Morphologically controlled synthesis of colloidal upconversion nanophosphors and their shape-directed self-assembly

Abstract

We report a one-pot chemical approach for the synthesis of highly monodisperse colloidal nanophosphors displaying bright upconversion luminescence under 980 nm excitation. This general method optimizes the synthesis with initial heating rates up to 100°C∕ minute generating a rich family of nanoscale building blocks with distinct morphologies (spheres, rods, hexagonal prisms, and plates) and upconversion emission tunable through the choice of rare earth dopants. Furthermore, we employ an interfacial assembly strategy to organize these nanocrystals (NCs) into superlattices over multiple length scales facilitating the NC characterization and enabling systematic studies of shape-directed assembly. The global and local ordering of these superstructures is programmed by the precise engineering of individual NC's size and shape. This dramatically improved nanophosphor synthesis together with insights from shape-directed assembly will advance the investigation of an array of emerging biological and energy-related nanophosphor applications.doped nanocrystals | superlattice | lanthanides | luminescence R ecent advances in synthesis and controlled assembly of monodisperse colloidal nanocrystals (NCs) into superlattice structures have enabled their applications in optics (1), electronics (2), magnetic storage (3), etc. Single-and multicomponent superlattices composed of spherical NCs are increasingly studied and a rich family of structures is now accessible (4, 5), where the electronic and magnetic interactions between the constituents gives rise to new cooperative properties (6, 7). New synthetic approaches are yielding nonspherical NCs with physical properties unobtainable by simply tuning the size of the spheres (8-11), providing an even broader array of nanoscale building blocks. The size and shape dependence of NC's biological activity (12, 13) and toxicity (14) is also of intense interest. However, the challenge of precisely controlling particle shape while maintaining uniformity in size and surface functionality has limited studies of NC environmental health and safety just as it has hindered efforts to organize anisotropic building blocks and to establish methods to capture their unique properties in NC superlattice thin films.Lanthanide-doped nanophosphors are an emerging class of optical materials (15). These NCs often possess "peculiar" optical properties [e.g., quantum cutting (16) and photon upconversion (17)], allowing the management of photons that could benefit a variety of areas including biomedical imaging (18, 19) and therapy (20), photovoltaics (16, 21), solid state lighting (22), and display technologies (23). Colloidal upconversion nanophosphors (UCNPs) are capable of converting long-wavelength near-infrared excitation into short-wavelength visible emission through the long-lived, metastable excited states of the lanthanide dopants (24). In contrast to the Stokes-shifted emissions from semiconductor NCs or organic fluorophores and the multiphoton process employing fluorescent dyes, UCNPs offer several ...

Effects of surface stability on the morphological transformation of metals and metal oxides as investigated by first-principles calculations

“…The techniques for nanomaterial synthesis are the pillars of nanoscience and nanotechnology [17,18]. Nanomaterial syntheses can be fine-tuned to tailor the shape of the nanomaterials, which enables the application of nanomaterials in various fields, such as catalysis [19][20][21] electronics [22], optics [23], and magnetism [24] etc. Hence, developing a methodology for shape-controlled NC growth is a major current research direction.…”

Interfacial liquid-state surface-enhanced Raman spectroscopy

“…O riented assemblies of functional colloidal nanoparticles [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] are important for both fundamental science and technological applications. Such assemblies have been realized on two-dimensional (2D) solid substrates by utilizing evaporation-based convection 6,7 , capillary interaction 8 , electric fields 9,10 , substrate templating 11,12 and surface tailoring of nanoparticles 13,14 .…”

Nanophosphor Coatings: Technology and Applications, Opportunities and Challenges

“…The group includes various realizations of chemical precipitation (Bazzi et al, 2004;Buissette et al, 2006;Khan et al, 2008;Lebbou et al, 2005;Mutelet et al, 2011;, hydrothermal (Jacobsohn et al, 2007;Huang et al, 2012b;Riwotzki and Haase, 2001;Song et al, 2011; or solvothermal (Gong et al, 2013;Kasuya et al, 2007;Nyman et al, 2009;Vorsthove and Kynast, 2011) synthesis, thermal (Si et al, 2006;Ye et al, 2010) or microwave (Dai et al, 2011) decomposition, solgel methods (Back et al, 2012;Dhanaraj et al, 2001;Eid et al, 2005;Gupta et al, 2010;Zhang et al, 2002), inverse micelle method (Barnes et al, 2000;Hirai et al, 2004), laser ablation in liquid media (Mhin et al, 2009;, and combustion synthesis (Jacobsohn et al, 2007;Qi et al, 2002;Vu et al, 2007;Ye et al, 2009;Zhang et al, 2003), including flame-assisted spray pyrolysis, which is also capable of producing nanoparticles if the precursor solution is appropriately modified (Purwanto et al, 2008).…”