Nanoantennas Patterned by Colloidal Lithography for Enhanced Nanophosphor Light Emission

Abstract

Transparent coatings made of rare-earth doped nanocrystals, also known as nanophosphors, feature efficient photoluminescence and excellent thermal and optical stability. Herein, we demonstrate that the optical antennas prepared by colloidal lithography render thin nanophosphor films with a brighter emission. In particular, we fabricate gold nanostructures in the proximity of GdVO 4 :Eu 3+ nanophosphors by metal evaporation using a mask made of a monolayer of polymer beads arranged in a triangular lattice. Optical modes supported by the antennas can be controlled by tuning the diameter of the polymer spheres in the colloidal mask, which determines the shape of the gold nanostructure, as confirmed by numerical simulations. Confocal microscopy reveals that metallic antennas induce brighter photoluminescence at specific spatial regions of the nanophosphor film at targeted frequencies as a result of the coupling between gold nanostructures and nanophosphors. Patterning of nanophosphor thin layers with arrays of metallic antennas offers an inexpensive nanophotonic solution to develop bright emitting coatings of interest for color conversion, labeling, or anticounterfeiting.

Enhancement of upconversion photoluminescence in phosphor nanoparticle thin films using metallic nanoantennas fabricated by colloidal lithography

“…Nanoantennas were prepared according to a procedure reported elsewhere. 63 The first step in the fabrication of the metallic nanoantenna array was the preparation of the colloidal mask. The mask, consisting of a monolayer of polystyrene (PS, diameter of 720 nm) spheres arranged in a hexagonal lattice, was prepared by a wedge evaporation method.…”

“…The mask, consisting of a monolayer of polystyrene (PS, diameter of 720 nm) spheres arranged in a hexagonal lattice, was prepared by a wedge evaporation method. 63,64 Starting with an aqueous suspension of PS spheres at a concentration of 2.1%, substrates were placed at an angle of 31 with respect to the horizontal and 300 mL of the suspension was deposited. The suspension was then evaporated at room temperature (between 20-30 1C) for 48 hours at 90% humidity.…”

Effect of the effective refractive index on the radiative decay rate in nanoparticle thin films

“…S5 †), which cannot be explained by the modification of the optical environment alone. Therefore, the observed lifetime reduction results both from a modification of Γ rad according to eqn (7) and the emergence of new non-radiative decay channels. We measure the PLQY, which can be defined as the ratio between radiative and total decay rates in order to extract Γ rad from Γ tot .…”

“…2,3 Since then, a wide variety of optical materials made of dielectrics and metals, nanostructured at the scale of the targeted photon wavelength, have been used to manipulate the LDOS and thus modify the PL of nanomaterials, including semiconductor nanocrystals, organic molecules or rare earth (RE) phosphor nanoparticles. [4][5][6][7][8][9]10 However, the simplest approach to changing the LDOS of a light source is to modify the refractive index (n) of the medium in which it is embedded, which can easily be done in simple systems such as nanoparticle dispersions by using solvents with different values of n. [11][12][13][14][15][16] Indeed, an almost cubic dependence of Γ rad on the solvent refractive index has been observed, which has been classically explained by the use of local field cavity models. [17][18][19][20] Although this theoretical formalism can be applied to any luminescent nanoparticle, including dye-doped polymer beads or semiconductor quantum dots, most reported examples involve phosphor nanoparticles.…”

Effective Approach for Fabricating Highly Precise High-Curvature Structural Patterns via Air-Bubble Induction

“…In recent years, the interest in patterning techniques capable of effectively mass-producing large-area, regular, and periodic nano/micro-structures has increased rapidly. In particular, a process for fabricating regular and precise micropatterns with a three-dimensional (3D) curved structure has been developed. − Because a regular 3D curved structure can be used to control the pathway of light, selectively absorb or reflect specific wavelengths, store a specific material, and significantly increase the surface area, it can promote innovative development in various applications, such as microlenses, photovoltaic cells, biosensors, OLEDs, photonic crystals, and adhesive pads. − Various patterning techniques, such as colloidal lithography, − thermal reflow, , photolithography-based isotropic wet etching process, , and gray-scale lithography, have been reported to produce regular 3D curved structures at the micrometer scale. Colloidal lithography can implement a 3D nano/micro-pattern with a curved structure; however, this technique is limited in its application to practical industrial-scale processes.…”