Revealing two chemical strategies to tune bright one- and two-photon excited fluorescence of carbon nanodots

International audienceCarbon-based dots (CDs) are a novel class of luminescent carbon nanomaterials that have attracted much attention as promising alternatives for cadmium-based quantum dots and fluorescent organic dyes. Although different strategies have been proposed to produce CDs with intense and tuneable one-photon excited fluorescence (OPEF), the case of analogous two-photon excited fluorescence (TPEF) has not been fully explored yet. By varying the synthesis conditions, we produced three types of phloroglucinol-based carbon nanodots (PG CNDs). Their remarkable OPEF and TPEF properties can be tuned by (Ia) the conjugated aromatic domains and (Ib) the content of oxygenous moieties. In addition, the emission colour of the PG CNDs is strongly responsive to (II) the hydrogen-bonding network, enabling colour-switching while maintaining excellent fluorescence yields (both OPEF and TPEF). These three factors were evaluated for their suitability for the tuning of the emission colour. Our studies point out the advantages of the tuneable PG CNDs to be used in optoelectronics and biological application domains

Spectrally resolved nonlinear optical properties of doped versus undoped quasi-2D semiconductor nanocrystals : copper and silver doping provokes strong nonlinearity in colloidal CdSe nanoplatelets

Nonlinear optical processes are crucial for emerging applications including multiphoton-excited fluorescence microscopy and optical power limiting. Therefore, searching for materials of high multiphoton absorption cross sections is essential for the development of these techniques. We present synthesis of 4.5 monolayer CdSe nanoplatelets (NPLs) doped with silver and copper ions along with the evaluation of their two-photon absorption (TPA) and three-photon absorption (3PA) cross sections. Doping significantly increases the TPA cross section of each NPL sample, which reaches up to 1.33 × 107 GM for the most absorbing copper-doped ones. We also detected 1-2 orders of magnitude-enhanced 3PA cross sections for the doped NPLs in comparison with their undoped counterparts. As TPA and 3PA peaks appear, in the first and the second biological transmission windows, respectively, doped NPLs are promising candidates for multiphoton fluorescence microscopy as bioimaging agents. Moreover, the strong nonlinear response suggests application as active optoelectronic materials in optical sensors.Ministry of Education (MOE)National Research Foundation (NRF)Published versionThis work has received financial support from the National Science Centre, Poland, under grant no. 2018/29/B/ST4/ 02172, the National Research Foundation of Singapore under program NRF-NRFI2016-08, and the Singapore Ministry of Education under grant MOE-RG62/20

Determining the 3D orientation of optically trapped upconverting nanorods by in situ single-particle polarized spectroscopy

An approach to unequivocally determine the three-dimensional orientation of optically manipulated NaYF4:Er3+,Yb3+ upconverting nanorods (UCNRs) is demonstrated. Long-term immobilization of individual UCNRs inside single and multiple resonant optical traps allow for stable single UCNR spectroscopy studies. Based on the strong polarization dependent upconverted luminescence of UCNRs it is possible to unequivocally determine, in real time, their three-dimensional orientation when optically trapped. In single-beam traps, polarized single particle spectroscopy has concluded that UCNRs orientate parallel to the propagation axis of the trapping beam. On the other hand, when multiple-beam optical tweezers are used, single particle polarization spectroscopy demonstrated how full spatial control over UCNR orientation can be achieved by changing the trap-to-trap distance as well as the relative orientation between optical traps. All these results show the possibility of real time three-dimensional manipulation and tracking of anisotropic nanoparticles with wide potential application in modern nanobiophotonicsThis work was supported by the Spanish Ministerio de Educación y Ciencia (MAT2013-47395-C4-1-R) and by Banco Santander for “proyectos de cooperación interuniversitaria” (2015/ ASIA/06). Patricia Haro-González thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the Juan de la Cierva program. Paloma Rodríguez-Sevilla thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the “Promoción del talento y su Empleabilidad en I+D+i” statal program. Dominika Wawrzyńczyk, Marcin Nyk and Marek Samoć acknowledge the support from the National Science Centre under grant DEC-2012/04/M/ST5/00340, by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Technology, as well as from the Foundation for Polish Science under START 2014 programme. This work has received funding from The Royal Society (IE130466). Mark D. Mackenzie acknowledges funding from EPSRC (grant no EP/J500227/