Morphology and Crystallinity Tuned Luminescent Properties of Lanthanide-Doped YPO₄ Nanoparticles via a Facile Room-Temperature Synthesis

Abstract

Luminescent lanthanide-doped nanoparticles are conventionally synthesised under high-temperature conditions with extended reaction times. Here, lanthanide-doped YPO₄ nanoparticles were synthesised at room temperature by a facile coprecipitation method using sodium dodecyl sulphate (SDS) and citric acid (CA) as capping ligands to control morphology, crystallinity, and luminescence. Uncapped YPO₄:Tb³⁺ formed nanorod-like particles with a low quantum yield (~1%), whereas ligand capping produced ultrafine polycrystalline nanoparticles. pXRD, HRTEM, and SAED analyses indicate that the particles consist of nanocrystalline domains embedded within an amorphous matrix, favouring surface-defect-mediated nonradiative decay. SDS capping led to a modest increase in quantum yield (~7%), while stronger coordination by CA significantly enhanced nanocrystallite order, suppressed non-radiative losses, and increased the quantum yield to ~17%. Improved crystallinity further promoted efficient Tb³⁺→Eu³⁺ energy transfer in co-doped systems, with ligand-induced modulation of the local Eu³⁺ coordination environment influencing emission colour. Finally, red-and yellow-emitting nanoparticles were synthesised through the incorporation of single and mixed lanthanide dopants, demonstrating effective colour tunability in the nanoparticles.