Glass ceramics (GCs), which consist essentially of a homogeneous solid state dispersion of nanocrystals (NCs) embedded in a chemically inert and mechanically robust glass matrix, appear to be an extremely promising class of solid state materials that can be easily tailored into arbitrary shapes, including a new generation of optical fibers, for efficient incoherent and coherent sources of mid-infrared (MIR) light emission. This unique capability not only stems from the fact that one can tailor the underlying glass matrix for optimal macroscopic physical properties and ultrahigh transparency at the wavelengths of interest (resulting in appropriate “transparent glass ceramics” or TGCs), but also stems from the fact that one can embed these matrices with size and structure-tailored NCs, which in turn can be doped with relatively high concentrations of MIR emitting rare-earth or transition metal ions. This potential is tantamount to the localization of these highly efficient MIR ionic emitters into carefully selected and highly favorable “process-engineered” custom crystalline host “nanocages,” while insulating the ionic emitters from the emission-quenching glass host matrix, the latter being chosen largely because of its highly favorable macroscopic bulk properties, including its ductility and formability into near-arbitrary shapes (at appropriate temperatures). Such MIR TGCs appear to be very promising for numerous photonics applications, including compact and relatively efficient waveguide sensors, broadband incoherent MIR light sources, superluminescent light sources, advanced fiber-optic devices, and broadly wavelength-tunable and ultrashort pulse mode-locked fiber and bulk solid-state lasers. In this paper, we review past achievements in this field, starting with an overview of TGCs, followed by discussions of currently preferred methods of fabrication, characterization, and optimization of suitably doped oxyfluoride, tellurite, and chalcogenide TGCs and of our projections of anticipated future developments in this field at both the materials and device levels.

Broadband emission at 2.7 µm is observed in an E r 3 + -doped P b O − P b F 2 − B i 2 O 3 − G a 2 O 3 glass. The measured emission band full-width-at-half-maximum (FWHM) is ∼ 184.4 n m , approximately 36 nm wider than that of fluoride glasses. The 2.7 µm emission intensity is almost twice as strong as that of fluoride glasses. The peak values of emission and absorption cross-sections are calculated to be 1.54 × 10 − 20 c m 2 and 1.19 × 10 − 20 c m 2 , respectively. This oxyfluoride heavy metal glass shows potential as broadband mid-infrared emission gain material.

Compact, mechanically robust, and cost-effective mid-infrared (MIR) light sources are key components in portable and field-deployable gas sensors. Capitalizing on an efficient energy transfer mechanism between C o 2 + and F e 2 + , we have demonstrated for the first time, to the best of our knowledge, that ultrabroadband 2.5–5.5 µm MIR emission can be achieved at room temperatures in chalcogenide (ChG) glasses that are pumped by a commercially available erbium-doped fiber amplifier emitting at 1.57 µm. These MIR-transparent ChG glass ceramics are embedded with C o 2 + / F e 2 + codoped ZnSe nanocrystals, and show sufficient MIR emission intensities and bandwidths to enable gas sensing for multiple target analytes such as butane and carbon dioxide. We also describe, to the best of our knowledge, the first observation of a unique “anomalous” increase in the MIR luminescence intensity as a function of temperature.