Author: Site Editor Publish Time: 25-11-2025 Origin: Site
Ultraviolet (UV) radiation is the segment of the electromagnetic spectrum between visible light (violet, wavelength ~400 nm) and X-rays (wavelength ~10 nm), with a wavelength range typically defined as 100 nm to 400 nm. From the perspective of quantum theory, the core characteristic of UV light lies in its wavelength: the shorter the wavelength, the higher the photon energy, resulting in greater destructive power on matter (especially biomolecules). This property endows UV with significant applications in disinfection, curing, and other fields, while also posing potential biological hazards (e.g., excessive exposure can damage skin or DNA).
The Sun is the primary natural source of UV radiation on Earth, generating high-energy photons through internal nuclear fusion. After filtering by the atmosphere, only portions of UVA (320–400 nm) and a small amount of UVB (280–320 nm) reach the surface. Atmospheric components like the ozone layer absorb most UV radiation, especially the highest-energy UVC (200–280 nm), thereby protecting Earth's ecosystems from its destructive effects.
Based on wavelength and energy differences, UV is divided into three categories:
UVA (320–400 nm): Long-wave UV, with strong penetration, mainly used for curing, fluorescence detection, and black lights, but it may accelerate skin aging.
UVB (280–320 nm): Medium-wave UV, with moderate energy, used in medical treatments (e.g., for skin conditions) and vitamin D synthesis, but it easily causes sunburn.
UVC (200–280 nm): Short-wave UV, with the highest energy, almost completely absorbed by the atmosphere, possessing extremely strong germicidal capabilities by destroying microbial DNA/RNA structures. It is commonly used in disinfection applications, such as air purification and water treatment.
First method: Finding an atom whose electron excitation energy difference from the ground state falls exactly in the UV range. We know that electron transitions in atomic orbitals convert energy into electromagnetic waves. Fortunately, the periodic table includes elements that meet this requirement.
Unfortunately, this element is mercury (Hg), commonly known as quicksilver, which is harmful to humans and the environment. Mercury lamps (or mercury vapor lamps) are currently the mainstream products for UV disinfection, curing, and exposure, and they are also the largest application for fluorescent tubes and compact fluorescent lamps (CFLs). The working principle of mercury lamps is relatively simple: in a cathode ray tube, high-energy electrons excite mercury vapor atoms, causing their electrons to enter an excited state; when the electrons return to the ground state, they release UV light (primarily at 253.7 nm and 185 nm wavelengths). If the outer wall of the lamp tube is coated with RGB phosphor, the UV light can be converted into visible light, forming fluorescent or energy-saving lamps. Currently, mercury lamps remain the dominant technology for UV disinfection, curing (e.g., UV ink printing), and exposure (e.g., semiconductor lithography). However, due to mercury's toxicity, international conventions like the Minamata Convention are pushing for its phased elimination.
Second method: Using semiconductor light-emitting principles to manufacture UV-band light sources.
UVC LED (Ultraviolet C Light-Emitting Diode) is an innovative modern UV light source solution. It is based on the luminescence principle of semiconductor materials, particularly III-V compound semiconductors such as aluminum nitride (AlN), gallium nitride (GaN), and indium gallium nitride (InGaN). The bandgap of these materials (approximately 2.5–6.2 eV) corresponds precisely to the blue-to-UV wavelength range, allowing precise control of the emission wavelength by adjusting the composition ratios.
This technological breakthrough originated in the early 1990s from the contributions of Japanese scientists Shuji Nakamura, Isamu Akasaki, and Hiroshi Amano, who solved the challenges of gallium nitride crystal growth. Using methods like metal-organic chemical vapor deposition (MOCVD), multilayer structures (such as AlGaN/AlInGaN heterojunctions) are grown on sapphire or silicon substrates to produce LED chips covering UVA, UVB, and even UVC bands.
Sterilization Principle of UVC LED
The germicidal effect of UVC LED stems from the destructive action of its short-wave UV light (especially in the 222–280 nm band) on microbial nucleic acids. The specific mechanisms are as follows:
Nucleic Acid Absorption and Damage: Microorganisms (such as bacteria, viruses, fungi, and protozoa) have DNA or RNA containing pyrimidine bases (thymine T or uracil U), which exhibit high absorption rates for UVC light (peak at ~260 nm). When UVC photons are absorbed, they excite adjacent pyrimidine molecules to form dimers (pyrimidine dimers), most commonly thymine dimers.
Disruption of Genetic Function: These dimers distort the DNA double-helix structure, interfering with the normal operation of DNA polymerase, leading to errors or stagnation in DNA replication and RNA transcription. As a result, microorganisms cannot synthesize proteins normally, reproduce, or maintain metabolism, ultimately becoming inactivated or dying.
Inactivation Efficiency and Dose: The germicidal effect depends on the irradiation dose (mJ/cm² = irradiance × time). For example, 99.9% inactivation of Escherichia coli requires about 6–10 mJ/cm², while for SARS-CoV-2, it requires about 3–5 mJ/cm². The advantages of UVC LED include precise control of wavelength and dose, no ozone production or chemical residues, and effectiveness against drug-resistant bacteria.
UVC LEDs have a wide range of applications, including hospitals, air conditioning systems, disinfection cabinets, water treatment equipment, water dispensers, sewage treatment plants, swimming pools, and food and beverage processing and packaging equipment. In summary, UVC LED represents a revolutionary shift in UV technology from traditional mercury lamps to sustainable solid-state light sources. It is not only safer and more efficient but also opens innovative prospects in the disinfection field. With advancements in materials science and manufacturing processes, UVC LEDs are expected to dominate the global UV market by 2030, completely replacing mercury lamps and promoting "mercury-free" and intelligent applications.
