Luminescence Line Broadening of CdSe Nanoplatelets and Quantum Dots for Application in w-LEDs

Abstract

Nanoplatelets (NPLs) of CdSe are an emerging class of luminescent materials, combining tunable and narrow emission bands with high quantum yields. This is promising for application in white light LEDs (w-LEDs) and displays. The origin of the narrow spectral width of exciton emission in core NPL compared to core-shell NPL and quantum dot (QD) emission is not fully understood. Here we investigate and compare temperature-dependent emission spectra of core and core-shell CdSe NPLs and QDs. A wide temperature range, 4-423 K, is chosen to gain insight into contributions from homogeneous and inhomogeneous broadening and also to extend measurements into a temperature regime that is relevant for operating conditions in w-LEDs (T ≈ 423 K). The results show that temperature-induced homogeneous broadening does not strongly vary between the various CdSe nanostructures (ΔEhom ≈ 60-80 meV at 423 K) indicating that electron-phonon coupling strengths are similar. Only for the smallest QDs is stronger coupling observed. The origin of the narrow bandwidth reported at 300 K for core CdSe NPLs is attributed to a very narrow inhomogeneous line width. At 423 K, the spectral width of NPL exciton emission is still narrower than that of QDs. A comparison with traditional w-LED phosphors is made to outline advantages (tunability, narrow bandwidth, high efficiency) and disadvantages (color shift, stability issues) of NPLs for application in w-LEDs.