Published values of crystal growth rates are compared for supercooled glass-forming liquids undergoing congruent freezing at a planar crystal-liquid interface. For the purposes of comparison pure metals are considered to be glass-forming systems, using data from molecular-dynamics simulations. For each system, the growth rate has a maximum value U_max at a temperature T_max that lies between the glass-transition temperature T_g and the melting temperature T_m. A classification is suggested, based on the lability (specifically, the propensity for fast crystallization), of the liquid. High-lability systems show “fast” growth characterized by a high U_max, a low T_max / T_m, and a very broad peak in U vs. T / T_m. In contrast, systems showing “slow” growth have a low U_max, a high T_max / T_m, and a sharp peak in U vs. T / T_m. Despite the difference of more than 11 orders of magnitude in U_max seen in pure metals and in silica, the range of glass-forming systems surveyed fit into a common pattern in which the lability increases with lower reduced glass-transition temperature (T_g / T_m) and higher fragility of the liquid. A single parameter, a linear combination of T_g / T_m and fragility, can show a good correlation with U_max. For all the systems, growth at U_max is coupled to the atomic/molecular mobility in the liquid. It is found that, across the diversity of glass-forming systems, T_max / T_g = 1.48 ± 0.15.

We studied the optical properties of as-prepared (amorphous) and thermally crystallized (fcc) flash evaporated ${\text{Ge}}_2{\text{Sb}}_2{\text{Te}}_5$ thin films using variable angle spectroscopic ellipsometry in the photon energy range 0.54–4.13 eV. We employed Tauc–Lorentz (TL) model and Cody–Lorentz (CL) model for amorphous phase and TL model with one additional Gaussian oscillator for fcc phase data analysis. The amorphous phase has optical bandgap energy $E_g^{\text{opt}}=0.65\text{eV}$ (TL) or 0.63 eV (CL) slightly dependent on used model. The Urbach edge of amorphous thin film was found to be $\sim 70\text{meV}$ . Both models behave very similarly and accurately fit to the experimental data at energies above 1 eV. The CL model is more accurate in describing dielectric function in the absorption onset region. The thickness decreases $\sim 7\%$ toward fcc phase. The bandgap energy of fcc phase is significantly lower than amorphous phase, $E_g^{\text{opt}}=0.53\text{eV}$ . The temperature dependent ellipsometry revealed crystallization in the range $130–150°\text{C}$ . The bandgap energy of amorphous phase possesses temperature redshift $-0.57\text{meV}/\text{K}$ $\left(30–110°\text{C}\right)$ . The crystalline phase has more complex bandgap energy shift, first $+0.62\text{meV}/\text{K}$ $\left(150–180°\text{C}\right)$ followed by $-0.29\text{meV}/\text{K}$ $\left(190–220°\text{C}\right)$ . The optical properties (refractive index, extinction coefficient, and optical bandgap energy) of as-prepared and fcc flash evaporated ${\text{Ge}}_2{\text{Sb}}_2{\text{Te}}_5$ thin films are very similar to those values previously reported for sputtered thin films.

The influence of cryothermal treatment on the mechanical properties of metallic glasses with different compositions was investigated in the present work. It was found that cryothermal cycling can induce rejuvenation as well as relaxation of the metallic glasses. The local apparent Young’s modulus and its spatial distribution width on the surface of the metallic glass increase after cryothermal cycling, while in the bulk the effect depends on the glass composition. It appeared that this increase is temporary and disappears after a period of room temperature aging. This effect is connected with a large distribution of relaxation times in the metallic glasses due to their heterogeneous structure and the formation of complex native oxides on the outer surfaces of the glasses. Our findings reveal that a cryothermal cycling treatment can improve or degrade the plasticity of a metallic glass, and the atomic bond structure appears to be very important for the outcome of the treatment.

Control of the optical behavior of active materials through manipulation of their microstructure has led to the development of high-performance photonic devices with enhanced integration density, improved quantum efficiencies and controllable color output. However, the achievement of robust light-harvesting materials with tunable, broadband and flattened emission remains a long-standing goal owing to the limited inhomogeneous broadening in ordinary hosts. Here, we describe an effective strategy for the management of photon emission by manipulating the mesoscale heterogeneities in optically active materials. Importantly, this unique approach enables control of dopant–dopant and dopant–host interactions on the extended mesoscale. This allows the generation of intriguing optical phenomena such as a high activation ratio of the dopant (close to 100%), dramatically inhomogeneous broadening (up to 480 nm), notable emission enhancement and, moreover, simultaneously extension of the emission bandwidth and flattening of the spectral shape in glass and fiber. Our results highlight that the findings connect the understanding of and manipulation in the mesoscale realm to functional behavior on the macroscale, and the approach to manage the dopants based on mesoscale engineering may provide new opportunities for the construction of a robust fiber light source.