Novel Orange-Emitting YPO₄:Sm³⁺/Polymer Nanocomposite Phosphor Films for LED Applications

A polymer based nanocomposite (NC) material embedded with highly luminescent nanopowders could be promising for replacing traditional luminescent materials from a technological point of view. In this study, we have successfully obtained YPO₄: Sm³⁺ /Polymer nanocomposite phosphor films by embedding YPO₄: Sm³⁺ luminescent nanoparticles (NPs) for orange-light emitting diode (LED) applications. These luminescent NPs were synthesized using the sol gel method in different polymer matrices i.e. polystyrene (PS) and poly (methyl methacrylate) (PMMA) by using direct solution mixing. The structural, morphological, and photoluminescence characteristics of the nano-phosphors and resulting NC films were examined and discussed. The emission spectra of YPO₄: Sm³⁺ (x at.%) nano-phosphors under near-UV excitation at 404 nm were dominated by orange emission attributed to ⁶H_5/2 $\to$   ⁴F_7/2 (601 nm) luminescence of Sm³⁺ ions. The optimum doping concentration of activator Sm³⁺ in YPO₄ matrix was found to be 5 at.%. When the doping concentration of Sm³⁺ was higher than 5 at.%, concentration quenching occurred. The incorporation of YPO₄: Sm³⁺ NPs into polymer matrices indicated that the NCs retained the original luminescence properties of the luminescent NPs, although a decrease in their emission intensity was observed for the NC films, attributable to a polymer matrix effect, which dominated in PS matrix. The fluorescence decay times of NPs in the NC films were measured and compared to those of proper YPO₄: Sm³⁺ nano-phosphors. A decrease in decay time in NC film was observed due the effective refractive index effect. Temperature-dependent photoluminescence (TDPL) of PMMA NC film was studied in 100-400 K range, investigating the thermal stability of the film. Additionally, CIE coordinates confirmed the red-orange light emission of the prepared phosphors and NC films. The obtained results indicate that the synthesized polymer-nanophosphor NC films are promising candidates for orange-LED applications.