Abstract
Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature <4000 K) with good color rendition (i.e., color rendering index >80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors’ emission spectrum. Here, we report a new yellow Ba0.93Eu0.07Al2O4 phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature <4000 K and color rendering index >80 were readily achieved when combining the Ba0.93Eu0.07Al2O4 phosphor with a blue light-emitting diode (440–470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index >80) can be achieved based on single-phosphor, single-emitting-center conversion. Scientists have developed a yellow phosphor that can be used to provide a pleasing white light with a warm color temperature when combined with a blue light-emitting diode (LED) chip. Although YAG: Ce-based white LEDs show great promise as a highly efficient and long-lasting form of domestic lighting, their cool bluish-white light makes them undesirable for use in the home. Scientists from the USA and China have now shown that a new phosphor, Ba0.93Eu0.07Al2O4, when combined with a blue InGaN LED, provides a pleasing white light with a warm colour temperature of less than 4000K and a high colour-rendering index of more than 80. The phosphor has an orthorhombic structure and was manufactured by carbothermal reduction and vapour phase deposition in a tube furnace system. This work suggests that high-quality, warm-white lighting can be achieved using a combination of a single phosphor with single-emitting-center and a blue LED chip.
Highlights
White-light sources based on light-emitting diodes (LEDs) have a promising future in general illumination with advantages over conventional lighting sources, because they are energy-saving, compact and rigid, long-lived and environmentally benign.[1,2,3] The most popular approach for producing commercial white LEDs is based on a single-phosphor, single-emitting-center-conversion model, which is made by coating an InGaN blue LED with a yellow-emitting phosphor
Despite their wide applications and high luminous efficacy (.100 lm W21), one deficiency for white LEDs using only YAG:Ce is that they are limited to high correlated color temperature (CCT; usually,6000 K) and low color rending index (CRI; usually,75), due to the lack of sufficient red spectral component.[4,6,7]
EDS composition analyses revealed that both powder and wires are composed of Ba, Al, Eu and O (Figure 1g), and each element is uniformly distributed across the particles or wires, as measured by EDS
Summary
White-light sources based on light-emitting diodes (LEDs) have a promising future in general illumination with advantages over conventional lighting sources (e.g., incandescent, fluorescent and highintensity discharge lamps), because they are energy-saving, compact and rigid, long-lived and environmentally benign.[1,2,3] The most popular approach for producing commercial white LEDs is based on a single-phosphor, single-emitting-center-conversion model, which is made by coating an InGaN blue LED with a yellow-emitting phosphor. The first as well as the most widely used yellow phosphor is Ce31-doped Y3Al5O12 (YAG:Ce), owing to its many favorable properties such as strong absorption of blue light (,420– 480 nm), broad emission band in the visible region (500–700 nm), fast luminescence decay time (,100 ns), high external quantum efficiency (QE, ,75% under blue LED excitation), remarkable chemical and thermal stability and easy synthesis.[4] By virtue of these advantages, white LEDs made of a blue LED and a YAG:Ce phosphor are currently the mainstream in the market and are being widely used in point light sources, and wide-illumination equipment, back-lighting of liquid-crystal TVs and high-power automotive headlights.[5]. Despite their wide applications and high luminous efficacy (.100 lm W21), one deficiency for white LEDs using only YAG:Ce is that they are limited to high correlated color temperature (CCT; usually ,6000 K) and low color rending index (CRI; usually ,75), due to the lack of sufficient red spectral component.[4,6,7] The resulting cool, bluish-white light makes such devices undesirable for indoor use
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