosphors. The first evaluates how the annealing temperature and V/Y molar ratio determine the emergence of a single YVO tetragonal phase, whereas the second concerns the optimal Nd concentration to improve the infrared emission properties for bio-labelling applications. The YVO:Nd phosphors were synthesized by adapting the non-hydrolytic sol-gel route. For the first study, samples containing different V/Y molar ratios (1.02, 1.48, 1.71, or 3.13) were obtained. For the second study, YVO:Nd phosphors containing different Nd concentrations (1.0, 3.0, 5.0, or 10.0% in mol) were prepared. X-ray diffractometry and RAMAN spectroscopy results revealed that, regardless of the heat-treatment temperature, the V/Y molar ratio of 1.48 was the best composition to avoid undesired phases like YO and VO. Photoluminescence results indicated that the sample containing 3.0% in mol of Nd and annealed at 1000 °C presented the best infrared emission properties. This sample displayed an intense broad band in the ultraviolet region, which was ascribed to the VO charge transfer band, as well as several bands in the visible and infrared regions, which were attributed to the Nd intraconfigurational f-f transitions. Regardless of the excitation wavelength (ultraviolet, visible, or near-infrared), the mean radiative lifetime was about 12.00 µs. The prepared phosphors presented absorption and emission bands in the biological window (BW) regions, which are located between 750 and 900 nm and between 1000 and 1300 nm, so they are candidates for applications in medical imaging and diagnoses.