Effect of Pr<SUP>3+</SUP> concentration in luminescence properties & upconversion mechanism of triple doped NaYF₄: Yb<SUP>3+</SUP>, Er<SUP>3+</SUP>, Pr<SUP>3+</SUP>

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: Yb-0.2, Er-0.02, Pr(x)nanocrystals in various Pr3+(x = 0, 0.1, 0.5, and 1 mol %) concentration with similar to 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 Er(3+)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 Pr(3+)emission intensity at 1290 nm (Pr3+:(1)G(4)-> H-3(5)) changes irregularly upon doping with Pr(3+)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 Pr(3+)on the energy transfer and upconversion mechanisms of the fluorides.