Crystal structure, optical spectroscopy and energy transfer properties in NaZnPO4:Ce3+, Tb3+ phosphors for UV-based LEDs

Abstract

A new series of Ce³⁺, Tb³⁺ singly doped and Ce³⁺/Tb³⁺ co-doped NaZnPO₄ (NZPO) phosphors have been synthesized via a high-temperature solid-state reaction method at 800 °C. The crystal cell structure, luminescence proprieties, energy transfer, and chromaticity coordinates of the as-prepared phosphors were investigated in detail. The photoluminescence spectra of NZPO:Ce³⁺ phosphors exhibited broad emission in the 300–380 nm range, while under UV excitation, the singly doped NZPO:Tb³⁺ phosphor showed emission peaks at ∼485–690 nm among which the green emission peak appears at ∼543 nm. The Tb³⁺ green emission was significantly enhanced almost 20 times via energy transfer from Ce³⁺ to Tb³⁺. The energy transfer (ET) mechanism from Ce³⁺ to Tb³⁺ in NZPO is identified to be a resonant type via the dipole–dipole interaction mechanism with an ET efficiency of 91%. Intense green emission is obtained at very low Tb³⁺ concentrations under 285 nm excitation, making NZPO:Ce³⁺/Tb³⁺ an efficient UV-excited green phosphor. The NaZnPO₄:Ce³⁺/Tb³⁺ phosphors are promising UV convertible materials of green light for UV -LEDs applications.