Transparent infrared-emitting CeF3:Yb-Er polymer nanocomposites for optical applications

Robust Strategy to Improve the Compatibility between Incorporated Upconversion Nanoparticles and the Bulk Transparent Polymer Matrix

Traditional transparent polymer nanocomposites combined with functional fluorescent inorganic nanofillers are promising for many advanced optical applications. However, the aggregation of the incorporated functional nanoparticles results in light scattering and will decrease the transparency of nanocomposites, which will restrain the application of the transparent nanocomposites. Herein, a robust synthesis strategy was proposed to modify upconversion nanoparticles (UCNPs) with polymethyl methacrylate (PMMA) to form UCNP@PMMA core@shell nanocomposites though metal-free photoinduced surface-initiated atom transfer radical polymerization (photo-SI-ATRP), and thus, the dispersity of UCNP@PMMA and the interface compatibility between the surface of UCNPs and the bulk PMMA matrix was greatly improved. The obtained PMMA nanocomposites possess high transparency and show strong upconversion photoluminescence properties, which promises great opportunities for application in 3D display and related optoelectronic fields. This strategy could also be applied to fabricate other kinds of functional transparent polymer nanocomposites with inorganic nanoparticles uniformly dispersed.

Probing the effect of straight chain fatty acids on the properties of lead-containing plexiglass

By adding saturated straight chain fatty acids into the reaction system of Pb(MAA)2 with MMA, the prepared lead-containing plexiglass possessed excellent optical properties. It may provide key techniques for fabricating γ-ray shielding plexiglasses.

Facile Fabrication of Upconversion Photoluminescent Transparent Semiaromatic Polyamide Nanocomposites Through Interfacial Chemistry Modification

Transparent upconversion photoluminescent polyamide nanocomposites were fabricated via a facile in situ polycondensation method with interfacial chemistry modification employing polyacrylic acid-functionalized upconversion nanoparticles (UCNP-PAA) as fillers and transparent semiaromatic polyamides (SAPA) as host materials. The as-prepared UCNP-PAA could be dispersed uniformly in the polyamide salt solution and the SAPA chains can be grafted to the UCNP-PAA through condensation reactions. The grafted SAPA ligand on the surface of UCNP increases the compatibility between SAPA and UCNP, thus causing uniform dispersion of the UCNP in the polyamide nanocomposites and improving the transmittance of the polyamide nanocomposites. The obtained polyamide nanocomposites are transparent and show strong green upconversion photoluminescence. This work solved the problem of the dispersity of incorporated nanoparticles and improving the transparency of nanocomposites and, more importantly, endowed the traditional engineering plastic with upconversion photoluminescent properties which can be applied in three-dimensional displays and the related solar cell field in the future.

Optimisation of monolithic nanocomposite and transparent ceramic scintillation detectors for positron emission tomography

High-resolution arrays of discrete monocrystalline scintillators used for gamma photon coincidence detection in PET are costly and complex to fabricate, and exhibit intrinsically non-uniform sensitivity with respect to emission angle. Nanocomposites and transparent ceramics are two alternative classes of scintillator materials which can be formed into large monolithic structures, and which, when coupled to optical photodetector arrays, may offer a pathway to low cost, high-sensitivity, high-resolution PET. However, due to their high optical attenuation and scattering relative to monocrystalline scintillators, these materials exhibit an inherent trade-off between detection sensitivity and the number of scintillation photons which reach the optical photodetectors. In this work, a method for optimising scintillator thickness to maximise the probability of locating the point of interaction of 511 keV photons in a monolithic scintillator within a specified error bound is proposed and evaluated for five nanocomposite materials (LaBr3:Ce-polystyrene, Gd2O3-polyvinyl toluene, LaF3:Ce-polystyrene, LaF3:Ce-oleic acid and YAG:Ce-polystyrene) and four ceramics (GAGG:Ce, GLuGAG:Ce, GYGAG:Ce and LuAG:Pr). LaF3:Ce-polystyrene and GLuGAG:Ce were the best-performing nanocomposite and ceramic materials, respectively, with maximum sensitivities of 48.8% and 67.8% for 5 mm localisation accuracy with scintillator thicknesses of 42.6 mm and 27.5 mm, respectively.

Design of Lanthanide-Doped Colloidal Nanocrystals: Applications as Phosphors, Sensors, and Photocatalysts

The unique optical characteristics of lanthanides (Ln³⁺) such as high color purity, long excited-state lifetimes, less perturbation of excited states by the crystal field environment, and the easy spectral conversion of wavelengths through upconversion and downconversion processes have caught the attention of many scientists in the recent past. To broaden the scope of using these properties, it is important to make suitable Ln³⁺-doped materials, particularly in colloidal forms. In this feature article, we discuss the different synthesis strategies for making Ln³⁺-doped nanoparticles in colloidal forms, particularly ways of functionalizing hydrophobic surfaces to hydrophilic surfaces to enhance their dispersibility and luminescence in aqueous media. We have enumerated the various strategies and sensitizers utilized to increase the luminescence of the nanoparticles. Furthermore, the use of these colloidal nanoparticle systems in sensing application by the appropriate selection of capping ligands has been discussed. In addition, we have shown how the energy transfer efficiency from Ce³⁺ to Ln³⁺ ions can be utilized for the detection of toxic metal ions and small molecules. Finally, we discuss examples where the spectral conversion ability of these materials has been used in photocatalysis and solar cell applications.

Upconversion Nanocomposite Materials With Designed Thermal Response for Optoelectronic Devices

Upconversion is a non-linear optical phenomenon by which low energy photons stimulate the emission of higher energy ones. Applications of upconversion materials are wide and cover diverse areas such as bio-imaging, solar cells, optical thermometry, displays, and anti-counterfeiting technologies, among others. When these materials are synthesized in the form of nanoparticles, the effect of temperature on the optical emissions depends critically on their size, creating new opportunities for innovation. However, it remains a challenge to achieve upconversion materials that can be easily processed for their direct application or for the manufacture of optoelectronic devices. In this work, we developed nanocomposite materials based on upconversion nanoparticles (UCNPs) dispersed in a polymer matrix of either polylactic acid or poly(methyl methacrylate). These materials can be processed from solution to form thin film multilayers, which can be patterned by applying soft-lithography techniques to produce the desired features in the micro-scale, and luminescent tracks when used as nanocomposite inks. The high homogeneity of the films, the uniform distribution of the UCNPs and the easygoing deposition process are the distinctive features of such an approach. Furthermore, the size-dependent thermal properties of UCNPs can be exploited by a proper formulation of the nanocomposites in order to develop materials with high thermal sensitivity and a thermochromic response. Here, we thus present different strategies for designing optical devices through patterning techniques, ink dispensing and multilayer stacking. By applying upconverting nanocomposites with unique thermal responses, local heating effects in designed nanostructures were observed.

Multicolor properties and applications of Ln3+ doped hierarchical NaY(WO4)2via a facile solvothermal process

A modified method to synthesise NaY(WO₄)₂:Ln³⁺ with hierarchical structure and luminescence properties was investigated in this work.

3D printing of resin composites doped with upconversion nanoparticles for anti-counterfeiting and temperature detection

Rapid prototyping (RP) techniques allow the construction of complex and sophisticated physical models based on personal needs, and the applications of the produced objects can be greatly extended by functionalizing the raw materials (e.g., resins) with components showing electrical, optical and magnetic properties. Here, we demonstrate a simple method for the realization of a three-dimensional architecture through 3D printing of organic resin doped with inorganic upconversion (UC) nanoparticles by using stereolithography technique. In our process, the wet-chemistry derived NaYF₄: RE (RE: rare earth) nanoparticles with red, green and blue UC emission were incorporated into a resin matrix. We printed out pre-designed 3D structures with high precision and examined the UC emission properties. In a proof-of-concept experiment, we demonstrate that the 3D printed objects have reliable optical anti-counterfeiting based on high concealment in daylight and multi-color UC emission excited by a near-infrared laser at 980 nm. We also show that the 3D part with UC emission can be used for ratiometric temperature sensing from 303.15 K to 463.15 K, making it possible to map the temperature distribution for studying the thermal diffusion process in complex objects.

Refractive Index Tuning of Hybrid Materials for Highly Transmissive Luminescent Lanthanide Particle-Polymer Composites

High-refractive-index ZrO₂ nanoparticles were used to tailor the refractive index of a polymer matrix to match that of luminescent lanthanide-ion-doped (La_0.92Yb_0.075Er_0.005F₃) light-emitting particles, thereby reducing scattering losses to yield highly transparent emissive composites. Photopolymerization of blends of an amine-modified poly(ether acrylate) oligomer and tailored quantities of ZrO₂ nanoparticles yielded optically transparent composites with tailored refractive indices between 1.49 and 1.69. By matching the refractive index of the matrix to that of La_0.92Yb_0.075Er_0.005F₃, composites with high transmittance (>85%) and low haze from the visible to infrared regions, bright 1530 nm optical emissions were achieved at solids loadings of La_0.92Yb_0.075Er_0.005F₃, ranging from 5 to 30 vol %. These optical results suggest that a hybrid matrix approach is a versatile strategy for the fabrication of functional luminescent optical composites of high transparency.

Low Loss Nanostructured Polymers for Chip-scale Waveguide Amplifiers

On-chip waveguide amplifiers offer higher gain in small device sizes and better integration with photonic devices than the commonly available fiber amplifiers. However, on-chip amplifiers have yet to make its way into the mainstream due to the limited availability of materials with ideal light guiding and amplification properties. A low-loss nanostructured on-chip channel polymeric waveguide amplifier was designed, characterized, fabricated and its gain experimentally measured at telecommunication wavelength. The active polymeric waveguide core comprises of NaYF₄:Yb,Er,Ce core-shell nanocrystals dispersed within a SU8 polymer, where the nanoparticle interfacial characteristics were tailored using hydrolyzed polyhedral oligomeric silsesquioxane-graft-poly(methyl methacrylate) to improve particle dispersion. Both the enhanced IR emission intensity from our nanocrystals using a tri-dopant scheme and the reduced scattering losses from our excellent particle dispersion at a high solid loading of 6.0 vol% contributed to the outstanding optical performance of our polymeric waveguide. We achieved one of the highest reported gain of 6.6 dB/cm using a relatively low coupled pump power of 80 mW. These polymeric waveguide amplifiers offer greater promise for integrated optical circuits due to their processability and integration advantages which will play a key role in the emerging areas of flexible communication and optoelectronic devices.

Reduction of Photoluminescence Quenching by Deuteration of Ytterbium-Doped Amorphous Carbon-Based Photonic Materials

In situ Yb-doped amorphous carbon thin films were grown on Si substrates at low temperatures (<200 °C) by a simple one-step RF-PEMOCVD system as a potential photonic material for direct integration with Si CMOS back end-of-line processing. Room temperature photoluminescence around 1 µm was observed via direct incorporation of optically active Yb³⁺ ions from the selected Yb(fod)₃ metal-organic compound. The partially fluorinated Yb(fod)₃ compound assists the suppression of photoluminescence quenching by substitution of C-H with C-F bonds. A four-fold enhancement of Yb photoluminescence was demonstrated via deuteration of the a-C host. The substrate temperature greatly influences the relative deposition rate of the plasma dissociated metal-organic species, and hence the concentration of the various elements. Yb and F incorporation are promoted at lower substrate temperatures, and suppressed at higher substrate temperatures. O concentration is slightly elevated at higher substrate temperatures. Photoluminescence was limited by the concentration of Yb within the film, the concentration of Yb ions in the +3 state, and the relative amount of quenching due to the various de-excitation pathways associated with the vibrational modes of the host a-C network. The observed wide full-width-at-half-maximum photoluminescence signal is a result of the variety of local bonding environments due to the a-C matrix, and the bonding of the Yb³⁺ ions to O and/or F ions as observed in the X-ray photoelectron spectroscopy analyses.

Engineering the Design of Brightly-Emitting Luminescent Nanostructured Photonic Composite Systems

Rare-earth doped infrared emitting composites have extensive applications in integrated optical devices such as fibre amplifiers and waveguides for telecommunications, remote sensing, and optoelectronics. In addition, recent advancements in infrared optical imaging systems have expanded the biomedical applications for infrared-emitting composites in diagnosis and imaging of living tissue systems both in vitro and in vivo. Composite systems combine the advantages of polymers (light weight, flexibility, good impact resistance, improved biomedical compatibility, and excellent processability) and inorganic phosphor host materials (low phonon energy, intense emissions, chemical durability, and high thermal stability). This paper provides a brief review of our research progress in the design and synthesis of luminescent photonic nanocomposite systems comprised of rare-earth doped particulates dispersed in a continuous polymeric matrix. The design of brightly-emitting rare-earth doped materials and the influence of host and dopant chemistries on the emission properties are discussed. Methods used to assess and measure the phosphors’ performance are also evaluated in this work. This paper will also examine the solvothermal synthesis method used to control the physical and chemical characteristics of the rare-earth doped particles, and how these characteristics impact the infrared optical properties. Also presented here are recent advances reported with luminescent nanocomposite systems fabricated for optical waveguides and biomedical imaging.

Luminescent nanocomposites made of finely dispersed Y3Ga5O12:Tb powder in a polymer matrix: promising candidates for optical devices

This paper reports the initial results of an original and simple method to elaborate flexible, self-standing, and thick luminescent films suitable for optical devices. PVP/Y(3)Ga(5)O(12):Tb(3+) nanocomposite films have been successfully achieved from a sol-gel derived Y(3)Ga(5)O(12):Tb(3+) powder and an alcoholic solution of poly-N-vinylpyrrolidone (PVP). The structural, morphological, and optical properties of these nanocomposite films have been studied and compared to those of a pristine PVP film and Y(3)Ga(5)O(12):Tb(3+) powder. The nanocomposite films were characterized by infrared and Raman spectroscopies as well as scanning and transmission electron microscopies (SEM and TEM) and demonstrated good dispersion of the phosphor particles within the polymer matrix via an alveolar mesostructure. The optical properties of these nanocomposites were fully characterized, and both their excitation and emission spectra and decay curves were recorded. Furthermore, photostability of the nanocomposite films and of the luminescent raw powder has been studied after exposure to an accelerated artificial photoageing at wavelengths higher than 300 nm. The elaboration process used is both tunable and applicable to a large variety of powders and polymers because it does not require any additive to form homogeneous and easily shapeable phosphor/polymer nanocomposites applicable in a large variety of optical devices such as solid-state-lighting.

Toward transparent nanocomposites based on polystyrene matrix and PMMA-grafted CeO2 nanoparticles

The association of transparent polymer and nanosized pigment particles offers attractive optical materials for various potential and existing applications. However, the particles embedded into polymers scatter light due to refractive index (RI) mismatch and reduce transparency of the resulting composite material. In this study, optical composites based on polystyrene (PS) matrix and poly(methyl methacrylate) (PMMA)-grafted CeO(2) hybrid particles were prepared. CeO(2) nanoparticles with an average diameter of 18 ± 8 nm were precipitated by treating Ce(NO(3))·6H(2)O with urea in the presence of a polymerizable surfactant, 3-methacyloxypropyltrimethoxy silane. PMMA chains were grafted on the surface of the nanoparticles upon free radical in situ solution polymerization. While blending of unmodified CeO(2) particles with PS resulted in opaque films, the transparency of the composite films was remarkably enhanced when prepared by PMMA-grafted CeO(2) hybrid particles, particularly those having a PMMA thickness of 9 nm. The improvement in transparency is presumably due to the reduction in RI mismatch between CeO(2) particles and the PS matrix when using PMMA chains at the interface.

Fabrication and characterization of rare-earth-doped nanostructures on surfaces

This article presents a simple and practical means to produce rare-earth-based nanostructures, as well as a combined characterization of structure and optical properties in situ. A nanosphere lithography strategy combined with surface chemistry enables the production of arrays of β-NaYF(4):Yb,Er nanorings inlaid in an octadecyltrichlorosilane matrix. These arrays of nanorings are produced over the entire support, such as a 1 cm(2) glass coverslip. The dimension of nanorings can be varied by changing the deposition conditions. A home-constructed, multifunctional microscope integrating atomic force microscopy, near-field scanning optical microscopy, and far-field optical microscopy and spectroscopy is utilized to characterize the nanostructures. This in situ and combined characterization is important for rare-earth-containing nanomaterials in order to correlate local structure with upconversion photoluminescence. Knowledge gained from the investigation should facilitate materials design and optimization, for instance, in the context of photovoltaic devices and biofluorescent probes.