Spectral management and energy‐transfer mechanism of Eu³⁺‐doped β‐NaGdF₄:Yb³⁺,Er³⁺ microcrystals

Abstract

b-NaGdF 4 :Yb 3+ ,Er 3+ upconversion (UC) microcrystals were prepared by a facile hydrothermal process with the assistance of ethylene diamine tertraacetic acid (EDTA). The b-NaGdF 4 UC microcrystal morphology was controlled by changing the doses of EDTA and NaF. Uniform hexagonal structure can be obtained at the 2 mmol EDTA and 9-10 mmol NaF. The UC emissions of b-NaGdF 4 :Yb 3+ , Er 3+ microcrystals were tuned by the variation of Eu 3+ doping level (0%-5%), where the red/green intensity ratio decreased with the Eu 3+ concentration increase.It was found on the base of rate equations that with the Eu 3+ doping, the energy back transfer process 2 H 11/2 / 4 S 3/2 (Er 3+ ) ? 4 I 13/2 (Er 3+ ) decreased. In addition, an energy-transfer process from 4 F 7/2 (Er 3+ ) to 5 D 1 (Eu 3+ ) and a cross relaxation process of 7 H 9/2 (Er 3+ ) + 5 D 0 (Eu 3+ ) ? 4 F 7/2 (Er 3+ ) + 5 D 2 (Eu 3+ ) were proposed and verified by rate equations, which dominated the energy-transfer mechanism between Er 3+ and Eu 3+ , resulted in the spectra tuning of b-NaGdF 4 :Yb 3+ ,Er 3+ . The results suggested that the color tuning of b-NaGdF 4 :Yb 3+ ,Er 3+ ,Eu 3+ UC microcrystals would have potential applications in such fields as flat-panel displays, solid-state lasers, and photovoltaics. K E Y W O R D Scolloids, modeling/model, morphology, optical materials/properties

Spatially confined luminescence process in tip-modified heterogeneous-structured microrods for high-level anti-counterfeiting

“…This indicated that Er 3+ ( 4 S 3/2 ) + Eu 3+ ( 7 F 0 ) -Er 3+ ( 4 I 15/2 ) + Eu 3+ ( 5 D 0 ) was the major energy depletion route in Yb 3+ /Er 3+ /Eu 3+ tri-doped microrods. 25 Similarly, in the Yb 3+ /Tm 3+ / Eu 3+ tri-doped samples, the lifetime of 475 nm wavelength declined from 705 to 580 ms as compared to that of NaYF 4 :Yb/Tm@NaTbF 4 :Eu microrods. This also verified the elimination of cross-relaxation of Tm-Eu pairs in the tip-modified microrods for high efficiency dual-mode luminescence.…”