Room-Temperature, Ultrafast, and Aqueous-Phase Synthesis of Ultrasmall LaPO4:Ce3+, Tb3+ Nanoparticles with a Photoluminescence Quantum Yield of 74%

LaPO₄:Ce³⁺, Tb³⁺ nanoparticles with a particle size of 2.7 nm are prepared by a facile room-temperature ligand-assisted coprecipitation method in an aqueous solution. Short-chain butyric acid and butylamine are used as binary ligands and play a critically important role in the synthesis of highly luminescent LaPO₄:Ce³⁺, Tb³⁺ nanoparticles. The absolute photoluminescence quantum yield as high as 74% can be achieved for extremely small LaPO₄:Ce³⁺, Tb³⁺ nanoparticles with an optimal composition of La_0.4PO₄:Ce_0.1³⁺, Tb_0.5³⁺, which is different from La_0.4PO₄:Ce_0.45³⁺, Tb_0.15³⁺ for bulk phosphor. The energy transfer from Ce³⁺ ions to Tb³⁺ ions is investigated in sub-3 nm LaPO₄:Ce³⁺, Tb³⁺ nanoparticles, and Ce³⁺ ion emission is almost completely suppressed. This room-temperature, ultrafast, and aqueous-phase synthetic strategy is particularly suitable for the large-scale preparation of highly luminescent LaPO₄:Ce³⁺, Tb³⁺ nanoparticles. LaPO₄:Ce³⁺, Tb³⁺ nanoparticles (110 g) can be synthesized in one batch, which is perfectly suited to the needs of industrial production.