Photoluminescence properties and energy transfer in a novel Sr 8 ZnY(PO 4 ) 7 :Tb 3+ ,Eu 3+ phosphor with high thermal stability and its great potential for application in warm white light emitting diodes
Mao Xia (Central South University China, Hunan Agricultural University)
Xianbo Wu (Hunan Agricultural University)
Yuan Zhong (Hunan Agricultural University)
Hubertus T. Bert Hintzen (TU Delft - RST/Luminescence Materials)
Zhi Zhou (Hunan Agricultural University)
Jing Wang (Sun Yat-sen University, Hunan Agricultural University)
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Abstract
Terbium and europium co-doped Sr
8
ZnY(PO
4
)
7
phosphors are successfully prepared through a high temperature solid-state reaction (SSR). The crystal structure of the as-prepared samples was identified to be Sr
8
ZnY(PO
4
)
7
(SZYP) pure phase by an X-ray powder diffraction technique. Under near-ultraviolet light excitation (378 nm), the SZYP:Tb
3+
and SZYP:Eu
3+
phosphors show green and red emission peaking at 545 and 618 nm, respectively. Moreover, an effective energy transfer process from Tb
3+
to Eu
3+
could be verified by the concentration dependence of emission intensity and lifetime. The energy transfer mechanism between Tb
3+
and Eu
3+
is determined to be governed by dipole-dipole interactions. The internal quantum efficiency (IQE) is evaluated to be as high as about 91%. The temperature-dependent spectra indicate that the SZYP:Tb
3+
,Eu
3+
phosphor shows a high thermal stability. Furthermore, the as-fabricated white LED devices exhibit an excellent correlated color temperature (CCT) of 3223 K, a color rendering index (R
a
) of 85.8 and a luminance efficiency of 37.4 lm W
-1
. All results imply that the SZYP:Tb
3+
,Eu
3+
phosphors have a great potential for application in white LEDs.
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