Structural modulation induced intensity enhancement of full color spectra: a case of Ba3ZnTa2−xNbxO9:Eu3+ phosphors

Abstract

Modulation of structural order–disorder transition and structural oxygen defects can provide fundamental insights in the optimization of luminescence performances of phosphors. In this study, the luminescence of Ba₃ZnTa₂O₉ (BZT) was systematically elucidated, including the emission arising from the charge transfer (Nb⁵⁺/Ta⁵⁺ → O²⁻) and anti-site oxygen defect emission due to the B-site disordering (defect type: [2Zn_Nb³⁻ + 3V_o²⁺]), as corroborated by the electronic structural calculations and detailed experiments. We present a two-step design for the optimization of luminescence properties of Ba₃ZnTa₂O₉ phosphor. In the first step, the B-site equivalent doping (Ta⁵⁺ substituted by Nb⁵⁺) was used to modulate the B-site atomic arrangement, which induced the formation of the cubic phase with B-site full disordering. In the second step, the A-site nonequivalent doping (Ba²⁺ substituted by Eu³⁺) was used to decrease the oxygen defect concentration. After the two-step optimization, the photoluminescence excitation spectrum of Ba_3−yEu_yZnNb₂O₉ (y = 0.1) shows a broad band excitation (300–400 nm), which is a good match with the near-UV LED chip emission. Even more importantly, the emission spectrum covers the entire visible spectral region and exhibits a remarkably enhanced emission intensity (a 40 times enhancement when compared to that of the intrinsic BZT). The fabricated LED device comprising an n-UV chip (λ = 370 nm) and a single-component Ba_3−yEu_yZnNb₂O₉ (y = 0.1) phosphor coating emits a warm white light with a low correlated color temperature (CCT = 4813 K) and a good color rendering index (R_a = 82.36).