Effect of Pr3+ concentration in luminescence properties & upconversion mechanism of triple doped NaYF4: Yb3+, Er3+, Pr3+

Lanthanide-doped fluoride nanocrystals (NCs) exhibit excellent optical features, including upconversion and downconversion luminescence (UCL and DCL), that can be utilized in a variety of applications. In this study, we have successfully demonstrated the photoluminescence behavior of triple-doped NaYF4: Yb3+, Er3+, Pr3+ NCs in the Vis-NIR region. Herein, highly monodisperse hexagonal phase NaYF4: Yb0.2, Er0.02, Prx nanocrystals in various Pr3+ (x = 0, 0.1, 0.5, and 1 mol %) concentration with ∼22 nm diameter synthesized by thermal decomposition technique. The photoluminescence studies for all samples were performed under 980 nm laser excitation. The luminescence intensity of Er3+ including blue (407 nm), green (520 and 540 nm), red (654 nm), and near-infrared (845 nm and 1530 nm) emissions was significantly quenched and Pr3+ emission intensity at 1290 nm (Pr3+:1G4→3H5) changes irregularly upon doping with Pr3+ ions. Furthermore, we performed the excitation power dependence and decay time analysis to investigate the energy transfer and upconversion mechanisms of samples. These findings indicate that the presence of praseodymium strongly reduces emission intensities due to abundant cross-relaxation channels. In addition, particle size is an efficient factor, shedding light on the influence of Pr3+ on the energy transfer and upconversion mechanisms of the fluorides

Boosting NIR emission through Yb concentration optimization in active-core/active shell upconversion nanocrystals

Here in, we report a new strategy to achieve a strong emission in the NIR region, especially in ∼802 nm, by introducing a core-shell structured UCNPs, denoted as NaYF4: 25%Yb3+, 0.5%Tm3+@NaYF4: x%Yb3+ (x = 0, 2, 5,15,100), offering a superior advantage for future biosensing-bioimaging application. Through the induction of specific Yb3+ ion concentrations (2 % and 5 %) into the shell, under 980 nm laser excitation, we noticed a selective reduction in emission peaks in the visible region with an intensified NIR (802 nm). To evaluate the results, the NIR/visible ratio was examined by increasing the Yb3+ dopant concentration in the shell, and the highest ratio was observed for NIR/red emission (NIR/646 nm) increasing from 38 (0%Yb3+). 62 (5%Yb3+) and 40.9 (15%Yb3+) indicate greater attenuation of the emission at 646 nm compared to 449 nm, and 473 nm. Decay time and power dependence analysis studied on the optimum nano crystals outcomes (NaYF4: 25%Yb3+,0.5%Tm3+@ NaYF4: x%Yb3+ (x = 0, 2, 5). The results highlighted a significant increase in decay time at the 3H4 → 3H6 state of Tm3+ ions in line with the enhancement of 802 nm emission. The power dependence analysis for the NIR (802 nm), the slope values obtained as 2.03 (core) to 1.68 (0%Yb), 2.01(2%Yb), 1.76 (5%Yb) and 1.97 (15%Yb), indicating the two-photon process is responsible upconversion process. These findings provide evidence that either decay time or power dependence studies align with the enhancement of 802 nm emission

Upconversion nanoparticles-based targeted imaging of MCF-7 breast cancer cells

Upconversion nanoparticles (UCNPs) doped with lanthanides are introduced as a significant tool in bioimaging applications. Here in, a comparative study has been performed to understand the cell internalization capacity of folic acid (FA) and arginine-glycine-aspartic acid-lysine (RGDK) ligands. To achieve this goal, polyacrylic acid (PAA) coated UCNPs (NaYF4:Yb3+, Er3+) are conjugated with various surface ligands such as FA and RGDK through a straightforward ligand exchange procedure. Ligand conjugation to UCNPs was characterized with a transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) spectroscopy, zeta potential measurements, nuclear magnetic resonance (NMR) spectroscopy, and NanoDrop measurements. The cellular uptake of the nanoparticles was investigated on the breast cancer MCF-7 cell line. The obtained results demonstrated that folic acid and RGDK functionalized UCNPs showed remarkably higher cellular uptake, which clearly indicates that the specific targeting of UCNPs provides a better quality of sub-cellular imaging at lower energy band region