Transient Time-resolved Photoluminescence Research Articles

Efficient, color-stable flexible white top-emitting organic light-emitting diodes

Flexible white top-emitting organic light-emitting diodes (WTEOLEDs) with red and blue phosphorescent dual-emitting layers were fabricated onto polyethylene terephthalate (PET) substrates. By inserting a 2-nm thin tris(phenypyrazole)iridium between the red and the blue emitters as an electron/exciton blocking layer, significant improvements on luminous efficiency and color stability were observed, reaching 9.9cd/A (3.74lm/W) and a small chromaticity change of (0.019, 0.011) in a wide luminance range of 80–5160cd/m2. The origin on color stability was explored by analyzing the electroluminescent spectra, the time-resolved transient photoluminescence decay lifetimes of phosphors, and the tunneling phenomenon. In addition, mechanical bending lifetimes in WTEOLEDs with spin-coatedpolymethylmethacrylate (PMMA) and thermally evaporated MoOx onto the PETs were respectively measured, where PMMA or MoOx is used as a surface planarization layer. Analysis indicates that the poorer lifetime of PMMA-modified WTEOLED than the MoOx-modified ones is mainly due to the low surface energy of PMMA.

Temperature and composition dependence of photoluminescence dynamics in CdSxSe1−x (0 ≤ x ≤ 1) nanobelts

CdSxSe1−x nanobelts with uniform and controllable composition are successfully fabricated by a one-step vapor-liquid-solid process. Temperature-dependent steady and time-resolved transient photoluminescence (PL) are studied for the obtained CdSxSe1−x nanobelts as well as pure CdS and CdSe nanobelts prepared in same method. For all samples, both band edge and surface state emission are found to contribute to the observed PL spectra. However, the emission originated from surface state is quite weak for CdSxSe1−x nanobelts as compared to CdS and CdSe. The reduced surface state emission in CdSxSe1−x nanobelts is ascribed to exciton localization due to random potential fluctuations. This attribution is further confirmed by the time-decay PL profiles where a very fast process of exciton transfer from interior to surface of nanobelts, observed in CdS and CdSe nanobelts, is absent for CdSxSe1−x nanobelts. These observations reveal that the surface effect of CdSxSe1−x nanobelts is less significant than that in CdS and CdSe nanobelts, which consequently leads to enhanced band-edge emission in CdSxSe1−x nanobelts.