Two-Dimensional Violet Phosphorus-Derived Quantum Dots and Their Ormosil Gel Glasses as Efficient Optical Limiters

Nanoscale nonlinear optical (NLO) materials have drawn intensive interest for use in diverse optical limiting (OL) applications. In particular, two-dimensional (2D) quantum dots (QDs) have been investigated extensively as NLO materials because they exhibit fascinating fluorescence behavior, optoelectronic properties, and photothermal conversion. Herein, homogeneous violet phosphorus (VP) QDs were synthesized from bulk VP crystals via mechanical and liquid exfoliation and subsequently encapsulated in transparent and chemically stable organically modified silicate (ormosil) gel glass matrices by a facile sol–gel technique. Characterization of the VP QDs and the corresponding doped ormosil gel glasses demonstrated their successful fabrication. The NLO absorption and OL responses of the VP QDs were studied by picosecond (ps) and nanosecond (ns) open-aperture Z-scan measurements. The VP QDs presented reverse saturable absorption at both picosecond and nanosecond pulse widths. The NLO performance of the VP QDs was superior to that of bulk VP crystals and was further enhanced after introducing the QDs into an ormosil gel glass matrix. The band gaps of both the VP QDs and the ormosil gel glass were wider than the one-photon energy of the excitation laser (532 nm, 2.33 eV), so two-photon absorption was presumed to be mainly responsible for the observed nonlinear absorption. The OL threshold of the VP QD-doped ormosil gel glasses at a nanosecond pulse width was 5.32 J/cm2, which is comparable to or better than those of most recently reported OL materials, implying that these glasses show potential as OL materials to protect human eyes and optical devices from inevitable damage induced by high-power lasers. Our work reveals that VP QDs are attractive for use in nonlinear optics and offers a potential strategy for engineering 2D layered materials into a zero-dimensional form and subsequently constructing high-performance devices.