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Subjects:
Materials Science, Ceramics
Glass inhomogeneities represent variations in the structural or compositional uniformity of glass, traditionally associated with process-related defects such as striae, bubbles, stones, and inclusions that impair transparency and mechanical stability. These “technological” inhomogeneities emerge during melting, forming, or annealing, and have long been the focus of industrial elimination strategies. However, recent developments in glass science and nanotechnology have reframed inhomogeneity as a potential asset. When precisely engineered at the nanoscale, inhomogeneities, such as nanocrystals, metal or semiconductor nanoparticles, and nanopores, can enhance glass with tailored optical and photonic functionalities, including upconversion luminescence, plasmonic response, nonlinear refractive behavior, and sensing capabilities. This entry provides an integrated perspective on the evolution of glass inhomogeneities, tracing the shift from defect suppression to functional nanostructuring. It discusses both the traditional classification and mitigation of detrimental defects, and the design principles enabling the intentional incorporation of beneficial nanoinhomogeneities, particularly in the context of optics and photonics. The utilization of engineered inhomogeneities in nuclear waste glasses is also discussed.
- glass inhomogeneity
- glass defects
- bubbles
- nanocrystals
- nanopores
- nanostructuring
Inhomogeneities in glass are any non-uniformities in composition or structure that lead to local variations in properties (especially refractive index) [1]. Traditionally, glassmaking strove for extreme homogeneity: any streaks, bubbles, or inclusions were considered defects to be eliminated because they scatter or distort light [2]. For example, early optical lenses often suffered from striae (“veins” or cords of slightly different refractive index) that blurred images, until the introduction of vigorous stirring in 1805 by P.L. Guinand greatly improved homogeneity. Over the 19th and 20th centuries, techniques like careful batch preparation, controlled melting, and fine annealing were developed to produce glass that was as uniform as possible, free of visible striae, “seeds” (small bubbles), or inclusions. The historical mindset was clear: such inhomogeneities were “faulty” and had to be mitigated for glass to meet technological demands in optics, containers, etc. [3].
Today, however, a new paradigm has emerged. Advances in materials science and nanotechnology have shown that not all inhomogeneity is detrimental. It is now possible to engineer nanoscale inhomogeneities intentionally to impart novel functionalities to glass. By introducing controlled nanosized second phases or structures (crystals, particles, pores, etc.) into a glass matrix, researchers create composite materials with enhanced optical or photonic properties [4]. The once-“forbidden” heterogeneity is harnessed in a positive way; for example, embedding metallic nanoparticles can produce intense plasmonic absorption and local-field enhancements, and precipitating nanocrystals can enable luminescence or nonlinear optical effects that homogeneous glass lacks [5]. Another example is the utilization of inhomogeneities in the form of crystalline phases embedded in durable glasses aiming to immobilize the radioactive and toxic nuclides of nuclear waste [6].
This article reviews this remarkable transition: from the classical “faulty” inhomogeneities (unwanted process-induced defects) to “desired” inhomogeneities (designed nanostructures that add functionality). We begin by surveying conventional glass defects—their nature, origins, and how they are detected and eliminated—and then discuss the burgeoning field of functional nanoinhomogeneous glasses for optics and photonics.
This entry is adapted from the peer-reviewed paper 10.3390/encyclopedia5030136
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