Transparency-enhancement and luminescent polyvinyl butyral composite coatings and their optical modulation mechanisms

The development of transparent and luminescent coatings composing of down-conversion nanomaterials and polymers faces great challenge of trigonometric equilibrium among transparency, luminescence intensity and stability. Although inorganic down-conversion nanomaterials possess anticipated long-term performance, they would highly reduce coating transparency to preserve luminescence. Here, we investigated the optical behavior of BaMgAl₁₀O₁₇:Eu²⁺ (BAM) nanoparticles in polyvinyl butyral (PVB) coatings with a focus on their potential for enhanced transmittance besides down-conversion. Through a combination of experiments and simulations, the effects of factors such as particle size, blending amount, and coating thickness on optical properties of organic PVB composite coatings were analyzed. Small particle sizes, such as 66 nm, led to high transmittance reaching a maximum of 91.42 %, which was 1.20 % higher than that of the pristine coating, suggesting an anti-reflection phenomenon in the visible and near-infrared light spectra. The optimal blending amount and film thickness were 3 ‰ and 1 μm, respectively. Variations in these three factors caused different fluctuations in transmittance. The particle size has the greatest impact on transmittance, surpassing the effects of blending amount and coating thickness. The effect of refractive index was also investigated. In addition, the electromagnetic field on one hand influences the electronic motion state inside the coatings, thereby changing the refractive index, and on the other hand, also increases the beneficial photon scattering for achieving the anti-reflection effect. The findings provide valuable insights into the balance of transparency and luminescence in organic composite coatings.