Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional (2D) material for photonics device due to its large bandgap and flexibility in nanophotonic circuits. Here, we report bright and localized luminescent centres can be engineered in hBN monolayers and flakes using laser irradiation. The transition from hBN to cBN emerges in laser irradiated hBN large monolayers while is absent in processed hBN flakes. Remarkably, the colour centres in hBN flakes exhibit room temperature cleaner single photon emissions with g2(0) ranging from 0.20 to 0.42, a narrower line width of 1.4 nm and higher brightness compared with monolayers. Our results pave the way to engineering deterministic defects in hBN induced by laser pulse and show great prospect for application of defects in hBN used as nano-size light source in photonics.

2Strong interactions between surface plasmons in ultra-compact nanocavities and excitons in two dimensional materials have attracted wide interests for its prospective realization of polariton devices at room temperature. Here, a continuous transition from weak coupling to strong coupling between excitons in MoS2 monolayer and highly localized plasmons in ultracompact nanoantenna is proposed. The nanoantenna is assembled by a silver nanocube positioned over a gold film and separated by a dielectric spacer layer. A 1570-fold enhancement in the photoluminescence is observed at weak coupling regime in hybrid nanocavities with thick spacer layers. The interaction between excitons and plasmons is then directly prompted to strong coupling regime by shrinking down the thickness of spacer layer. Room temperature formation of polaritons with Rabi splitting up to 190 meV is observed with a fair polariton loss around 165 meV. Numerical calculations quantify the relation between coupling strength, local density of states and spacer thickness, and reveal the transition between weak coupling and strong coupling in nanocavities. The findings in this work offer a guideline for feasible designs of plasmon-exciton interaction systems with gap plasmonic cavities.

All inorganic cesium lead halide perovskite semiconductors exhibit great potential for nanolasers, light-emitting diodes, and solar cells, because of their unique properties including low threshold, high quantum efficiency and low cost. However, the high material refractive index of perovskite semiconductors hinders light extraction efficiency for photonic and illumination applications. In this paper, we demonstrate high light extraction efficiency achieved in CsPbBr 2.75 I 0.25 two-dimensional photonic crystals. The perovskite photonic crystals exhibit both emission rate inhibition and light energy redistribution simultaneously. We observed a 7.9-fold reduction of spontaneous emission rate with a slower decay in CsPbBr 2.75 I 0.25 photonic crystals, because of the photonic bandgap effect (PBG). We also observed a 23.5-fold PL emission enhancement, as a result of light energy redistribution from 2D guided modes to vertical direction in perovskite photonic crystals thin films, indicating a high intrinsic light extraction efficiency. Such a combination of inhibiting undesirable emission with redistributing light energy into useful modes offers a new promising approach in various applications for perovskite, including solar cell, displays, and photovoltaics.

Amplified spontaneous emission of a colloidal quantum dot film is electronically controlled in a practical device.

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