Two segments of horizontally grown crystalline ZnO nanorods (NRs) connected with
an amorphous layer have been successfully and reproducibly synthesized using
one-step hydrothermal technique by controlling the growth rate. The confocal
photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different
temperatures shows intense red emission with comparably week UV emission. The
strong red emission from the twin NRs is a consequence of structural
imperfections. Both UV and red bands showed signatures of strong temperature
dependent exciton-phonon scattering. Using the intensity ratio of the UV and red
emissions, we show that the individual ZnO NRs can be used as highly sensitive
cryogenic temperature sensors below ∼175 K.