The lattice dynamic and elastic instabilities of zincblende (ZB) thallium nitride (TlN) under hydrostatic pressure are extensively studied to reveal the physically driven mechanism of phase transition from the ZB to a rocksalt structure using pseudopotential plane-wave density functional calculations within the local density approximation.Our calculated results shows that both transverse acoustic phonon mode softening behavior and elastic instability are responsible for the pressure-induced structural phase transition in ZB TlN.Recently,thallium nitride (TlN) was predicted to have a small or even negative energy gap,indicating a semi-metallic character.Thus the combination of thallium with other wide-gap ⅢA-nitrides yields interesting novel teary semiconducting alloys such as Al1-xTlxN,[1] and Ga1-xTlxN,[2] whose phonon energies can encompass the near-infrared region extending well into the ultraviolet spectral range,with great potential in optical communication systems.