Synthesis of Highly Luminescent Silica-Coated Upconversion Nanoparticles from Lanthanide Oxides or Nitrates Using Co-Precipitation and Sol–Gel Methods

Abstract

Upconversion nanoparticles (UCNPs) are under consideration for their use as bioimaging probes with enhanced optical performance for real time follow-up under non-invasive conditions. Photostable and core-shell NaYF4:Yb3+, Er3+-SiO2 UCNPs obtained by a novel and simple co-precipitation method from lanthanide nitrates or oxides were herein synthesized for the first time. The sol–gel Stöber method followed by oven or supercritical gel drying was used to confer biocompatible surface properties to UCNPs by the formation of an ultrathin silica coating. Upconversion (UC) spectra were studied to evaluate the fluorescence of UCNPs upon red/near infrared (NIR) irradiation. ζ-potential measurements, TEM analyses, XRD patterns and long-term physicochemical stability were also assessed and confirmed that the UCNPs co-precipitation synthesis is a shape- and phase-controlling approach. The bio- and hemocompatibility of the UCNPs formulation with the highest fluorescence intensity was evaluated with murine fibroblasts and human blood, respectively, and provided excellent results that endorse the efficacy of the silica gel coating. The herein synthesized UCNPs can be regarded as efficient fluorescent probes for bioimaging purposes with the high luminescence, physicochemical stability and biocompatibility required for biomedical applications.

The Influence of Concentrations of Sensitizers and Activators on Luminescence Kinetics Parameters of Up-Conversion Nanocomplexes NaYF4:Yb3+/Tm3+

“…Excitation in the near-infrared range, located in the transparency region, opens up wide opportunities for biovisualization and sensorics of various processes occurring in living cells. In addition, up-conversion luminophores are used for hidden protective marking [5], in photovoltaic devices [6], as fluorescent markers and drug carriers in biomedical applications [7][8][9][10][11][12][13], in thermosensors [14,15], in vacuum measurement [16], for the increase in the efficiency of solar panels [17,18], in laser cooling [19], in photoelectrochemical bioanalysis [13] and in up-conversion lasers [20].…”

“…One of the most effective matrices for doping are nanopowders with a crystal structure of the gagarinite type based on NaYF 4 [25] and NaGdF 4 [26]. The NaYF 4 matrix is actively used for biological tissue structure visualization and photodynamic therapy [10][11][12][13].…”

“…Photonics 2024, 11,228 2 of 14 consecutive transfer of excitation energy, cross-relaxation up-conversion, cooperative sensitization and cooperative luminescence [24]. The scheme of the electronic levels of the sensitizer (ytterbium) and activator (thulium) and the mechanisms of excitation transmission are shown in Figure 1.…”