Luogen Deng

Titanium nitride (TiN) is a promising plasmonic material with hard and abrasion-resistant specialities. In this study, a gain regime, namely, plasmon-enhanced random laser emission, is demonstrated in the Pyrromethene-597 (PM597) assisted by titanium nitride (TiN) film. For this, photoluminescence and random lasing are measured at different pumping energies from PM597/Silicon and PM597/TiN/Silicon samples. Enhanced lasing efficiency is observed in the PM597/TiN/silicon sample where a plasmon resonance is formed, which increases the energy transfer between TiN and PM597. Furthermore, the multiple scattering mediated by the TiN film also plays an important role for the lasing efficiency. It is worth mentioning that the random laser emission has a strong dependence on pump position. The study of the random laser from PM597/TiN/Silicon sample with film structure is aimed to obtain a good alternative (TiN) to replace noble metals at a lowest cost.

We compared the photoluminescence (PL) of perovskite-polymer composite films on gold nanoparticle (AuNPs) substrates without and with a buffer layer of polymethyl methacrylate (PMMA). It is found that a 1.8-fold PL enhancement can be experienced due to surface plasmons with solely AuNPs substrates. With PMMA placed between the emissive layer and AuNPs, the plasmonic effect is reduced while reflectance and interface enhanced emission is increased, which results in a final PL increase of 2-fold. Such enhancements provide potential strategies to enhance the light-emitting properties of in-situ fabricated perovskite quantum dots films for light conversion applications such as LCD backlights, silicon solar cells, and photodetectors.

Manipulation of the performance of the random lasers from dye-doped nematic liquid crystals with TiN nanoparticles in non-oriented cells is studied. The experimental results show that the introduction of TiN nanoparticles into dye-doped nematic liquid crystals significantly reduces the threshold of random lasing due to the localized surface plasmon resonance of TiN nanoparticles. The emission spectrum of random lasers can be controlled by the shape of the pump spot. The threshold of random lasers increases with the decrease of the length of pump stripe. In order to obtain the emission spectrum with fine discrete sharp peaks, the narrow pump stripe is more effective than the circular pump spot. When the pump area is more like a circle, the emission spectrum is more like an amplified spontaneous emission. The underlying mechanisms of these phenomena are discussed in detail. This study provides a promising platform for designing the high-quality and low-threshold random lasers which can be controlled by the shape of the pump spot.

Random lasers (RLs) offer new functionalities inaccessible with conventional lasers, such as an alterable shape and an easy integration with flexible optoelectronic devices. Here, we demonstrate a stretchable and threshold tunable RL by modulating the order degree of the nematic liquid crystal (NLC) that is caused by the alignment of polymer chain under tensile force. The lasing thresholds show a “U” shape curve variation trend, which is attributed to the competition between the partial orientation of the NLC molecules and the reduction of the dye and NLC densities. The results are further confirmed by the power Fourier transform (PFT) spectrum analysis. This work evokes deeper understanding of the effect of order degree on RLs and extends the applications of polymer polyvinylidene fluoride (PVDF) on tunable RLs.

Recyclable coherent random lasers assisted by plasmonic nanoparticles in DCM-PVA thin films are studied. Four DCM-PVA films with different nanoparticles are made, and the radiation characteristics of these random lasers are studied. The results show that the emission spectrum of the DCM-PVA film with Au nanoparticle of 50 nm in diameter is optimal, and its threshold is about 6.53 µJ/pulse. Underlying mechanisms are discussed in detail. Then the DCM-PVA film with Au nanoparticles of 50 nm in diameter is detached from a glass substrate and adhered to different substrates. Coherent random lasers also occur when the sample is based on different substrates. Finally, a method of making samples recyclable is proposed, and the emission spectrum of samples as a function of cycle index is studied. The results show that recyclable coherent random lasers can be realized with this method. This study provides a new way, to the best of our knowledge, to realize recyclable coherent random lasers with low-threshold.

Room temperature operated continuous-wave laser has been intensively pursed in the field of on-chip photonics. The realization of continuous-wave laser strongly relies on the development of gain materials. Up to date, there is still a huge gap between the current gain materials and commercial requirements. In this work, we demonstrate continuous-wave lasers at room-temperature using rational designed in-situ fabricated perovskite quantum dots in polyacrylonitrile films on distributed feedback cavity. The achieved threshold values are 15 W/cm2, 24 W/cm2 and 58 W/cm2 for green, red and blue lasers respectively, which are one order lower than the reported values for conventional CdSe quantum dots based continuous-wave laser. Except for the high photoluminescence quantum yields, smooth surface and high thermal conductivity of the resulting films, the key success of ultralow laser threshold can be explained to the interaction of polyacrylonitrile and perovskites induced “charge spatial separation” effects. This progress opens up a door to achieve on-chip continuous-wave lasers for photonic applications.

Photostability has been a major issue for perovskites materials. Understanding the photodegradation mechanism and suppressing it are of central importance for applications. By investigating single-dot photoluminescence (PL) spectra and lifetime of MAPbX3 (MA=CH3NH3+, X=Br, I) nanocrystals (NCs) with quantum confinement under different conditions, we identified two separate pathways in the photodegradation process. The first is the oxygen-assisted light-induced etching process (photochemistry). The second is the light-driven slow charge trapping process (photophysics), taking place even in oxygen-free environment. We clarified the role of oxygen in the photodegradation process and show how the photoinduced etching can be successfully suppressed by OSTE polymer, preventing an oxygen-assisted reaction.