The Technology of UV LEDs

Welcome to the first “Professor’s Corner” of 2026! First, I would like to thank Dr. Gary Sigel of Miltec UV for providing all the articles for this column in 2025. In those articles, he introduced us to a fascinating application of UV polymerization in lithium-ion battery production. At the beginning of 2026, it may be a good time for all of us to review those four articles to continue advancing our understanding of this important technology. ^{1, 2, 3, 4}

Introduction

Let’s begin 2026 with a discussion of the technology of ultraviolet light-emitting diodes (UV LEDs). This is a relatively new technology in the UV polymerization industry that is expanding rapidly in various applications. It represents a fundamentally different method for producing UV (and visible) irradiation from that of various lamp systems, including electrode-containing arc lamps, electrodeless lamps (also known as “induction lamps”) and very high-intensity xenon-pulsed lamp systems. A major advantage of the UV LED system is that it does not utilize any mercury (Hg). Therefore, it has a positive impact on environmental issues compared to these other lamp systems.

What is an LED?

Light-Emitting Diodes (LEDs) are solid-state electronic components consisting of two different semiconductors, one that has an excess of electrons and the other that has an excess of positive “holes” (a shortage of electrons). Figure 1 shows a schematic diagram of an LED. ⁵ When an LED is connected to an electrical circuit, the electrons in the n-type semiconductor flow to the holes in the p-type semiconductor. In the process, electrons move from a higher-energy state to a lower-energy state. As the electrons move from the n-type semiconductor to the p-type, they give off photons that have the energy corresponding to the energy gap produced by the two semiconductors. ⁶ The energy difference depends on the compositions of the semiconductors. Early LEDs had an energy gap that fell within the near-infrared (NIR) region of the spectrum. Producing LEDs that emitted visible or UV photons was somewhat more challenging, as it required creating larger energy gaps between the n- and p-type semiconductors. Consequently, the process depended on the semiconductor production materials and the techniques used to produce them.

The fundamental way that semiconductors can be assembled to provide the energy gap is to utilize the Periodic Table of the Elements. Proper blending of elements in Groups III and V of the table, for example, can create semiconductors with electron-poor p-type semiconductors from Group III with electron-rich n-type semiconductors from Group V. Thus, gallium nitride (GaN), gallium arsenide phosphide (GaAsP), aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN) and other alloys have been developed for semiconductor LED applications.

History of UV LED Development

Compared to other UV lamp systems, the history of UV LEDs is significantly more recent. However, as it progressed from the first decade of the 20^th century until today, it experienced relatively long periods when little or no progress was made, as investigators encountered significant technical issues that had to be overcome. The story begins in 1907 with Henry J. Round. ⁷ He was a personal assistant to a key inventor of radio technology, Guglielmo Marconi. Round was working with a semiconductor, a substance that can either act as an electrical conductor or an insulator. The specific material that Round was working with was carborundum or silicon carbide (SiC). ⁸ When he hooked the SiC up to an electrical circuit, he noted that it gave off a yellow light. This was the first evidence reported of “electroluminescence.”

Twenty years later, in 1927, a Russian named Oleg Losev developed what is considered to be the first LED. ⁹ He, too, used SiC. But this was not a very useful invention at the time, and thus, another 35 years passed before the first practical LED was produced in 1962. During the intervening 35 years, advances were made by various people at different companies, but for a variety of reasons, they weren’t commercially successful.

In 1961, Robert Baird and Gary Pittman of Texas Instruments patented the first near-infrared (NIR) LED. ¹⁰ Then, on August 8, 1962, they filed a patent titled “Semiconductor Radiant Diode” that described an LED with a spaced cathode contact to allow for efficient emission of infrared light. ¹¹ Soon after this, in 1962, Nick Holonyak, Jr. developed the first LED that emitted visible light, a red LED that was produced using GaAsP as the semiconductor. ¹² Fast-forward to 1972, when M. George Craford, a former student of Nick Holonyak and an engineer at Monsanto, invented a red LED that was even brighter (more intense) than the one that Holonyak had reported. ¹³ He also developed a yellow LED. In the process, Craford significantly advanced LED technology.

Progress from NIR through red and then yellow LEDs was slow. It was understood that the development of green and blue LEDs would be important because they could be combined with red LEDs to make white or any color of the visible spectrum. As the systems developed from NIR to red to yellow to green and blue, the frequency of each color band increased. Thus, different semiconductors were needed that would provide ever larger energy gaps.

Then, in 1990, Isamu Akasaki, Hiroshi Amano and Shuji Nakamura made a significant breakthrough by developing a blue LED using GaN as the semiconductor. ¹⁴ To successfully commercialize this technology, it was necessary to overcome some significant manufacturing obstacles. Nakamura, Akasaki and Amano accomplished this and developed the blue LED. The significance of these developments is reflected in the fact that they received the Nobel Prize in Physics in 2014! ¹⁵

UV LEDs

Figure 2 shows a comparison of the spectral output of a 395 nm UV LED compared with the output of a Hg-based UV lamp system. A major difference between these systems is the nearly monochromatic output of the UV-LEDs vs. the broader spectral output of the conventional UV lamp. This then requires formulators to be more selective in their choice of photoinitiators.

I had intended to take this article deeper into the specifics of UV-LEDs. However, I have discovered a series of articles in archived issues of RadTech Report that cover the material in much greater detail than I can provide to you, so I refer you to eBook #1 produced by RadTech International North America. ¹⁶

Technical Questions?

What are your technical questions about polymer science, photopolymerization or other topics concerning the chemistry and technology of UV/EB polymerization? Please submit your questions or comments via email to Dianna Brodine, vice president, Editorial for Peterson Media Group, at dianna@petersonmg.com or to me at b4christmas@gmail.com.

References

1. Sigel, Gary A., “Professor’s Corner,” UV+EB Technology, 11, No. 1, pp. 36 to 40.
2. ibid., No. 2, pp. 10 to 12.
3. , No. 3, pp. 10 to 13.
4. , No. 4, pp. 12 to 15.
5. Images, Scientific Instruments, “Photovoltaic Cells-Generating Electricity,” https://www.imagesco.com/articles/photovoltaic/photovoltaic-pg4.html, (Accessed December 13, 2025).
6. Flinders, Mesh & Smalley, Ian, “What is a semiconductor?” https://www.ibm.com/think/topics/semiconductors, (Accessed December 13, 2025).
7. Wikipedia, https://en.wikipedia.org/wiki/H._J._Round, (Accessed December 13, 2025).
8. ibid.
9. VivTech, https://www.vivtechproducts.com/index.php/blog/42-the-history-of-uv-in-leds
10. Applied Electronics and Electricals, https://www.appliedelectronics.in/faq/
11. Wikipedia, https://en.wikipedia.org/wiki/History_of_the_LED# (Accessed December 13, 2025).
12. ibid.
13. ibid.
14. Lightology, https://www.lightology.com/index.php?module=how_to&sub=shuji_nakamura_blue_led&srsltid=AfmBOorKCS27Hwey0TjKm27z7oYk_5DYZrR6Utbom_3wJA9PGnXaVi1 (Accessed December 14, 2025).
15. The Royal Swedish Academy of Sciences, https://www.nobelprize.org/uploads/2018/06/popular-physicsprize2014-1.pdf (Accessed December 14, 2025).
16. https://www.radtech.org/uvledbook/RadTech_eBook1_UVLED.pdf

Byron K. Christmas, Ph.D.
Professor of Chemistry, Emeritus
University of Houston-Downtown
b4christmas@gmail.com