Solution-processed hybrid perovskite of CH3NH3PbI3 (MAPbI3) exhibits an abnormal luminescence behavior at around the tetragonal-orthorhombic phase transition temperature. The combination of time resolved photoluminescence (PL), variable excitation power PL, and variable-temperature X-ray diffraction (XRD) allows us to clearly interpret the abnormal luminescence features in the phase transition region of MAPbI3. Both PL and XRD results unambiguously prove the coexistence of the tetragonal and orthorhombic phases of MAPbI3 in the temperature range of 150 to 130 K. The two luminescence features observed in the orthorhombic phase at T < 130 K originate from free excitons and donor-acceptor-pair (DAP) transitions, respectively. The comprehensive understanding of optical properties upon phase transition in MAPbI3 will benefit the development of new optoelectronic devices.

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In this paper, we report distinct enhancement of surface-state emissions (SSEs) of colloidal CdSe quantum dots (QDs) via coupling to localized plasmons (LPs) in Ag nanostructures. The roles of oleic acid (OA) ligand on QDs in the formation of Ag nanostructures and in the intense enhancement of SSEs of CdSe QDs are explored. We find that OA ligand on CdSe QDs plays a critical role in modifying the morphology of the contacted Ag, which consequently impacts the coupling of QD emitters with LPs in Ag. A systematic study of size effect of QDs on coupling of SSEs with LPs shows that as-deposited small Ag particles favorably enhance the SSEs of small-size CdSe QDs. The OA ligand on QDs yields better Ag crystallinity and clear corners during the annealing process; therefore, it promotes reshaping of small Ag particles into larger ones, favorable to enhance the SSEs of large-size CdSe QDs. The annealed QDs/Ag hybrid structures are more stable than the unannealed ones due to the loss of the OA ligand in the heating process. The selective coupling of QD emitters with LPs in Ag nanostructures allows feasible realization of microscale fluorescent color patterns. The approach of OA-assisted modification of plasmonic properties of Ag nanostructures provides a new route to synthesizing bright luminescence materials and devices that use colloidal QDs.