Enhanced hydrothermal crystallization and color tailorable photoluminescence of hexagonal structured YPO4:Sm/Tb nanorods

Abstract

Hexagonal structured YPO₄:Tb/Sm (h-YPO₄:Tb/Sm) nanorods with significantly large aspect ratios of up to ∼32 have been successfully fabricated via hydrothermal crystallization in the presence of sodium malate (Mal²⁻) and superfluous PO₄³⁻. The combined techniques of XRD, SEM, TEM, and PLE/PL were employed to characterize the products, and the formation mechanism of the nanorods was discussed in detail. It was found that Mal²⁻ and superfluous PO₄³⁻ jointly ensured the crystallization of the metastable hexagonal phase, and the latter promoted the 1D growth of the crystals. The h-(Y_0.99−xTb_0.01Sm_x)PO₄ ternary phosphors simultaneously displayed the green emission of Tb³⁺ at 545 nm and the red emission of Sm³⁺ at 601 nm under 221 nm UV excitation, with which the emission color was finely tuned from green to yellow by increasing the Sm³⁺ content. The Tb³⁺ → Sm³⁺ energy transfer in h-(Y_0.99−xTb_0.01Sm_x)PO₄ was revealed to occur via an electric dipole–dipole interaction mechanism. The fluorescence lifetime of Tb³⁺ was found to steadily decrease with increasing Sm³⁺ concentration, and the efficiency of energy transfer was determined to be ∼31.2% at the optimal Sm³⁺ content of 4 at% (x = 0.04).