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
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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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