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Dual-Spectral Design of Porous Anodic Alumina for Tunable Colored Passive Radiative Cooling
Zeinelabedin A Mohamed1,2, Maksymilian Włodarski3, Małgorzata Norek1
1Institute of Materials Science and Engineering, Faculty of Advanced Technologies and Chemistry, Military University of Technology, Warsaw, Poland.
Small (Weinheim an Der Bergstrasse, Germany)
|July 15, 2026
Summary
Researchers developed a new porous anodic alumina (PAA) material for passive radiative cooling. This material achieves tunable structural colors and high mid-infrared emissivity, crucial for efficient cooling applications.
Area of Science:
- Materials Science
- Nanotechnology
- Optics
Background:
- Passive radiative cooling demands materials with high mid-infrared (MIR) emissivity (8-13 µm) and low solar absorption.
- Porous anodic alumina (PAA) offers tunable nanostructures and intrinsic infrared emission but struggles with independent spectral control.
- Integrating visible photonic properties with MIR emissivity in a single PAA architecture is a significant challenge.
Purpose of the Study:
- To demonstrate dual-spectral control in PAA photonic structures for radiative cooling.
- To achieve tunable structural coloration while maintaining high MIR emissivity.
- To explore the relationship between visible photonic properties and MIR emissivity in PAA.
Main Methods:
- Utilized charge density-controlled sinusoidal pulse anodization of PAA integrated with aluminum (Al) substrates.
- Employed periodic voltage modulation to create photonic stop bands (PSBs) in the visible spectrum.
- Systematically varied pore widening to analyze shifts in PSBs and reflectance.
Main Results:
- Successfully generated tunable structural colors via visible-range PSBs using voltage modulation.
- Preserved high MIR emissivity independently of visible spectral modifications.
- Observed a progressive blue shift in PSBs with pore widening, indicating distinct control mechanisms.
- PAA architecture facilitated optical impedance matching, and the Al substrate minimized transmission losses.
Conclusions:
- PAA is a versatile platform for designing radiative cooling surfaces with independent optical and thermal functionalities.
- Dual-spectral control of visible and MIR properties is achievable in PAA structures.
- The developed method enables color-designed radiative cooling with engineered optical properties.
