High Near-infrared Reflectance Research Articles

Study on the thermal insulation property of lanthanum–cerium oxide coatings

Functional fillers with low thermal conductivity and high near-infrared reflectance play a vital role in high temperature thermal insulation coatings and make an outstanding contribution to achieving efficient comprehensive thermal insulation. In this work, the thermal insulation and bonding properties of lanthanum–cerium oxide (LCO) coatings were regulated by composition design. The effects of the La/Ce mole ratio on phase composition, the thermal conductivity and near-infrared reflectivity of LCO coatings were investigated systematically. The results showed that coating with a La/Ce mole ratio of 1:1 possess the excellent thermal insulation properties (ΔT ≈ 115°C) due to the formation of a LCO solid solution and a lanthanum phosphate mesophase with low thermal conductivity and high near-infrared reflectivity. In addition, the mortise and tenon structure was formed between the coating and the substrate, which led to the remarkable bonding properties. The LCO coating offers excellent thermal insulation properties and broad application prospects in the fields of high temperature and energy conservation.

Rapid and efficient synthesis of energy-saving cool pigments and environmental restoration materials using rare earth secondary resources

This paper proposes a method for the short-process recovery and reuse of rare earth secondary resources. Low-value rare earth polishing powder waste (WP), trichromatic phosphor waste (WT), NdFeB permanent magnetic waste (WN), and SmCo permanent magnetic waste (WS) were used as the raw materials. Based on the concept of combinatorial chemistry, energy-efficient cool pigments and environmental remediation materials were synthesized by a solid-phase method. The results showed that the synthesized materials had fluorite-type and garnet-type structures. In terms of cool pigments, doping with different rare earth permanent magnets can enrich the color (including yellow, green, brown, gray, and blue) and cause fluctuations in the near-infrared (NIR) reflectance (59.05–99.54 %) and NIR solar reflectance (55.32–95.64 %). Yellow fluorite-type pigments (WP: WT = 1:1) have the highest NIR reflectance (R = 99.54 %), while brown fluorite-type pigments (WP: WN = 1:0.1) and blue garnet-type pigments (WP:WS = 1:0.1) have relatively high NIR reflectance, 88.18 % and 59.30 %, respectively. The synthesized pigments possessed better chemical stabilities and thermal insulation performance. In terms of environmental remediation materials, the adsorption capacities of fluorite-type materials for F− and PO43− can reach 84.03 mg/g and 85.3 mg/g, respectively. In summary, materials synthesized from rare earth waste exhibit excellent potential for use in energy-efficient wastewater treatment and promote the sustainable utilization of secondary rare earth resources.

Near-infrared reflective Mg0.5Co0.5-xMnxAl2O4 black pigment synthesized by spray pyrolysis: Optimization of composition and calcination temperature

Co/Mn co-substituted MgAl2O4 pigments were spray pyrolysis, and their crystal structure and optical properties were characterized with changing the Co/Mn ratio and synthesis temperature. Regardless of the Co/Mn ratio, the resulting pigments showed spinel structured MgAl2O4 phase without any impurity phase. The synthesized Mg0.5Co0.5Al2O4 and Mg0.5Mn0.5Al2O4 showed a dark blue and brown color due to the visible light absorption by the 4A2(F) → 4T1(P) transition of Co2+ and the d-d transition of Mn2+, respectively. The black colored pigment was achieved by simultaneous substituting Co2+ and Mn2+ in the Mg2+ tetrahedral site in MgAl2O4. The optical band gap of the Mg0.5Co0.5-xMnxAl2O4 pigment decreased linearly from 3.08 eV (x = 0) to 2.46 eV (x = 0.4) as the Mn2+ content increased. As a result, Mg0.5Co0.1Mn0.4Al2O4 uniformly absorbed the entire visible light and had a black color (L* = 28.10, C* = 1.68). In terms of obtaining high near-infrared reflectance and good blackness, the optimal calcination temperature of Mg0.5Co0.1Mn0.4Al2O4 was determined to be 900 °C. The optimized Mg0.5Co0.1Mn0.4Al2O4 black pigment had a good LiDAR reflectance (38% at 905 nm) and excellent chemical stability, and showed improved heat shielding performance compared to carbon black using in black vehicles.

A new green thermal insulating ceramic pigment with high near-infrared reflectance: Mn2+ doped BaAl2O4

In this paper, a series of Ba1-xMnxAl2O4 (x = 0.00 0.02 0.05 0.10 0.15 0.20) green high NIR reflective pigments were prepared by solution gel method and applied to ceramic glaze for thermal insulation evaluation. The experimental results show that Mn2+ ions successfully replace Ba2+ ions without changing the morphology of the phase structure of the materials. The Ba1-xMnxAl2O4 morphology shows nanowire-like shape as detected by SEM. The absorption of Mn2+ ions in the visible region changes the color of the materials from white to green, and with the a* values in the range of −20.28 to −58.17, the materials have excellent coloring properties. The near-infrared reflectivity of the material in the range of 700–2500 nm is 47.35%–68.07%, which is significantly higher than other materials of the same color. In the heat insulation application experiment, the inner surface temperature of ceramic glazes with Ba1-xMnxAl2O4 materials was reduced by 16.17%–23.87% compared to ordinary ceramic samples.

Synthesis and characterization of a pigment with a high near-infrared reflectance: Ca2+-doped Bi2O3

Bi2-xCa3x/2O3 (x = 0.02, 0.04, 0.06, and 0.08) pigments with varying Ca doping levels were made via solid-phase reaction at 700 °C. The outcomes showed that the b* value could be raised from 17.13 to 41.42 by doping with a very modest quantity of Ca (x = 0.02). The pigments that were made have good NIR solar reflectance (84.6%–92.1 %) and a wide band gap (2.56–2.75eV), with the NIR reflectance peaking at x = 0.06. The pigments don't include pricey rare earth elements and are non-toxic. The colored aluminum flakes have an NIR solar reflectance of more than 50 %, which is greater than the typical (30 %) for pigments used as cooling coatings. In order to evaluate the thermal insulation performance of the coating, it was simulated as a roofing material. The findings demonstrate that under identical irradiation conditions, the coating with sample coloration exhibited a decrease in temperature of 2.3 °C in comparison to the coating with commercially available pigmentation, thermal imaging experiments show that the surface temperature of the sample coating is 3.8 °C lower than that of the commercially available coating, indicating that the sample has good heat reflection performance. Additionally, the pigment's firing temperature is low (700 °C), and it has strong chemical stability (ΔE*ab<5).

Mechanochemical preparation of low cost kaolinite-based BiVO4 hybrid pigments with high near infrared reflectance

For accelerate construction of the energy and resource-saving and environmental-friendly society, cleaner preparation of low-cost and high-performance colorful near-infrared reflective inorganic pigments with the decorative function is indispensable to reduce the hazards of urban heat island and simultaneously beautify the appearance of the buildings. Due to the non-toxicity, good chemical stability and narrow band gap, BiVO4 has been becoming a promising environment-friendly yellow inorganic pigments among the conventional heavy metals-containing inorganic pigments. In this study, the low-cost and brilliant kaolinite-based BiVO4 hybrid pigments were fabricated by cleaner mechanochemical method based on cheap and abundant kaolinite using crystal water of the hydrated metal salts as trace solvent, which could effectively promote the interaction of the involved components at the molecular level during grinding and then decreased the mass transfer resistance for the formation of monoclinic scheelite BiVO4 in the following calcination. The obtained hybrid pigments at the optimal preparation conditions exhibited brilliant color properties (D65-10°, L * = 83.45 ± 0.08, a * = 4.17 ± 0.08, b * = 88.59 ± 0.17), high near-infrared reflectance of 86.22%, infrared solar reflectance of 88.14% and high emissivity of 0.9369 in the waveband of 8–13 μm. Furthermore, the hybrid pigments could be used for coloring epoxy resin with high emissivity of 0.8782 in 8–13 μm. Therefore, the brilliant and low-cost kaolinite-based bismuth yellow hybrid pigments have the enormous potential to be served as colorful functional nanofillers for cooling roofing materials.

Cost-effective pearlescent pigments with high near-infrared reflectance and outstanding energy-saving ability for mitigating urban heat island effect

Cooling down the surface temperature of buildings and saving energy consumption are tasks of top priority in mitigating the urban heat island (UHI) effect. The bright and colorful pearlescent pigmented cool coatings with high near-infrared (NIR) reflectance possess promise in enhancing the reflective effect of solar light and the visual aspect, which is still an undeveloped domain. Herein, these novel solar reflective coatings containing mediums and pearlescent pigments with high NIR reflectance of 85% embodied obvious energy-saving effects on building materials. EnergyPlus software was used to simulate the energy-saving effect of four applied climate zones, including New York, Nanchang, Lima, and Brasilia. Compared to commercial pigments (Fe2O3, γ-Ce2S3) with similar colors, the RK 402 and RK 301 pearlescent pigments demonstrate superior energy-saving capabilities in Nanchang climate zone, and can save 1.00 kW h m−2 and 1.60 kW h m−2 annually, respectively. In the warmer climate zone of Brasilia, the highest energy-saving efficiency is 2.06 kW h m−2 over one year by RK 301 pearlescent pigment. After irradiated by an NIR lamp, the surface temperature of the RK 301 coating can be reduced by 34.8 °C compared with that of the Fe2O3 commercial coating, and that of RK 402 coating is 5.2 °C compared with the γ-Ce2S3 commercial coating. Furthermore, the 7-day field test also has consistent effect of cooling down the surface temperature. This work demonstrated that pearlescent coatings with brilliant colors have great potential for application as cold materials in building areas to mitigate the UHI effect.

Novel composite materials with high near-infrared reflectance properties to retard the thermal aging of polyethylene: Pr3+ and Er3+ doped La2Zr2O7 compounds

In this paper, Er3+ and Pr3+ successfully replaced La3+ in the lattice without changing the structure of La2Zr2O7 pyrochlore, and finally formed the substituted solid solution La2-xMxZr2O7+δ (M = Er, Pr; x = 0–0.25). SEM analysis shows that the pigments were in the shape of nearly spherical particles with a particle size between 10 and 60 nm. La2-xPrxZr2O7+δ and La2-xErxZr2O7 materials have high NIR reflectance properties, with the NIR reflectance of 68.46%–92.51% and 82.79%–90.89%, which are related to the variation of free carrier concentration due to doping content. Compared with pure polyethylene material, the polyethylene plastic samples containing La2-xPrxZr2O7+δ and La2-xErxZr2O7+δ not only had lower internal surface temperatures, 5.9–11.4 °C and 6.9–13.2 °C lower but also had significantly lower thermal aging. In conclusion, the use of synthetic pigments with high NIR reflectivity as additives can delay the thermal aging of plastics and increase the aging resilience of plastic.

+Development of a modified route for the preparation of BiVO4/ZrO2 composite with tuned heterojunction in it for efficient near-infrared solar reflectance

Recent advancements in pigmentation technology have focused on the development of cost-effective routes to achieve high near-infrared (NIR) reflectivity, offering multifunctional and sustainable applications over conventional methods. Here, we have developed a modified route for the preparation of BiVO4/ZrO2 composite with tuned heterojunction in it. Several advanced techniques were employed to investigate the elemental composition, microstructure, band gap energy, particle size, electronic transition, and color characteristics of the composite. The band gap of BiVO4 was tuned to optimize its suitability for the efficient NIR solar reflections. N2 adsorption and desorption studies indicated that the composite had a typical microporous material behavior, categorized as a type IV isotherm. Thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) revealed excellent thermal stability of the composite up to 800 °C. The equimolar ratio of the composite (1:1 BiVO4/ZrO2) composite demonstrated appreciable NIR solar reflectance, reaching 96%, and exhibited an intense yellow color with excellent color characteristics. Consequently, (1:1 BiVO4/ZrO2) composite holds significant promise as a material for the development of multifunctional, thermally stable, anti-corrosive, and energy-saving exterior cool roof applications.

Study on the effect of M/P ratio of magnesium phosphate cement coatings on reducing urban heat absorption

Using reflective coatings to enhance the reflective ability of urban underlying surface can effectively reduce building energy consumption and alleviate urban heat island effect. Magnesium phosphate cement (MPC), which consists of high near-infrared reflectivity magnesium oxide (MgO) and phosphate as the main raw materials, is a potential reflective coating. This paper studied the reflection characteristics and mechanisms of MPC with different mass ratios of MgO to phosphate (M/P). The reflectivity test results indicated that the reflectivity of MPC increased with the increase of M/P ratio, with a near-infrared reflectance of 71.74% at an M/P of 10. This was mainly related to its surface chromaticity and micromorphology. In the matter of color characteristic, it was found that the increase of M/P ratio improved the brightness and weakened the performance of other colors, which was conducive to improving the reflective effect. In the matter of micromorphology, scanning electron microscopy and energy dispersive spectrometer (SEM-EDS) analysis confirmed that there were more unreacted MgO particles and less hydration products on the MPC surface with high M/P ratio, which resulted in higher reflectivity and lower bonding strength. Finally, indoor irradiation experiments were conducted to verify the heat reduction effect of MPC coating on asphalt pavement. The results indicated that the surface temperature of the specimen coated with MPC decreased by 15.3 ℃ compared to the control specimen. Therefore, it could be concluded that MPC is a promising reflective coating that can be used to reduce urban heat absorption.

Flexible TiO2/SiO2 nanofibrous membrane with high near-infrared reflectance for thermal insulation

In this study, we successfully fabricated TiO2/SiO2 ceramic nanofibrous membranes with different molar ratios using a combination of electrospinning and sol-gel technology. The resulting nanofibers were composed of amorphous SiO2 and fine-grained anatase; the amorphous SiO2 served as a lubricating zone and refined the rutile grains in the nanofiber structure. The hybrid nanofibrous membranes exhibited exceptional mechanical properties: the highest average tensile strength was 3.22 ± 0.98 MPa, which is threefold higher than that of the TiO2 nanofibrous membranes. Consequently, the TiO2/SiO2 nanofibrous membranes withstood stretching, bending, folding, and compressing processes without breaking. Furthermore, the average reflectance of the TiO2/SiO2 nanofibrous membranes exceeded 89.57% in the range of 500–2500 nm, and their thermal conductivity at room temperature was below 0.0310 W·m − 1K−1. The flexible and robust ceramic materials have significant potential for various applications such as thermal insulation, flexible energy, and wearable electronics.

Preparation of cool composite pigment by the layer-by-layer assembling of phthalocyanine green on the surface of rutile TiO2

Purpose This study aims to fabricate a cool phthalocyanine green/TiO2 composite pigment (PGT) with high near-infrared (NIR) reflectance, good color performance and good heat-shielding performance under sunlight and infrared irradiation. Design/methodology/approach With the help of anionic and cationic polyelectrolytes, the PGT composite pigment was prepared using a layer-by-layer assembly method under wet ball milling. Based on the light reflectance properties and color performance tested by ultraviolet-visible-NIR spectrophotometer and colorimeter, the preparation conditions were optimized and the properties of PGT pigment with different assembly layers (PGT-1, PGT-3, PGT-5 and PGT-7) were compared. In addition, their heat-shielding performance was evaluated and compared by temperature rise value for their coating under sunlight and infrared irradiation. Findings The PGT pigment had a core/shell structure, and the PG thickness increased with the self-assembly layers, which made the PGT-3 and PGT-7 pigment show higher color purity and saturation than PGT-1 pigment. In addition, the PGT-3 and PGT-7 pigment showed 11%–16% lower light reflectance in the visible region. However, their light reflectance in the NIR region was similar. Under infrared irradiation the PGT-5 and PGT-7 pigment coating showed 1.1°C–3.4°C and 1.3°C–4.7°C lower temperature rise value than PGT-1 pigment coating and physical mixture pigment coating, respectively. And under sunlight the PGT-3 pigment coating showed 1.5–2.6°C lower temperature rise value than the physical mixture pigment coating. Originality/value The layer-by-layer assembling makes the core/shell PGT composite pigment possess low visible light reflectance, high NIR reflectance and good heat-shielding performance.

Low thermal conductivity and thermal radiation of La2Zr2O7 ceramics with hierarchical structure above 1000 K

The hierarchically porous La2Zr2O7 (LZO) microsphere fabricated by the electro-spraying assisted phase inversion (ESP) method is a promising feedstock for thermal barrier coatings (TBCs), due to its low thermal conductivity, quite high near-infrared reflectivity and high temperature structure stability. However, the thermal properties of hierarchically porous LZO ceramics above 1000 K are still unclear, limiting its application in TBCs. The effect of hierarchical structure on thermal conduction and thermal radiation was investigated in comparison with mono-sized pores, using the ESP microspheres (LZO-ESP) and other two carbon fillers to modulate the pores. The results showed that LZO-ESP samples exhibited ultra-low thermal conductivity (1.28 W m−1 K−1 at 1173 K), which was 30% lower than that of the reference samples of similar porosity. Heat flux simulation revealed that hierarchical structure can induce more disorder domains than the randomly distributed mono-sized pores. The disorder domains with high tortuosity of heat flux played a predominant role in the reduction of thermal conductivity. Additionally, the hierarchical structure significantly reduced thermal radiation by 36% compared with dense sample due to the decrease in transmissivity.

Cr and Mg co-doped YAlO3 red cool pigments with high NIR reflectance and infrared emissivity for sustainable energy-saving applications

Inorganic cool pigments with colors having high near-infrared (NIR) reflectance and infrared emission exhibit excellent application potential in reducing the energy consumption of buildings. In this work, a series of Cr and Mg co-doped YAlO3 red pigments were obtained by the co-precipitation method. The color properties and solar reflectance of the red pigments were regulated by tuning the amounts of Cr and Mg. The incorporation of Mg2+ can promote the generation of high-valent Cr ions and restrain absorption tail caused by oxygen vacancy. The pigment 3Cr–2Mg showed a good redness with L* = 54.55, a* = 34.05, and b* = 26.16, along with a high NIR reflectance of 71.5%. The NIR reflectance was further enhanced to 89.9% by tuning the contents of Cr and Mg. In outdoor experiments, the 1Cr-0.5Mg coating maintained a temperature that was 10.5 °C and 7.9 °C lower than the blank cement coating and the commercial Fe2O3 coating temperatures, respectively, at noon solar radiation of up to 998 Wm-2. All pigments had high infrared emissivity (8–14 μm). A temperature of 2.1 oC lower than the ambient temperature could be obtained with the coatings at night.

Deconstructed beetles: Bilayered composite materials produce green coloration with remarkably high near-infrared reflectance

Beetle elytra (hardened forewings) are a promising source of inspiration to develop or enhance the performance of human-fabricated composite materials. The structures responsible for optical properties in the ultra-violet to visible spectrum (300–700 nm) have been extensively characterised, but we have limited knowledge of optical properties and their physical origin in the near-infrared (NIR; 700–1700 nm). We examined the elytra of three species of green scarab beetles (Xylonichus eucalypti, Anoplognathus prasinus and Paraschizognathus olivaceus) with very high NIR reflectance. We manually separated layers in the elytra to disambiguate their contributions to the overall optical response. We show that unlike other scarabs, nanostructures within the cuticle layer do not produce notable reflectance. Instead, the cuticle resembles a pigment-based filter with 50% transmittance in the NIR and absorption in the visible spectrum contributing to the green appearance. Each species has a layer below the cuticle that appears white to the naked eye and produces broadband reflectance, particularly in the near-infrared; however, the structure of the white underlay differs markedly between the three species. In A. prasinus and P. olivaceus, the structure is disordered (no regular, repeated elements at optical length scales); whereas in Xylonichus eucalypti, the white underlay was notably thinner and comprised quasi-ordered hollow cylindrical structures embedded in a chitin matrix. We modelled the coherent scattering produced by this structure to demonstrate that it is responsible for broadband visible and NIR reflectance. We discuss biological implications and technological applications of the composite structure of beetle elytra.

Synthesis and characterization of Fe3+ doped YIn1-yMnyO3 black pigment with high near-infrared reflectance

Near infrared reflective inorganic pigment YIn1-x-yMnyFexO3 (x/y = 0.1–0.5) was prepared by solid state reaction. The X-ray diffraction analysis and CIE1976 L*a*b* colorimetric analysis reveal that the main phase of the sample is changed from YInO3 phase to YFeO3 phase and the color of the sample is changed from blue to black (x ≥ 0.4) with the increase of iron content. The brightness value of black pigment ranges from 23.27 to 32.12. When In3+ is replaced by Fe3+ and Mn3+, the band gap of the black sample is decreased from 1.73eV to 1.39eV. The near-infrared reflectance (R) and near-infrared solar reflectance (R*) of the sample reach the maximum when x = 0.4 and y = 0.1, which are 77.82% and 53.44%, respectively. YIn1-x-yMnyFexO3 (x = 0.4–0.5, y = 0.1–0.5) black samples have higher near infrared reflectivity than common commercial black pigments. In the thermal insulation study, under the condition of infrared irradiation for 90 min, the internal air temperature difference between the iron car model coated with YIn0.5Mn0.1Fe0.4O3 pigment and the iron car model coated with commercial iron black pigment can reach 7 °C. YIn0.5Mn0.1Fe0.4O3 black pigment was soaked in 5% acid-alkali solution for 24 h, the chromaticity was almost unchanged before and after immersion, indicating that the sample has good chemical stability. The above properties show the potential of synthetic black pigments in the field of energy conservation.

Slightly doped hydroxyapatite pigments of subtractive color with high near-infrared reflectance

A novel series of high near-infrared (NIR) reflective Ca5(PO4)3OH based pigments were synthesized by a solid-phase method. Slight single doping of Fe, Mn, and Cu can change white hydroxyapatite into yellow-orange, cyan, and red-violet, respectively. In the apatite-type structure, Fe ions would occupy the site of the Ca2+, Mn ions preferred to form MnO43− in place of PO43−, and Cu ions tended to stay in the hexagonal channel substituting the protons of OH−. When two of the elements were introduced into hydroxyapatite, the color of the co-doped materials followed the principle of subtractive color mixture. Because of the extremely low concentration of dopant, the structure of hydroxyapatite was kept undisturbed, and its high NIR reflectance was also maintained. This paper discussed chromatic properties, spectral analysis, crystalline structure, and morphology of both single-doped and co-doped samples. The economics, environment-friendly, and colorful Ca5(PO4)3OH based material is a potential cool pigment.

Light-trapping carbon nanotube forests in glass fibre-reinforced thermoplastic prepregs for efficient laser-assisted automated fibre placement

Laser-assisted automated fibre placement (LATP) is an emerging technology for manufacturing thermoplastic composite components. However, major challenges are still encountered for the LAFP process for glass fibre (GF) reinforced composites due to the high near-infrared (NIR) laser reflectance and transmission as well as resulting poor absorption of prepreg constituents. Inspired by the efficient light-trapping and photothermal characteristics of carbon nanotube (CNT) forest, we fabricate CNT forest onto the GF surface by rapid and low‐cost flame synthesis method, to enhance the photothermal conversion efficiency of poly-ether-ether-ketone (PEEK)/GF prepregs during LAFP process. CNT forests with different lengths, alignments and densities were produced by changing flame synthesis parameters. The spectroscopy results show that CNT forest suppresses transmission and reflection from GF and crystals in GF/PEEK prepreg within the NIR wavelength range at near normal incidence, decreasing transmission and reflectance to 0.3% and 7.9%, respectively, and increasing absorption to 91.8% at 1080 nm wavelength. Furthermore, CNTs forest improves the heating rate of GF/PEEK prepreg by more than 700% for a wide range of incident angles. Consequently, CNT forest enables a 400% increase in placement speed and a 79% reduction in energy consumption during LAFP process, while making negligible voids in the interlayer.

Synthesis of Blue Gahnite (ZnAl2O4:Co, Nd): A Cost-Effective Method for Producing Solar-Reflective Pigments for Cool Coatings

Developing strategies for the green synthesis of novel materials, such as pigments for protection from solar radiation, is a fundamental research subject in material science to mitigate the heat island effect. Within this perspective, the current study reports on the synthesis of blue pigments of ZnAl2O4:M (M = Co2+ and Co2+/Nd3+) using recycled metallic aluminum (discarded can seal) with reflective properties of Near-infrared radiation. The pigments were characterized by XRD, SEM, XPS, UV-Vis, NIR diffuse reflectance spectroscopy, and CIE-1976 L*a*b* color measurements. The wettability of the coatings containing the synthesized pigments was also evaluated. The structural characterization showed that the pigments present the Gahnite crystalline phase. Colorimetric measurements obtained by the CIEL*a*b* method show values correlated to blue pigments attributed to Co2+ ions in tetrahedral sites. The pigments exhibit high near-infrared solar reflectance (with R% ≥ 60%), with an enhancement of nearly 20% for the pigment-containing neodymium when applied in white paint, indicating that the prepared compounds have the potential to be energy-saving color pigments for coatings.

Disentangling thermal from alternative drivers of reflectance in jewel beetles: A macroecological study

AbstractAimTo predict future colour–climate relationships, it is important to distinguish thermal drivers of reflectance from other evolutionary drivers. We aimed to achieve this by comparing relationships between climate and coloration in ultraviolet–visible (UV–Vis) and near‐infrared (NIR) light, separately.LocationSamples were distributed primarily across Australia and North America, with some from Africa and Asia.Major taxa studiedColeoptera: Buprestidae.MethodsWe used jewel beetles as models to identify climatic drivers of reflectance, because jewel beetles have highly diverse coloration and a wide distribution and are often active in hot conditions. Specifically, we tested the association between climate, body size and reflectance using a phylogenetic comparative analysis for three wavebands (UV–Vis, NIR and total).ResultsReflectance of jewel beetles was more strongly predicted by body size than by climate. NIR reflectance and total reflectance were not associated with climate, but larger beetles had higher NIR reflectance. For UV–Vis reflectance, small beetles were darker in warmer and more humid environments, whereas there was no association with climate for large beetles.Main conclusionsOur study suggests that variation in reflectance of jewel beetles is not driven by thermal requirements and highlights the importance of considering NIR reflectance when evaluating explanations of the effects of colour on thermoregulation.