Near-Infrared Luminescent Materials: From Archaeological Significance to Biomedical Applications

Near infrared (NIR) luminescent materials have emerged as a growing field of interest, particularly for biomedical imaging and optics applications¹ including but not limited to transition metal based NIR luminescent pigments. Egyptian blue (CaCuSi₄O₁₀), an inorganic pigment with Cu²⁺ as the photoactive luminescent center (emission at λ = 910 nm), has several applications such as environmental optical sensing material² and fingerprint detection³. The discovery and production of Egyptian blue can be dated back to old kingdom Egypt ca. 2600 BCE⁴. Around the same period, faience, a glazed quartz-based ceramic has also been produced in near east and Egypt. Both Egyptian blue and faience share three common elements – silicon, calcium, and copper – and similar synthetic conditions, yet no connection has been established nor reported in the literature although semiquantitative NIR analysis of ancient faience samples reveals the presence of Egyptian blue.

For biomedical imaging applications, a longer NIR wavelength window (λ = 1000 – 1500 nm) is required to achieve higher imaging sensitivity and resolution⁵. Manganese blue is a blue green synthetic pigment which has been reported in the patent literature in 1935⁶ featuring a barium sulfate host with manganese doped in the barium sulfate crystal matrix replacing some of the sulfur ions. The pigment is characterized by NIR emission profile at λ = 1300 nm making it a potential candidate for biomedical imaging applications. In addition, manganese blue has been reported to possess superior stability to acids, alkalis, heat, and light⁷.

The first part of this seminar talk discusses the in-situ synthesis and characterization of Egyptian blue in faience with emphasis on Egyptian blue – faience continuum. By altering the concentration of the calcium source and in some instances the concentration of copper we obtained either a faience on one end of the continuum and Egyptian blue on the other extreme. We took advantage of our findings, and we extended our work to growing Egyptian blue crystals in faience using techniques such as slow cooling and air quenching. The second part details different synthetic approaches and characterization techniques for manganese blue pigment. Through a melt flux synthetic approach and annealing studies, we were able to make conclusions about the oxidation state of manganese, optimal synthetic temperature, and  morphology of manganese blue crystals. Finally, the talk will explore different challenges, work in progress, and potential applications.

1. Jackson, C.T., Jeong, S., Dorlhiac, G.F. and Landry, M.P. Advances in Engineering Near Infrared Luminescent Materials. Iscience, 2021, p.102156.
2. Borisov, S.M., Würth, C., Resch-Genger, U. and Klimant, I. New life of ancient pigments: application in high-performance optical sensing materials. Analytical chemistry, 2013, 85(19), p.9371-9377.
3. Shahbazi, S., Goodpaster, J.V., Smith, G.D., Becker, T. and Lewis, S.W. Preparation, characterization, and application of a lipophilic coated exfoliated Egyptian blue for near-infrared luminescent latent fingermark detection. Forensic Chemistry, 2020, 18, p.100208.
4. Liang, H., Sax, M., Saunders, D. and Tite, M. Optical coherence tomography for the non-invasive investigation of the microstructure of ancient Egyptian faience. Journal of Archaeological Science, 2012, 39(12), p.3683-3690.
5. Zhao, J., Zhong, D. and Zhou, S. NIR-I-to-NIR-II fluorescent nanomaterials for biomedical imaging and cancer therapy. Journal of Materials Chemistry B, 2018, 6(3), pp.349-365.
6. Accorsi, G., Verri, G., Acocella, A., Zerbetto, F., Lerario, G., Gigli, G., Saunders, D. and Billinge, R. Imaging, photophysical properties and DFT calculations of manganese blue (barium manganate (vi) sulphate)–a modern pigment. Chemical Communications, 2014, 50(97), pp.15297-15300.
7. Korinth, E., et al. US Patent 2, 156, 727, 1939.