Novel rare-earth-free yellow Ca5Zn3.92In0.08(V0.99Ta0.01O4)6 phosphors for dazzling white light-emitting diodes.

E Pavitra,G Seeta Rama Raju,Jin Young Park,Lili Wang,Jae Su Yu,Byung Kee Moon

doi:10.1038/srep10296

E Pavitra, G Seeta Rama Raju + Show 4 more

Open Access

https://doi.org/10.1038/srep10296

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Abstract

White light-emitting diode (WLED) products currently available on the market are based on the blue LED combined with yellow phosphor approach. However, these WLEDs are still insufficient for general illumination and flat panel display (FPD) applications because of their low color-rendering index (CRI < 75) and high correlated color temperature (CCT = 6000 K). Although near-ultraviolet (UV) LED chips provide more efficient excitation than blue chips, YAG:Ce3+ phosphors have very weak excitation in the near-UV spectral region. Hence, there is an increasing demand for novel yellow phosphor materials with excitation in the near-UV region. In this work, we report novel self-activated yellow Ca5Zn3.92In0.08(V0.99Ta0.01O4)6 (CZIVT) phosphors that efficiently convert near-UV excitation light into yellow luminescence. The crystal structure and lattice parameters of these CZIVT phosphors are elucidated through Rietveld refinement. Through doping with In3+ and Ta5+ ions, the emission intensity is enhanced in the red region, and the Stokes shift is controlled to obtain good color rendition. When a near-UV LED chip is coated with a combination of CZIVT and commercial blue Ba0.9Eu0.1MgAl10O17 phosphors, a pleasant WLED with a high CRI of 82.51 and a low CCT of 5231 K, which are essential for indoor illumination and FPDs, is achieved.

Highlights

White light-emitting diode (WLED) products currently available on the market are based on the blue light-emitting diodes (LEDs) combined with yellow phosphor approach
The morphological properties of the CZIVT self-activated phosphors annealed at 800 °C were examined using field-emission scanning electron microscope (FE-SEM) and transmission electron microscope (FE-TEM) images
The Rietveld refinement confirmed that these phosphors possessed a pure cubic garnet structure, and the high-resolution TEM (HRTEM) and selected area electron diffraction (SAED) patterns indicated that the particles were single crystalline

Summary

Introduction

White light-emitting diode (WLED) products currently available on the market are based on the blue LED combined with yellow phosphor approach These WLEDs are still insufficient for general illumination and flat panel display (FPD) applications because of their low color-rendering index (CRI < 75) and high correlated color temperature (CCT = 6000 K). It has been reported that some of these vanadates have unusual luminescent properties, such as broad and intense oxygen-to-metal charge transfer (CT) bands typically observed in the near-UV region, thereby allowing for the efficient capture of emissions over a large wavelength range (400–700 nm) This type of self-activated vanadate phosphor possesses many advantages over rare-earth-activated phosphors. The fabricated WLED exhibited unique properties, such as a high CRI (82.51) and a low correlated color temperature (5231 K), which are prerequisites for general illumination and flat panel display applications

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