What is the principle of metal compounds absorbing infrared rays and what are its influencing factors?

Metal compounds, including rare earth compounds, play a crucial role in infrared absorption. As a leader in rare metal and rare earth compounds, UrbanMines Tech. Co., Ltd. serves nearly 1/8 of the world's customers for infrared absorption. To address our customers' technical inquiries on this matter, our company's research and development center has compiled this article to provide answers

1.The principle and characteristics of infrared absorption by metal compounds

The principle of infrared absorption by metal compounds is mainly based on the vibration of their molecular structure and chemical bonds. Infrared spectroscopy studies molecular structure by measuring the transition of intramolecular vibration and rotational energy levels. The vibration of chemical bonds in metal compounds will lead to infrared absorption, especially metal-organic bonds in metal-organic compounds, the vibration of many inorganic bonds, and the crystal frame vibration, which will appear in different regions of the infrared spectrum.

Performance of different metal compounds in infrared spectra :

(1).MXene material: MXene is a two-dimensional transition metal-carbon/nitrogen compound with rich components, metallic conductivity, a large specific surface area, and an active surface. It has different infrared absorption rates in the near-infrared and mid-/far-infrared bands and has been widely used in infrared camouflage, photothermal conversion, and other fields in recent years.

(2).‌Copper compounds‌ : Phosphorus-containing copper compounds perform well among infrared absorbers, effectively preventing the blackening phenomenon caused by ultraviolet rays and maintaining excellent visible light transmittance and infrared absorption properties stably for a long time‌3.

Practical application cases

(1).‌Infrared camouflage‌ : MXene materials are widely used in infrared camouflage due to their excellent infrared absorption properties. They can effectively reduce the target's infrared characteristics and improve concealment‌2.

(2).‌Photothermal conversion‌ : MXene materials have low emission characteristics in the mid/far infrared bands, which are suitable for photothermal conversion applications and can efficiently convert light energy into heat energy‌2.

(3).Window materials: Resin compositions containing infrared absorbers are used in window materials to effectively block infrared rays and improve energy efficiency 3.

These application cases demonstrate the diversity and practicality of metal compounds in infrared absorption, especially their important role in modern science and industry.

2.Which metal compounds can absorb infrared rays?

Metal compounds that can absorb infrared rays include antimony tin oxide (ATO), indium tin oxide (ITO), aluminum zinc oxide (AZO), tungsten trioxide (WO3), iron tetroxide (Fe3O4) and strontium titanate (SrTiO3).

2.1 Infrared absorption characteristics of metal compounds

‌Antimony tin oxide (ATO): It can shield near-infrared light with a wavelength greater than 1500 nm, but cannot shield ultraviolet light and infrared light with a wavelength less than 1500 nm‌.

‌Indium Tin Oxide (ITO): Similar to ATO, it has the effect of shielding near-infrared light‌.

Zinc aluminum oxide (AZO): It also has the function of shielding near-infrared light.

Tungsten trioxide (WO3): It has a localized surface plasmon resonance effect and small polaron absorption mechanism, can shield infrared radiation with a wavelength of 780-2500 nm, and is non-toxic and inexpensive.

‌Fe3O4‌: It has good infrared absorption and thermal response properties and is often used in infrared sensors and detectors‌.

‌Strontium titanate (SrTiO3): has excellent infrared absorption and optical properties, suitable for infrared sensors and detectors‌.

Erbium fluoride (ErF3) : is a rare earth compound that can absorb infrared rays. Erbium fluoride has rose-colored crystals, a melting point of 1350°C, a boiling point of 2200°C, and a density of 7.814g/cm³. It is mainly used in optical coatings, fiber doping, laser crystals, single-crystal raw materials, laser amplifiers, catalyst additives, and other fields.

2.2 Application of metal compounds in infrared absorbing materials

These metal compounds are widely used in infrared absorption materials. For example, ATO, ITO, and AZO are often used in transparent conductive, antistatic, radiation protection coatings and transparent electrodes; WO3 is widely used in various heat insulation, absorption, and reflection infrared materials due to its excellent near-infrared shielding performance and non-toxic properties. These metal compounds play an important role in the field of infrared technology due to their unique infrared absorption characteristics.

2.3 Which rare earth compounds can absorb infrared rays?

Among the rare earth elements, lanthanum hexaboride and nano-sized lanthanum boride can absorb infrared rays. Lanthanum hexaboride (LaB6) is a material widely used in radar, aerospace, electronics industry, instrumentation, medical equipment, home appliance metallurgy, environmental protection, and other fields. In particular, lanthanum hexaboride single crystal is a material for making high-power electron tubes, magnetrons, electron beams, ion beams, and accelerator cathodes.

In addition, nano-scale lanthanum boride also has the property of absorbing infrared rays. It is used in the coating on the surface of polyethylene film sheets to block infrared rays from sunlight. While absorbing infrared rays, nano-scale lanthanum boride does not absorb too much visible light. This material can prevent infrared rays from entering window glass in hot climates, and can more effectively utilize light and heat energy in cold climates.

Rare earth elements are widely used in many fields, including military, nuclear energy, high technology, and daily consumer products. For example, lanthanum is used to improve the tactical performance of alloys in weapons and equipment, gadolinium and its isotopes are used as neutron absorbers in the nuclear energy field, and cerium is used as a glass additive to absorb ultraviolet and infrared rays.

Cerium, as a glass additive, can absorb ultraviolet and infrared rays and is now widely used in automobile glass. It not only protects against ultraviolet rays but also reduces the temperature inside the car, thus saving electricity for air conditioning. Since 1997, Japanese automobile glass has been added with cerium oxide, and it was used in automobiles in 1996.

3.Properties and influencing factors of infrared absorption by metal compounds

3.1The properties and influencing factors of infrared absorption by metal compounds mainly include the following aspects:

Absorption rate range: The absorption rate of metal compounds to infrared rays varies depending on factors such as metal type, surface state, temperature, and wavelength of infrared rays. Common metals such as aluminum, copper, and iron usually have an absorption rate of infrared rays between 10% and 50% at room temperature. For example, the absorption rate of pure aluminum surface to infrared rays at room temperature is about 12%, while the absorption rate of rough copper surface may reach about 40%.

3.2Properties and influencing factors of infrared absorption by metal compounds‌ :

‌Types of metals‌: Different metals have different atomic structures and electron arrangements, resulting in their different absorption capabilities for infrared rays.

‌Surface condition‌: The roughness, oxide layer, or coating of the metal surface will affect the absorption rate‌.

‌Temperature‌: Temperature changes will change the electronic state inside the metal, thereby affecting its absorption of infrared rays‌.

‌Infrared wavelength‌: Different wavelengths of infrared rays have different absorption capabilities for metals.

‌Changes under specific conditions‌: Under certain specific conditions, the absorption rate of infrared rays by metals may change significantly. For example, when a metal surface is coated with a layer of special material, its ability to absorb infrared rays can be enhanced. In addition, changes in the electronic state of metals in high-temperature environments may also lead to an increase in the absorption rate.

‌Application fields‌: The infrared absorption properties of metal compounds have important application value in infrared technology, thermal imaging, and other fields. For example, by controlling the coating or temperature of a metal surface, its absorption of infrared rays can be adjusted, allowing applications in temperature measurement, thermal imaging, etc.

‌Experimental Methods and Research Background‌: Researchers determined the absorption rate of infrared rays by metals through experimental measurements and professional studies. These data are important for understanding the optical properties of metal compounds and developing related applications‌.

In summary, the infrared absorption properties of metal compounds are affected by many factors and may change significantly under different conditions. These properties are widely used in many fields.