Bi3+ ion doping: An effective strategy to significantly enhance luminescence performances of NaGdF4: Eu3+ red-emitting nanocrystals

Abstract A series of NaGd(0.99-x%)F4: 1% Bi3+, x% Eu3+ (x = 0–50) and NaGd(1-x%)F4: x% Eu3+ (x = 0–50) nanocrystals (denoted as NGBF-x% Eu3+ and NGF-x% Eu3+, respectively) have been synthesized by hydrothermal method. The influence of Bi3+ and Eu3+ on microstructures and luminescence properties of the products are deeply investigated. The TEM results display that all the obtained products are irregular polyhedrons with a diameter in a range from 30 to 80 nm with the increasing substitution concentration of Eu3+. It was found that the introduction of Bi3+ hardly affects the morphology and size of the obtained products. Under the excitation of 393 nm NUV, all samples exhibit the typical emission of Eu3+ ions with main red and yellow emissions centered at 616 and 591 nm, respectively. After doping a small amount of Bi3+ ions, the largest emission intensity of the characteristic emissions of Eu3+ for the gained NGBF-x% Eu3+ nanocrystals appeared at x = 0.2, whereas it observed at x = 0.3 for the obtained NGF-x% Eu3+ nanocrystals. It is obviously that the introduction of 1% Bi3+ ions not only increases the emission intensity of Eu3+ ions significantly, but also reduces the doping concentration of Eu3+. Especially, studied NGBF-20% Eu3+ phosphor exhibits excellent stand up to thermal impact during thermal cycling between 298 and 473 K. A WLED device by merging a NUV chip, NGBF-20% Eu3+ phosphor and commercial (Sr,Ba)2SiO4: Eu2+ green phosphor/BaMgAl10O17: Eu2+ blue phosphor possesses suitable correlated color temperature (CCT, 7395 K) and high color rendering index (CRI, 90.8%). These results unambiguously show that the NGBF-x%Eu3+ nanocrystals are promising candidate for applications in WLEDs.