Electrical and optical properties of bulk and quantum-well (QW) InSb/AlˣIn₁-ˣSb midinfrared light-emitting diodes (LEDs) have been investigated as a function of temperature and injection current. Measured current-voltage characteristics are rectifying across all temperatures and aluminium compositions for each of the devices. For the QWLEDs, experimentally measured emission spectra are compared to the theoretical equivalent, enabling individual optical transitions in the QW to be attributed to observable features.