Temperature-dependent photoluminescence of ZnSe nanocrystals ball-milled for 0–60 minutes

ZnSe nanocrystals (NCs) with sizes of several tens of nanometers have attracted renewed attention as true blue emitters in light-emitting diodes. The hydrothermal method is a preferable and cost-effective approach for producing high-quality ZnSe NCs with sizes around a hundred nanometers; therefore, subsequent size-reduction treatment becomes essential to obtain ZnSe NCs within the desirable size range of several tens of nanometers. Ball milling is a simple and effective method for reducing the size of ZnSe NCs, although it may introduce structural defects. This paper presents the temperature-dependent photoluminescence (PL) characteristics of various ZnSe NCs hydrothermally synthesized and subsequently ball-milled to assess their corresponding optical properties. The as-synthesized ZnSe NCs and those milled for 10 and 20 min show a narrow excitonic emission at 2.79 eV (∼444 nm) and broad bands at ∼2.72 eV (453 nm) and 2.46 eV (500 nm) at 20 K. Above 150 K, only the excitonic emission remains at 2.68 eV (∼463 nm), as the latter two are thermally quenched. For the 40- and 60-min milled samples, the excitonic emission is significantly weakened. Analyzing the temperature-dependent PL spectra over the 20–300 K range enables us to determine the activation energies of 70 meV, 7 meV, and 10 meV for the excitonic emission and the PL bands peaking around 2.72 eV and 2.46 eV, respectively. The possible origins of the observed PL bands are discussed.