  Colloidal Cadmium Selenide (CdSe) nanoplatelets (NPLs) are a recently
developed class of efficient luminescent nanomaterial suitable for
optoelectronic device applications. A change in temperature greatly affects
their electronic bandstructure and luminescence properties. It is important to
understand how-and-why the characteristics of NPLs are influenced, particularly
at elevated temperature, where both reversible and irreversible quenching
processes come into picture. Here we present a study on the effect of elevated
temperature on the characteristics of colloidal CdSe NPLs. We used an
effective-mass envelope function theory based 8-band k$\cdot$p model and
density-matrix theory considering exciton-phonon interaction. We observed the
photoluminescence (PL) spectra at various temperatures for their photon
emission energy, PL linewidth and intensity by considering the exciton-phonon
interaction with both acoustic and optical phonons using Bose-Einstein
statistical factors. With rise in temperature we observed a fall in the
transition energy (emission redshift), matrix element, Fermi factor and quasi
Fermi separation, with reduction in intraband state gaps and increased
interband coupling. Also, there was a fall in the PL intensity, along with
spectral broadening due to an intraband scattering effect. The predicted
transition energy values and simulated PL spectra at varying temperatures
exhibit appreciable consistency with experimental results. Our findings have
important implications for application of NPLs in optoelectronic devices, such
as NPL lasers and LEDs, operating much above room temperature.
