On the role of secondary electrons in the color change of high-dose X-ray irradiated topaz

Owing to its high brightness, synchrotron light enables precise investigation of the physical properties of matter. High-dose X-ray irradiation can also modify materials, allowing for controlled processing. In this study, we examine the color change in natural topaz induced by synchrotron X-rays, highlighting the role of secondary electrons in forming color centers. While color enhancement of topaz is common, the underlying mechanisms remain incompletely understood. Traditionally, artificial blue coloration in topaz is achieved through high-energy particle irradiation and thermal annealing. Here, we demonstrate that permanent (i.e., remaining unchanged during storage in ambient conditions) blue coloration can be obtained using only X-rays, provided a sufficiently high dose is absorbed. This challenges the assumption that high-energies are necessary and underscores the impact of electronic mechanisms. Our findings open the door to novel, lower-energy protocols for gemstone treatment, offering a safer and potentially more accessible method for producing blue topaz for gemological applications. • High-dose X-rays induce permanent azure color in topaz, ideal for jewelry applications. • Secondary electrons drive the creation of stable O- centers and Frenkel defects. • UV-VIS and mid-IR spectra reveal mechanisms behind irradiation-induced color changes. • Thermal annealing enhances color stability by quenching metastable electronic states. • First study using high-flux synchrotron X-rays for irreversible topaz color modification.

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