Lili Tao

Superbroadband near-IR photoluminescence from Pr3+-doped fluorotellurite glasses.

Praseodymium(Pr3+)-doped fluorotellurite glasses were synthesized and broadband photoluminescence (PL) covering a wavelength range from 1.30 to 1.67 μm was observed under both 488 and 590 nm wavelength excitations. The broadband PL emission is mainly due to the radiative transition from the manifolds Pr3+: 1D2 to 1G4. The PL line-shape, band width, and lifetime were modified by the Pr3+ dopant concentration, and a quantum efficiency as high as 73.7% was achieved with Pr3+ dopant in a low concentration of 0.05 mol%. The good spectroscopic properties were also predicted by the Judd-Ofelt analysis, which indicates a stronger asymmetry and covalent bonding between the Pr3+ sites and the matrix lifgand field. The large stimulated emission cross-section, long measured lifetime, and broad emission bandwidth confirm the potential of the Pr3+-singly doped fluorotellurite glass as broadband luminescence sources for the broadband near-infrared optical amplifications and tunable lasers.

High-responsivity UV-Vis Photodetector Based on Transferable WS2 Film Deposited by Magnetron Sputtering.

The two-dimensional layered semiconducting tungsten disulfide (WS2) film exhibits great promising prospects in the photoelectrical applications because of its unique photoelectrical conversion property. Herein, in this paper, we report the simple and scalable fabrication of homogeneous, large-size and transferable WS2 films with tens-of-nanometers thickness through magnetron sputtering and post annealing process. The produced WS2 films with low resistance (4.2 kΩ) are used to fabricate broadband sensitive photodetectors in the ultraviolet to visible region. The photodetectors exhibit excellent photoresponse properties, with a high responsivity of 53.3 A/W and a high detectivity of 1.22 × 1011 Jones at 365 nm. The strategy reported paves new way towards the large scale growth of transferable high quality, uniform WS2 films for various important applications including high performance photodetectors, solar cell, photoelectrochemical cell and so on.

Constructing Interfacial Energy Transfer for Photon Up- and Down-Conversion from Lanthanides in a Core-Shell Nanostructure.

We report a new mechanistic strategy for controlling and modifying the photon emission of lanthanides in a core-shell nanostructure by using interfacial energy transfer. By taking advantage of this mechanism with Gd(3+) as the energy donor, we have realized efficient up- and down-converted emissions from a series of lanthanide emitters (Eu(3+) , Tb(3+) , Dy(3+) , and Sm(3+) ) in these core-shell nanoparticles, which do not need a migratory host sublattice. Moreover, we have demonstrated that the Gd(3+) -mediated interfacial energy transfer, in contrast to energy migration, is the leading process contributing to the photon emission of lanthanide dopants for the NaGdF4 @NaGdF4 core-shell system. Our finding suggests a new direction for research into better control of energy transfer at the nanometer length scale, which would help to stimulate new concepts for designing and improving photon emission of the lanthanide-based luminescent materials.

Core–shell nanoarchitecture: a strategy to significantly enhance white-light upconversion of lanthanide-doped nanoparticles

We report that the upconversion white-light luminescence in ultrasmall CaF2:Yb/Tm/Ho nanoparticles has been enhanced by more than one order of magnitude through growing the Yb3+-containing NaYF4 shell. Such white-light enhancement achieved in the ultrasmall (sub-10 nm) core–shell nanocrystals is attributed to the surface protection and the efficient energy transfer from the active shell which not only protects the lanthanide emitters located in the core especially those near the surface from quenchers at the surface (e.g., defect, organic ligands, etc.) but also absorbs more excitation energy due to the additionally incorporated Yb3+ in the shell. The result suggests an effective approach to significantly improve the white-light emission of lanthanide-doped nanocrystals which show great potential in diverse industrial as well as newly emerging biomedical applications.

Superbroadband near-infrared emission and energy transfer in Pr³⁺-Er³⁺ codoped fluorotellurite glasses

We report the first demonstration of superbroadband emission extending from 1.30 to 1.68 μm in praseodymium(Pr(3+))-erbium(Er(3+)) codoped fluorotellurite glasses under 488 nm excitation. This superbroad near-infrared emission is contributed by the Pr(3+): (1)D(2)→(1)G(4) and Er(3+): (4)I(13/2)→(4)I(15/2) transitions which lead to emissions located at 1.48 and 1.53 μm, respectively. The quenching of the Pr(3+) emission resulted from the cross relaxation [(1)D(2), (3)H(4)]→[(1)G(4), (3)F(3,4)] was effectively compensated by the codoping of Er(3+). The results suggest that, other than the heavy-metal and transition-metal elements of active bismuth (Bi), nickel (Ni), chromium (Cr), etc., Pr(3+)-Er(3+) codoped system is a promising alternative for the broadband near-infrared emission covering the expanded low-loss window.

Bilayer graphene based surface passivation enhanced nano structured self-powered near-infrared photodetector.

A simple methyl-terminated (-CH(3)) surface passivation approach has been employed to enhance the performance of the bilayer graphene/Si nanohole array (BLG/SiNH array) Schottky junction based self-powered near infrared photodetector (SPNIRPD). The as-fabricated SPNIRPD exhibits high sensitivity to light at near infrared region at zero bias voltage. The I(light)/I(dark) ratio measured is 1.43 × 10(7), which is more than an order of magnitude improvement compared with the sample without passivation (~6.4 × 10(5)). Its corresponding responsivity and detectivity are 0.328 AW(-1) and 6.03 × 10(13) cmHz(1/2)W(-1), respectively. The demonstrated results have confirmed the high-performance SPNIRPD compared with the photo-detectors of similar type and its great potential application in future optoelectronic devices.

The WS2 quantum dot: preparation, characterization and its optical limiting effect in polymethylmethacrylate.

Due to the matching surface energy, WS2 quantum dots (QDs) can be obtained through direct liquid exfoliation in N-methyl-2-pyrrolidone rather than an ethanol and water mixture. Ultra-small WS2 QDs with a diameter of 2.4 nm are fabricated by an ultrasound method followed by high speed centrifugation up to 10 000 rpm. An excellent nonlinear optical (NLO) property of the WS2 QD/ polymethylmethacrylate (PMMA) composite for the nanosecond pulsed laser at both 532 and 1064 nm has been measured. Results illustrate the lower onset thresholds (F ON ), lower optical limiting thresholds (F OL ), and higher two-photon absorption coefficient (β) with respect to a higher concentration of embedded WS2 QDs into the PMMA solid state matrix for both 532 and 1064 nm.

Effect of laser illumination on the morphology and optical property of few-layer MoS2 nanosheet in NMP and PMMA

Two-dimensional (2D) materials and laser interaction is a very important research topic due to the unique properties of 2D materials, making them a promising candidate for high-power applications such as optical limiters and saturable absorbers for mode locking laser generation. In this paper, we have analysed the morphology and optical property changes of few-layer molybdenum disulfide (MoS2) nanosheet in NMP solution under the illumination of a Q-switched laser with operational wavelength of 532 and 1064 nm with respect to various laser energy densities. The experimental results show significant changes caused by the oxidization of MoS2 into molybdenum oxide (MoO3). Due to the stronger absorption in the visible range, the 532 nm wavelength has a stronger oxidization effect than the 1064 nm illumination wavelength. The nonlinear optical absorption properties of MoS2 in liquid NMP and in solid PMMA have been studied by using the z-scan technique and the results are compared. It has been shown experimentally that the nonlinear optical absorption properties of MoS2 in NMP disappeared but without changes in MoS2/PMMA composites after laser illumination. This confirms that MoS2 is much more stable within PMMA for preserving nonlinear absorption properties under high laser density illumination.

Tuning nonlinear optical absorption properties of WS2 nanosheets

To control the optical properties of two-dimensional (2D) materials is a long-standing goal, being of both fundamental and technological significance. Tuning nonlinear optical absorption (NOA) properties of 2D transition metal dichalcogenides in a cost effective way has emerged as an important research topic because of its possibility to custom design NOA properties, implying enormous applications including optical computers, communications, bioimaging, and so on. In this study, WS2 with different size and thickness distributions was fabricated. The results demonstrate that both NOA onset threshold, F(ON), and optical limiting threshold, F(OL), of WS2 under the excitation of a nanosecond pulsed laser can be tuned over a wide range by controlling its size and thickness. The F(ON) and F(OL) show a rapid decline with the decrease of size and thickness. Due to the edge and quantum confinement effect, WS2 quantum dots (2.35 nm) exhibit the lowest F(ON) (0.01 J cm(-2)) and F(OL) (0.062 J cm(-2)) among all the samples, which are comparable to the lowest threshold achieved in graphene based materials, showing great potential as NOA materials with tunable properties.

Intense near-infrared emission of 1.23 μm in erbium-doped low-phonon-energy fluorotellurite glass

Intense near-infrared emission located at 1.23 μm wavelength originating from the erbium (Er(3+)):(4)S3/2→(4)I11/2 transition is observed in Er(3+)-doped fluorotellurite glasses. This emission is mainly contributed by the relatively low phonon energy of the fluorotellurite glass host (~776 cm(-1)). Judd-Ofelt analysis indicates a strong asymmetry and covalent environment between Er(3+) ions and ligands in the host matrix. The emission cross-section was calculated to be 2.85×10(-21) cm(2) by the Füchtbauer-Ladenburg equation, and the population inversion is realized according to a simplified evaluation. The results suggest that the fluorotellurite glass system could be a promising candidate for the development of optical amplifiers and lasers operating at the relatively unexplored 1.2 μm wavelength region.