Boosting the Downconversion Luminescence of Tm3+-Doped Nanoparticles for S-Band Polymer Waveguide Amplifier.

Polymer waveguide devices have attracted increasing interest in several rapidly developing areas of broadband communications since they are easily adaptable to on-chip integration and promise low propagation losses. As a key member of the waveguide gain medium, lanthanide doped nanoparticles have been intensively studied to improve the downconversion luminescence. However, current research efforts are almost confined to erbium-doped nanoparticles and amplifiers operating at the C-band; boosting the downconversion luminescence of Tm3+ for S-band optical amplification still remains a challenge. Here we report a Tb3+-induced deactivation control to enhance Tm3+ downconversion luminescence in a stoichiometric Yb lattice without suffering from concentration quenching. We also demonstrate their potential application in an S-band waveguide amplifier and record a maximum optical gain of 18 dB at 1464 nm. Our findings provide valuable insights into the fundamental understanding of deactivation-controlled luminescence enhancement and open up a new avenue toward the development of an S-band polymer waveguide amplifier with high gain.

The effect of RNA polymerase V on 24-nt siRNA accumulation depends on DNA methylation contexts and histone modifications in rice.

RNA-directed DNA methylation (RdDM) functions in de novo methylation in CG, CHG, and CHH contexts. Here, we performed map-based cloning of OsNRPE1, which encodes the largest subunit of RNA polymerase V (Pol V), a key regulator of gene silencing and reproductive development in rice. We found that rice Pol V is required for CHH methylation on RdDM loci by transcribing long noncoding RNAs. Pol V influences the accumulation of 24-nucleotide small interfering RNAs (24-nt siRNAs) in a locus-specific manner. Biosynthesis of 24-nt siRNAs on loci with high CHH methylation levels and low CG and CHG methylation levels tends to depend on Pol V. In contrast, low methylation levels in the CHH context and high methylation levels in CG and CHG contexts predisposes 24-nt siRNA accumulation to be independent of Pol V. H3K9me1 and H3K9me2 tend to be enriched on Pol V-independent 24-nt siRNA loci, whereas various active histone modifications are enriched on Pol V-dependent 24-nt siRNA loci. DNA methylation is required for 24-nt siRNAs biosynthesis on Pol V-dependent loci but not on Pol V-independent loci. Our results reveal the function of rice Pol V for long noncoding RNA production, DNA methylation, 24-nt siRNA accumulation, and reproductive development.

Reinforcement of CHH methylation through RNA-directed DNA methylation ensures sexual reproduction in rice.

DNA methylation is an important epigenetic mark that regulates the expression of genes and transposons. RNA-directed DNA methylation (RdDM) is the main molecular pathway responsible for de novo DNA methylation in plants. Although the mechanism of RdDM has been well studied in Arabidopsis (Arabidopsis thaliana), most mutations in RdDM genes cause no remarkable developmental defects in Arabidopsis. Here, we isolated and cloned Five Elements Mountain 1 (FEM1), which encodes RNA-dependent RNA polymerase 2 (OsRDR2) in rice (Oryza sativa). Mutation in OsRDR2 abolished the accumulation of 24-nt small interfering RNAs, and consequently substantially decreased genome-wide CHH (H = A, C, or T) methylation. Moreover, male and female reproductive development was disturbed, which led to sterility in osrdr2 mutants. We discovered that OsRDR2-dependent DNA methylation may regulate the expression of multiple key genes involved in stamen development, meiosis, and pollen viability. In wild-type (WT) plants but not in osrdr2 mutants, genome-wide CHH methylation levels were greater in panicles, stamens, and pistils than in seedlings. The global increase of CHH methylation in reproductive organs of the WT was mainly explained by the enhancement of RdDM activity, which includes OsRDR2 activity. Our results, which revealed a global increase in CHH methylation through enhancement of RdDM activity in reproductive organs, suggest a crucial role for OsRDR2 in the sexual reproduction of rice.

Orthogonal Trichromatic Upconversion with High Color Purity in Core-Shell Nanoparticles for a Full-Color Display.

Materials with tunable emission colors has attracted increasing interest in both fundamental research and applications. As a key member of light-emitting materials family, lanthanide doped upconversion nanoparticles (UCNPs) have been intensively demonstrated to emit light in any color upon near-infrared excitation. However, realizing the trichromatic emission in UCNPs with a fixed composition remains a great challenge. Here, without excitation pulsed modulation and three different near-infrared pumping, we report an experimental design to fine-control emission in the full color gamut from core-shell-structured UCNPs by manipulating the energy migration through dual-channel pump scheme. We also demonstrate their potential application in full-color display. These findings may benefit the future development of convenient and versatile optical methos for multicolor tuning and open up the possibility of constructing full-color volumetric display systems with high spatiotemporal resolution.

Energy Flux Manipulation in Upconversion Nanosystems.

Lanthanide-doped upconversion nanoparticles (UCNPs) exhibit unique optical characteristics, including a large anti-Stokes shift, a long luminescence lifetime, sharp emission bands, and high photostability. These virtues make UCNPs highly useful in many emerging applications such as biolabeling, security, multicolor displays, and optogenetics. Despite the enticing prospects of UCNPs, their practical utility is greatly hindered by the low efficiency of the conversion from near-infrared (NIR) excitation to visible emission. In a typical nanosystem codoped with sensitizers and activators, upconversion processes occur through NIR light sensitization, energy transfer from sensitizers to activators, sequential energy population at the excited states of the activators, and eventually the release of higher-energy photons. In fact, in the upconversion nanosystem, each step in the energy flux, including NIR energy injection, energy transfer and migration, and energy dissipation, has a decisive effect on the resulting luminescence intensity. Important in-depth studies have been conducted in pursuit of brighter UCNPs. Specifically, lanthanide ions possessing larger absorption cross sections (Nd3+) or organic dye molecules have been chosen as NIR light sensitizers to improve the light harvesting ability of upconversion nanostructures. The doping concentration and spatial distribution of lanthanide ions are strictly managed to mitigate detrimental energy cross-talk processes. The surfaces of UCNPs are passivated with epitaxially grown layers to block surface quenching. Therefore, rational design of energy flux manipulation, through control of excitation energy collection, transmission, and release in a three-dimensional nanospace of UCNPs, is crucial in constructing nanosystems with high upconversion efficiencies. In this Account, from an energy flux manipulation perspective, we attempt to provide an overview of general and emerging strategies for the design of efficient lanthanide-mediated photon upconversion nanosystems. With the significant progress made over the past several years, we are now able to design a series of upconversion nanoplatforms with efficient NIR light harvesting ability, sufficient energy transmission channels, and low levels of luminescence quenching at the particle's surface. In addition to providing a deep understanding of the underlying mechanism of energy flux, these discoveries will guide the development of upconversion nanosystems with significantly improved performance. The key aspects of this Account of energy flux manipulation in upconversion nanosystems mainly include the management of NIR photon energy injection, the optimization of efficient energy transfer pathways, and the minimization of energy flux leakage. Future challenges and opportunities for the development of efficient upconversion nanosystems are also discussed.

Remote manipulation of upconversion luminescence.

The precise control over the luminescence profile of lanthanide-doped upconversion nanomaterials is of fundamental importance for their applications in wide-ranging fields of research. Conventional chemical approaches can lead to color-tunable emissions, but they generally require stringent modification either on dopant composition or doping concentration. In this Tutorial Review, we highlight a number of complementary methods that offer remote dynamic modulation of upconversion luminescence across the visible spectrum. This review serves to provide a summary of existing guidelines for controlling the emission spectrum of upconversion nanocrystals with fixed materials composition. The review will also discuss the major approaches to manipulating excitation energies and consider likely research challenges for further development of the field at the interface between nanotechnology and biological science.

Visualization of Intra-neuronal Motor Protein Transport through Upconversion Microscopy.

Cargo transport along axons, a physiological process mediated by motor proteins, is essential for neuronal function and survival. A current limitation in the study of axonal transport is the lack of a robust imaging technique with a high spatiotemporal resolution to visualize and quantify the movement of motor proteins in real-time and in different depth planes. Herein, we present a dynamic imaging technique that fully exploits the characteristics of upconversion nanoparticles. This technique can be used as a microscopic probe for the quantitative in situ tracking of retrograde transport neurons with single-particle resolution in multilayered cultures. This study may provide a powerful tool to reveal dynamic neuronal activity and intra-axonal transport function as well as any associated neurodegenerative diseases resulting from mutation or impairment in the axonal transport machinery.

Five-photon UV upconversion emissions of Er³âº for temperature sensing.

Under 980 nm excitation, the temperature dependence of five-photon UV (256 and 276 nm) upconversion luminescence in Yb³âº-Er³âº codoped ß-NaLuF4 nanocrystals was studied from 303 K to 523 K. The 4D(7/2) and 4G(9/2) levels of Er³âº are confirmed to be thermally coupled levels. They are the highest energy states for optical thermometry known so far. By using fluorescence intensity ratio technique, optical temperature sensing characteristics based on the 4D(7/2)/4G(9/2) → 4I(15/2) transitions of Er³âº were reported here for the first time. The obtained sensitivity of this UV-based sensor is higher than that of green-based optical thermometer in low temperature range.

Luminescent CePO4:Tb colloids for H2O2 and glucose sensing.

Hydrogen peroxide (H2O2) is an essential molecule in intracellular signaling transduction and normal cell functions. It is critical to be able to detect H2O2 quantitatively in cellular processes for getting useful physiological information. Herein, we developed a novel fluorescent probe for H2O2 sensing, CePO4:Tb colloidal solution. Upon addition of H2O2, the luminescence of the colloidal CePO4:Tb solution responds linearly in a wide H2O2 concentration range of 0-200 µM, allowing for quantitative detection of H2O2. The H2O2 sensing by this method exhibits a rapid response within several minutes, a detection limit of 1.03 µM H2O2, and a relative standard deviation lower than 3.1%. This sensing material for H2O2 is also suitable for the detection of glucose since H2O2 is generated via the catalytic oxidation of glucose by oxidase enzymes. In addition to a wide linear response, a low detection limit and a high reproducibility, our present method for glucose sensing shows a highly specific response to glucose in a mixed carbohydrate solution due to the specificity of glucose oxidase to glucose. This lanthanide-based fluorescent sensing material might have potential for detecting H2O2 and glucose in biological applications.

Oleic acid-modified LiYF4:Er,Yb nanocrystals for potential optical-amplification applications.

LiYF4:18%Yb, 2%Er nanocrystals and NaYF4:18%Yb,2% Er nanoparticles (NCs) were synthesized by a solvothermal approach using oleic acid (OA) as the surfactant. With the excitation of a 980 nm diode laser, LiYF4:18%Yb, 2%Er NCs exhibit more strong emission than alpha-NaYF4:18%Yb, 2%Er at around 1530 nm. The TEM images showed that the LiYF4:18%Yb, 2%Er NCs have a nearly spherical shape and the size is about 15 nm. The OA-capped LiYF4 NCs have excellent dispersibility in organic solvents. These results showed that LiYF4:18%Yb, 2%Er NCs are a promising material for polymer-based optical waveguide amplifiers.

Upconversion luminescence properties of Yb3+ and Tm3+ codoped amorphous fluoride ZrF4-BaF2-LaF3-AlF3-NaF thin film prepared by pulsed laser deposition.

The Yb3+ and Tm3+ co-doped 55.98ZrF4-28BaF2-2.5LaF3-4AlF3-7NaF-2.5YbF3-0.02TmF3 amorphous fluoride film was prepared by pulsed laser deposition. The spectroscopic properties and energy transfer analysis of this film were studies in detail. Ultraviolet and visible upconversion emissions were observed under the infrared excitation at 980 nm. In comparison with that of its target, the upconversion emissions of the film in the visible and ultraviolet range were greatly enhanced. The possible energy transfer mechanism of the emissions was given to understand the upconversion process. This kind of thin films has potential applications for the integrated optical waveguide amplifier and ultraviolet laser.

Tandem Photon Avalanches for Various Nanoscale Emitters with Optical Nonlinearity up to 41st-Order through Interfacial Energy Transfer.

Photon avalanche has received continuous attention owing to its superior nonlinear dynamics and promising advanced applications. However, its impact is limited due to the intrinsic energy levels as well as the harsh requirements for the composites and sizes of doped materials. Here, with a universal mechanism named tandem photon avalanche (TPA), giant optical nonlinear response up to 41st-order in erbium ions, one of the most important lanthanide emitters, has been achieved on the nanoscale through interfacial energy transfer process. After capturing energy directly from the avalanched energy state 3 H4 of Tm3+ (800-nm emission), erbium ions also exhibit bright green and red PA emissions with intensities comparable to that of Tm3+ at a low excitation threshold (7.1 kWcm-2 ). Using the same strategy, effective PA looping cycles are successfully activated in Ce3+ and Ho3+ . Additionally, Yb3+ -mediated networks are constructed to further propagate PA effects to lowly-doped Tm3+ , enabling 475-nm PA emission. The newly proposed TPA strategy provides a facile route for generating photon avalanche not only from erbium ions but also from various emitters in multilayered core-shell nanoparticles.

High-Performance X-Ray Imaging using Lanthanide Metal-Organic Frameworks.

Scintillating materials that convert ionizing radiation into low-energy photons hold great potential for radiation detection, nondestructive inspection, medical radiography, and space exploration. However, organic scintillators are characterized by low radioluminescence, while bulky inorganic scintillators are not suitable for the development of flexible detectors. Here, high-resolution X-ray imaging using solution-processable lanthanide-based metal-organic frameworks as microscale scintillators is demonstrated. Mechanistic studies suggest that lanthanide ions absorb X-rays to generate high-density molecular triplet excitons, and excited linkers subsequently sensitize lanthanide ions via nonradiative resonance energy transfer. Furthermore, the crystalline nature offers a delocalized electronic feature rather than isolated subunits, which enables direct trapping of charge carriers by lanthanide emitters. By controlling the concentration ratio between Tb3+ and Eu3+ ions, efficient and color-tunable radioluminescence of lanthanide ions can be achieved. When coupled with elastic, transparent polymer matrices, these metal-organic framework-based microscintillators allow the fabrication of flexible X-ray detectors. Such detectors feature a detection limit of 23 nGy s-1 , which is 240 times lower than the typical radiation dose for medical diagnosis. X-ray imaging with resolution higher than 16.6 line pairs per millimeter is further demonstrated. These findings provide insight into the future design of hybrid scintillators for optoelectronics and X-ray sensing and imaging.

Root-associated fungal microbiota of the perennial sweet sorghum cultivar under field growth.

Root-associated fungal microbiota, which inhabit the rhizosphere, rhizoplane and endosphere, have a profound impact on plant growth and development. Sorghum bicolor (L.) Moench, also called broomcorn or sweet sorghum, is a multipurpose crop. The comparison between annual and perennial sweet sorghum cultivars in terms of plant growth, as well as their interactions with belowground fungal microbiota, is still poorly understood, although there has been growing interest in the mutualism between annual sweet sorghum and soil bacteria or bacterial endophytes. In this study, the perennial sweet sorghum cultivar N778 (N778 simply) and its control lines TP213 and TP60 were designed to grow under natural field conditions. Bulk soil, rhizosphere soil and sorghum roots were collected at the blooming and maturity stages, and then the fungal microbiota of those samples were characterized by high-throughput sequencing of the fungal ITS1 amplicon. Our results revealed that the alpha diversity of the fungal microbiota in rhizosphere soil and root samples was significantly different between N778 and the two control lines TP213 and TP60 at the blooming or maturity stage. Moreover, beta diversity in rhizosphere soil of N778 was distinct from those of TP213 and TP60, while beta diversity in root samples of N778 was distinct from those of TP213 but not TP60 by PCoA based on Bray-Curtis and WUF distance metrics. Furthermore, linear discriminant analysis (LDA) and multiple group comparisons revealed that OTU4372, a completely unclassified taxon but with symbiotroph mode, was enriched in sorghum roots, especially in N778 aerial roots at the blooming stage. Our results indicate that Cladosporium and Alternaria, two fungal genera in the rhizosphere soil, may also be dominant indicators of sorghum yield and protein content in addition to Fusarium at the maturity stage and imply that the perennial sweet sorghum N778 can primarily recruit dominant psychrotolerant bacterial taxa but not dominant cold-tolerant fungal taxa into its rhizosphere to support its survival below the freezing point.

Enhanced ultraviolet upconversion luminescence of Tm and Yb codoped ZrF4-BaF2-LaF3-AlF3-NaF glass.

Ultraviolet (UV) upconversion (UC) luminescence properties of Tm3+ ions sensitized by Yb3+ ions in ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass were studied in detail. Under the excitation from a 980 nm continuous wave (CW) diode laser, red, blue, and even UV emissions were observed in the fluorozirconate glass. Several fluorescence bands appeared in the UC emission spectrum from 292.8 nm to 805.8 nm. The UC emission peaks at 291 nm, 347 nm, 363 nm, 454 nm, 475 nm, 647 nm, 687 nm, and 804 nm correspond to the transitions of 1I6 --> 3H6, 1I6 --> 3F4, 1D2 --> 3H6, 1D2 --> 3F4, 1G4 --> 3H6, 1G4 --> 3F4, 3F3 --> 3H6, and 3H4 --> 3H6, respectively. Experimental results of intensity dependence of the up-converted fluorescence on the pump power indicate a five-photon excitation scheme of 1I6 energy level.

Size dependent ultraviolet upconversion in single YF3:Yb3+/Tm3+ particles.

Yb3+-Tm3+ codoped YF3 bulk material was synthesized through a facile high-temperature calcinations method. By grinding and selecting, the particles with different desired sizes in microns were obtained. Under 980 nm excitation, optical upconversion (UC) from near-infrared (NIR) to ultraviolet (UV) was studied for each group of particles for the effect of their size on UC. Comparing with the bulk sample, the micro-size particles exhibited strong ability for NIR-to-UV UC. With the particle size decreasing from 800 microm to 20 microm, their UV emission intensities increased rapidly. Two possible mechanisms were proposed and discussed for clarifying the small size effect (SSE).

Upconversion emission from Yb3+ and Tm3+ codoped NaYF4 thin film prepared by thermal evaporation.

Yb3+ and Tm3+ codoped fluoride thin film, with intense ultraviolet and visible upconversion emissions under 980 nm excitation, has been deposited on an Al2O3 ceramic substrate by thermal evaporation under high vacuum. NaY(0.835)Yb(0.15)Tm(0.015)F4 bulk material synthesized by high temperature solid-state reaction was used as target in preparing the thin film. Yb3+ and Tm3+ codoped system, which had been reported before, had been studied. Compared with the unannealed thin film, the annealed film showed better upconversion emission properties, especially in the ultraviolet region, given in the normalized upconversion emission spectra, due to the structure changed from amorphous to hexagonal NaYF4 (beta-NaYF4) during the annealing process. The upconversion mechanism of the thin film was also discussed in this paper.

Synthesis and upconversion luminescence of NaYF4:Yb, Tm/TiO2 core/shell nanoparticles with controllable shell thickness.

NaYF4:Yb, Tm/TiO2 core/shell nanoparticles were synthesized by a two-step method. First, the NaYF4:Yb, Tm nanocrystals were prepared using solvothermal technology; then, TiO2 shells were deposited on the nanocrystals by the hydrolysis of titanium ethoxide (TEOT) to form core/shell structures. By controlling the reaction time, we can adjust the thickness of TiO2 shell and thereby the weight percentage of TiO2 in the core/shell nanoparticles. The effect of shell thickness on the upconversion fluorescence of NaYF4:Yb, Tm nanocrystals was investigated in detail.

Ultraviolet upconversion fluorescence of Er3+ in Yb3+/Er3+-codoped Gd2O3 nanotubes.

Under 980 nm excitation, room-temperature ultraviolet (UV) upconversion (UC) emissions of Er3+ from the 4G(9/2), 2K(13/2), and 2P(3/2) states were observed in Gd2O3:Yb3+/Er3+ nanotubes, which were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. The experimental results exhibited that these UV emissions came from four-photon UC processes. In the Gd2O3:Yb3+/Er3+ nanocrystals, the energy transfers (ETs) from Yb3+ to Er3+ played important roles in populating the high-energy states of Er3+ ions. This material provides a possible candidate for building UV compact solid-state lasers or fiber lasers.