A. Gowri Manohari

SERS-active ZnO/Ag hybrid WGM microcavity for ultrasensitive dopamine detection

Dopamine (DA) is a potential neuro modulator in the brain which influences a variety of motivated behaviors and plays a key role in life science. A hybrid ZnO/Ag microcavity based on Whispering Gallery Mode (WGM) effect has been developed for ultrasensitive detection of dopamine. Utilizing this effect of structural cavity mode, a Raman signal of R6G (5 × 10−3 M) detected by this designed surface-enhanced Raman spectroscopy (SERS)-active substrate was enhanced more than 10-fold compared with that of ZnO film/Ag substrate. Also, this hybrid microcavity substrate manifests high SERS sensitivity to rhodamine 6 G and detection limit as low as 10−12 M to DA. The Localized Surface Plasmons of Ag nanoparticles and WGM-enhanced light-matter interaction mainly contribute to the high SERS sensitivity and help to achieve a lower detection limit. This designed SERS-active substrate based on the WGM effect has the potential for detecting neurotransmitters in life science.

Crystal structure and electron transition underlying photoluminescence of methylammonium lead bromide perovskites

Bromine-based methylammonium lead hybrid perovskites (CH3NH3PbBr3 or MAPbBr3) have exhibited remarkable charge transport and optical properties. Nonetheless, the photoluminescence (PL) behavior and electronic transition state are still obscure. In this paper, the intrinsic emission mechanisms of two peaked CH3NH3PbBr3 microcuboid crystals have been investigated. A systematic analysis of the stable-state, transient-state and temperature-dependent spectra demonstrated the structure–activity relationship between optical properties and crystal phase. The lattice symmetry was also confirmed by the two-photon absorption induced PL. The findings can be assigned to the fact that the two emission states with band-energy ∼2.22 eV and ∼2.31 eV are originated from free exciton and free carrier recombination which are attributed to the coexistence of a non-centrosymmetric tetragonal phase and a centrosymmetric cubic phase for CH3NH3PbBr3 microcrystals at higher temperature (>160 K).

Energy transfer in co- and tri-doped Y3Al5O12 phosphors

Abstract Single-doped (Ce 3+ ,Tb 3+ ), co-doped (Ce 3+ -Tb 3+ , Ce 3+ -Yb 3+ , Tb 3+ -Yb 3+ ) and tri-doped (Ce 3+ -Tb 3+ -Yb 3+ ) Y 3 Al 5 O 12 phosphors were synthesized by a solid-state reaction method. The XRD, excitation and emission spectra and the fluorescence lifetime of the samples were measured. The energy transfer mechanism was also investigated. The results showed that the energy transfer efficiency from Tb 3+ to Ce 3+ was 51% and the energy transfer efficiency from Ce 3+ to Yb 3+ was 63.1%. Concomitantly, both were more efficient than that from Ce 3+ to Tb 3+ (7%) and from Tb 3+ to Yb 3+ (10.2%). Also, the Yb 3+ ions received energy mainly from Ce 3+ ions in Ce 3+ -Tb 3+ -Yb 3+ tri-doped Y 3 Al 5 O 12 phosphors. Among these materials, Ce 3+ -Yb 3+ co-doped YAG phosphors are a better choice than others as a down-conversion material due to their higher energy transfer efficiency.

Enhancement of the near-infrared emission of Ce3+–Yb3+ co-doped Y3Al5O12 phosphors by doping Bi3+ ions

Ce3+–Yb3+ co-doped Y3Al5O12 phosphors are one of most the potential candidates of down-conversion materials for photovoltaic cells. To improve the near-infrared emission from Yb3+ ions, Bi3+ ions were introduced into the phosphors. The experimental results showed that the intensity of Yb3+ emission was greatly enhanced after doping Bi3+ ions into the phosphors. This may be attributed to an additional pathway via Bi3+ ions for the energy transfer from Ce3+ to Yb3+. Different from the co-doped phosphors, where the energy of Ce3+ ions was transferred only to Yb3+ ions, in Bi3+–Ce3+–Yb3+ tri-doped phosphors, the energy of Ce3+ ions could be transferred not only to Yb3+ ions but also to Bi3+ ions. Then, Bi3+ ions transferred part of the energy to Yb3+ ions. This enabled Yb3+ ions to obtain more energy and enhance their near-infrared emission.

Lasing mode evolution and regulation of the perovskite CH3NH3PbBr3

Due to their high absorption efficiency, great carrier diffusion length, and low surface recombination velocity, lead halide perovskite micro- and nano-lasers have been extensively studied for their potential applications in optoelectronic devices and photonics integration. But it is still a challenge to achieve a stable and controllable lasing action, especially for single-mode lasing. Herein, solution-processed single-crystal CH3NH3PbBr3 perovskite microsheets and microwires were synthesized to realize Fabry–Perot lasing at room temperature. Based on their high crystalline quality and high optical confinement, the lasing actions were investigated systematically. The lasing mode regulation was carried out from multiple modes to the single mode via reducing the width of CH3NH3PbBr3 microstructures.