Because of properties such as wide band transparency, good chemical and thermal stability, low dispersion, high laser damage enhance the optical and electrical properties of glass. Metals, oxides, non-oxides, and semiconductors can be dispersed in glass-ceramics, and these nanocrystals precipitated in glass can not only enhance the mechanical properties of the glass, but also provide properties that the glass substrate does not have.
When these nanocrystals are introduced into glass, the bright color of the glass will appear due to the localized surface plasmon resonance (LSPR) effect. This optical effect based on the particle size can be interpreted as: the free electrons of metals limited to subwavelength nanoparticles will have LSPR under certain frequency excitation. This effect will cause the electric field near the surface of the nanoparticles to increase by 3 to 6 orders of magnitude, thus greatly promoting the interaction between light and matter, and it shows the strong linear absorption in the resonance band. Its absorption cross-section is at least 2 orders of magnitude larger than that of quantum dots, organic dyes and various optically active ions.
Among the different compositions of nanocrystals, precious metal nanocrystals may be one of the earliest used by humankind. In most oxide glass systems (such as silicate glass systems), noble metals such as Au, Ag, and Pt are difficult to form stable chemical bonds with the glass network. After heat treatment, these metal elements are easy to precipitate in clusters or nanocrystals. At present, a variety of noble metal nanocrystalline doped glass systems have been widely studied. In addition, some other plasmon materials such as non-precious metals can also be precipitated from some specific compositions of glass. Except for noble metal, nanocrystals that can be precipitated from glass include oxide and non-oxide systems such as ZnO:Sb, Cu2–xSe, RuO2, etc.
At present, the most widely used methods to precipitate plasmon nanocrystals from glass are heat treatment, ion implantation and femtosecond laser induced precipitation. Heat treatment is a common method for precipitating nanocrystals into the glass. The advantage of the heat treatment method is that it’s easy to operate. The disadvantage is that even after the same heat treatment process, the precipitation state of the nanocrystals cannot be guaranteed to be completely consistent, and it is difficult to fine-tune the size, distribution and shape of the nanocrystals. The ion implantation method is to accelerate the target doped ions into a high speed ion beam by a strong electric field and drive it into the glass matrix. Then the injected ion is crystallized by heat treatment. The advantage of ion implantation is that any kind of ion can be injected into the glass theoretically. The shape, size and structure of the nanoparticles can be controlled by adjusting the implantation parameters. The disadvantage of ion implantation is that the equipment is expensive and nanocrystals can only be precipitated on the glass surface, and the size and depth distribution of nanocrystals is not well controlled. The femtosecond laser irradiation method uses femtosecond laser with short action time and high spatial freedom to control the size and spatial distribution of nanocrystals in glass. The nanoparticles can dissolve again through femtosecond laser.
It is generally believed that glass does not have the second-order nonlinear polarization effect and the third-order nonlinear response of glass is relatively weak since it’s isotropic. We can involve nanocrystals with LSPR effect into glass to enhance its nonlinear polarization performance. Due to its strong resonance absorption in the LSPR band and the nonlinear response here also appears the extreme value, the plasmon nanoparticles participated glass has a wide application prospect not only in the frontier fields such as optical grating, optical storage, sensing and detection, but also in the nonlinear fields such as ultrafast optical switching,optical modulation and pulse laser.
Summary and prospects The optical properties and preparation methods of various kinds of plasmon nanocrystalline glasses containing precious metals and non-precious metals are briefly introduced in this paper. Due to the LSPR effect of plasmon materials, glass containing plasmon nanocrystals exhibit huge resonance absorption and strong nonlinear response in the resonance band, which makes them widely used in ultrafast photonics and nonlinear optics fields. However, the strong resonance absorption of plasmon also means huge linear absorption loss, which limits its application in, for example, the nonlinear optical switching. In addition, in the glass matrix, the growth of plasmon nanocrystals is limited. It’s very difficult to control their geometric structure and composition,which makes their optical properties difficult to control. The emergence of ultrafast laser processing technology provides a new means for the spatially selective precipitation of plasmon nanocrystals, which also serves as a powerful processing tool for developing photonic devices based on this kind of glass.