To be more energy efficient, many people have replaced their incandescent lights with light-emitting diode bulbs. However, those currently on the market emit a lot of blue light, which has been linked to eye troubles and sleep dis­turbances. Now, researchers from the University of Houston have developed a proto­type LED that reduces – instead of masks – the blue component, while also making colors appear just as they do in natural sunlight.

LED light bulbs are popular because of their low energy consump­tion, long lifespan and ability to turn on and off quickly. Inside the bulb, an LED chip converts electrical current into high-energy light, including invisible ultra­violet, violet or blue wavelengths. A cap that is placed on the chip contains multiple phosphors – solid lumi­nescent compounds that convert high-energy light into lower-energy visible wave­lengths. Each phosphor emits a different color, and these colors combine to produce a broad-spectrum white light. Commercial LED bulbs use blue LEDs and yellow-emitting phosphors, which appear as a cold, bright white light similar to daylight. Continual exposure to these blue-tinted lights has been linked to cataract formation, and turning them on in the evening can disrupt the production of sleep-inducing hormones, such as melatonin, triggering insomnia and fatigue. To create a warmer white LED bulb for nighttime use, previous researchers added red-emit­ting phosphors, but this only masked the blue hue without getting rid of it. So, Jakoah Brgoch and Shruti Hariyani wanted to develop a phosphor that, when used in a violet LED device, would result in a warm white light while avoiding the pro­blematic wavelength range. 

As a proof of concept, the researchers identified and synthesized a new lumi­nescent crystal­line phosphor containing europium ((Na_1.92Eu_0.04)MgPO₄F). In thermal stability tests, the phosphor's emission color was consistent between room tempera­ture and the higher operating temperature of commer­cial LED-based lighting. In long-term moisture experi­ments, the compound showed no change in the color or intensity of light produced. To see how the material might work in a light bulb, the researchers fabricated a prototype device with a violet-light LED covered by a silicone cap containing their lumi­nescent blue compound blended with red-emitting and green-emitting phosphors.

It produced the desired bright warm white light while mini­mizing the intensity across blue wave­lengths, unlike commer­cial LED light bulbs. The prototype's optical properties revealed the color of objects almost as well as natural sunlight, ful­filling the needs of indoor lighting, the researchers say, though they add that more work needs to be done before it is ready for everyday use. (Source: ACS)

Reference: S. Hariyani & J. Brgoch: Advancing Human-Centric LED Lighting Using Na₂MgPO₄F:Eu²⁺, ACS Appl. Mater. Interfaces 13, 16669 (2021); DOI: 10.1021/acsami.1c00909

Link: Dept. of Chemistry, University of Houston, Houston, USA