Phosphor For Warm White Light-emitting Diodes Research Articles

Highly effective red phosphor for warm white LEDs without rare earth elements

The use of red fluorescent powder derived from nitrides and oxides in warm white LEDs is a pressing concern due to its lower quantum efficiency. Fluoride red phosphors activated by Mn4+ ions show promising potential for application in white light-emitting diodes (LEDs) due to their distinctive narrowband red emission and broad blue excitation, along with the relatively mild synthesis conditions required. However, the quantum efficiency of early Mn4+-doped fluoride phosphors was not optimal, highlighting the importance of identifying a suitable preparation method and matrix. Here, we introduce an efficient and thermally stable red fluoride phosphor, Cs2SiF6:Mn4+, which demonstrates a remarkable quantum efficiency of 98.32 % achieved through ion exchange techniques. However, even at a temperature of 423 K, the luminous intensity still maintained at 95 % of that under room temperature conditions. By incorporating Cs2SiF6:Mn4+ as a red emitter, a stable 10 W high-power warm white LEDs with a luminous efficiency of approximately 126.1 lm/W can be realized. These findings underscore the significant potential of the red phosphor Cs2SiF6:Mn4+ in advancing high-performance, high-power warm white LEDs.

New yellow Ba0.93Eu0.07Al2O4 phosphor for warm-white light-emitting diodes through single-emitting-center conversion

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.

Rare earth doped core-shell particles as phosphor for warm-white light-emitting diodes

Light-emitting diodes (LEDs) are efficient, energy-saving light sources. Unfortunately, designing phosphors for LEDs that emit warm white light is not straightforward. We solvothermally prepared rare earth doped alkaline earth sulfides with a core-shell structure in order to obtain a physical separation between different dopants (europium and cerium). Cathodoluminescence of a single phosphor particle in an electron microscope proves simultaneous Eu2+ and Ce3+ broad band emission. The emission color can be tuned by variation of the composition, core size, and shell thickness. Upon excitation of SrS:Eu2+-SrS:Ce3+ core-shell structures at 430 nm, white light emission with good color rendering and a color temperature around 3000 K is obtained.