Browsing by Author "Dai, Pengpeng"

Now showing 1 - 2 of 2

Composition-driven anionic disorder-order transformations triggered single-Eu2+ -converted high-color-rendering white-light phosphors
(2020-01-15)
Dai, Pengpeng
;
Wang, Qingling
;
Xiang, Mei
;
Chen, Teng-Ming
;
Zhang, Xintong
Single-component, single-activator-converted high-color-rendering index (CRI) white-light phosphors have sparked much interest for phosphor-converted white light-emitting diodes. However, manipulating the distribution and locations of single activators to target desired sites in a given host lattice is still a challenge. Herein, we report the remote regulation of the distribution of Eu2+ ions by engineering and controlling the structural ordering in Sr-3(Ce1-xLax)(PO4)(3):0.05Eu(2+) (SCLP:Eu2+) compound, which are designed by using two-color phosphors with different anionic structural ordering, viz., Sr3Ce(PO4)(3):Eu2+ (yellow) with disordered state of PO4 tetrahedra, and Sr3La(PO4)(3):Eu2+ (blue) with ordered state of PO4 tetrahedra. The successive substitution of Ce by La triggers a pronounced disorder-to-order structural transformation of PO4 tetrahedra within SCLP:Eu2+ compounds and guides remotely the distribution of Eu2+ activators, which is demonstrated by a detailed analysis of synchrotron X-ray diffraction refinement, electron paramagnetic resonance spectra, electron spin-echo envelope modulation spectra, Raman spectra, nuclear magnetic resonance spectra and micro-cathodoluminescence spectrum. Benefitting from the controllable structural ordering transformation, as-prepared samples form a unique disorder-order crystal structure, exhibiting controllable microstructure acting on Eu2+ ions, tunable-color emissions including a high CRI (Ra = 90) white-light, increased structural rigidity and thermal stability. These interesting findings in the local structure-dependent luminescence properties demonstrate that structural ordering engineering may be an effective approach to regulate the migration of Eu2+ activators and improve the thermal stability of phosphors.
Sr3Ce(PO4)(3):Eu2+: a broadband yellow-emitting phosphor for near ultraviolet-pumped white light-emitting devices
(2016)
Dai, Pengpeng
;
Lee, Szu-Ping
;
Chan, Ting-Shan
;
Huang, Chien-Hao
;
Chiang, Yun-Wei
We have synthesized and investigated a series of yellow-emitting Sr3Ce(PO4)(3):Eu2+ phosphors, showing an extreme broadband at around 535 nm (with a FWHM of ca. 200 nm/6760 cm(-1)) and a large Stoke shift (ca. 8265 cm(-1)), which is attributed to the 4f-5d transition of Eu2+ without the contribution from Ce3+ emission under excitation at long wavelengths (> 370 nm). However, such broadband Eu2+ emission is rather surprising, considering that there is only one cation site for the Eu2+ luminescent center. Herein, we investigated the crystal structure by performing X-ray Rietveld refinement on the synchrotron X-ray diffraction data, and demonstrate that both cation and anion sites in Sr3Ce(PO4)(3) are disordered in the host lattice. These unusual structural characters generate a variety of distinct Eu2+ sites, which is verified by decay lifetime analysis and electron paramagnetic resonance spectra, and thus result in astonishing broadband yellow-emission. Moreover, a white LED device with a color-rendering index of 86.5, a color temperature of 5996 K, and chromaticity coordinates of (0.32, 0.38) was obtained by combining a 405 nm near-UV LED chip and the phosphor blends of yellow-emitting Sr3Ce(PO4)(3):Eu2+ and the commercial blue-emitting BaMgA(10)O(17):Eu2+ phosphor. These results indicate that the as-prepared yellow-emitting Sr3Ce(PO4)(3):Eu2+ phosphor has potential applications in the dual-color-phosphor-converted WLEDs.