1.6 μm emission originated from ${\mathrm{Pr}}^{\mathrm{3+}}{\mathrm{: (}}^3{F}_3{,}^3{F}_4{\mathrm{)\to }}^3{H}_4$ transition in ${\mathrm{Pr}}^{\mathrm{3+}}$ - and ${\mathrm{Pr}}^{\mathrm{3+}}{\mathrm{/Er}}^{\mathrm{3+}}$ -doped selenide glasses were investigated under an optical pump of a conventional 1480 nm laser diode. The measured peak wavelength and full width at half maximum of the fluorescent emission were $\text{∼1650}$ and $\text{>100\hspace{0.05em}}\mathrm{nm},$ respectively. A moderate lifetime of the thermally coupled upper manifolds $\text{(∼212±5\hspace{0.05em}μ}\mathrm{s})$ together with a high stimulated emission cross section of ${\text{∼(3±1)×10}}^{\text{−20}} {\mathrm{cm}}^{\mathrm{2}}$ promises to be useful for 1.6 μm band fiber-optic amplifier that can be pumped with an existing high-power laser diode. Codoping of ${\mathrm{Er}}^{\mathrm{3+}}$ significantly enhanced the emission intensity by way of a nonradiative ${\mathrm{Er}}^{\mathrm{3+}}{\mathrm{: }}^4{I}_{\text{13/2}}\to {\mathrm{Pr}}^{\mathrm{3+}}{\mathrm{: (}}^3{F}_3{,}^3{F}_4)$ energy transfer.

Chalcogenide glass in the ternary Ge-Sb-Se system is inherently moldable, thus being considered as a strong candidate material for use in infrared-transmitting lens applications from the viewpoint of thermal and mechanical stability. In an effort to experimentally determine compositional region suitable for the molded lens applications, we evaluate its compositional dependence of hardness. Among the constituent atoms, Ge content turns out to exert a most conspicuous correlation with hardness. This phenomenological behavior is then explained in connection with the structural evolution that Ge brings about.

A facile procedure for compositional screening of chalcogenide glass (CG) is proposed to manage its infrared transmission edge (ω_c) as well as refractive index dispersion (ν) in the long-wavelength infrared (LWIR) range. Both ω_c and ν of CG turn out to be interpretable simply in connection with its chemical composition based on a postulation that CG behaves as a single average harmonic oscillator (SAHO). In this SAHO model, ω_c is expressed as a function of molar mass and average bond energy, both of which are easily accessible for a given CG composition. Two prototypical CG-forming systems in Ge-Sb-Se and Ge-Sb-S compositions exemplify the empirical compositional dependence of ω_c, which further plays a decisive role in determining ν. Following the present approach, a set of highly dispersive CG compositions in the Ge-Sb-S system is newly unveiled together with low-dispersion Ge-Sb-Se glasses. It is then experimentally demonstrated that a doublet lens configuration consisting of convex and concave lenses with low and high ν values, respectively, is able to reduce the optical aberrations. This finding presents an opportunity that ν can be envisaged just based on the compositional ratio of CG, thus facilitating completion of the LWIR Abbe diagram.

Thermal imaging in the long-wavelength infrared (8‒12 μm) range is blooming in diverse civilian sectors. In order to meet requirements specific to these new applications, lens assembly should be advanced in terms of performance enhancement and size miniaturization as well as cost reduction. Unlike its crystalline counterparts, chalcogenide glass is not only tolerable in compositional adjustments but also viscoelastic upon mechanical loading at a proper temperature. These two merits basically allow opportunities for the compositional engineering of moldable (or imprintable) chalcogenide glasses with dissimilar optical constants. The compositional screening process needs to take into account thermomechanical properties required for the precision glass molding technique as well as optical properties prioritized for lens applications. In an effort to pave an efficient way to compositional optimization of chalcogenide glass for use as molded lens, we employ ternary Ge-Sb-Se system, i.e. a prototypical chalcogenide glass forming system. The compositional range experimentally screened for use in the molded lens applications is elucidated in terms of unempirical glass structure related parameters such as mean coordination number and average bond energy. These guidelines derived from the structural evolutions of Ge-Sb-Se glass are useful in prescreening other chalcogenide glasses that are subject to molding and/or imprinting processes.