Ultrafast Self-Crystallization of High-External-Quantum-Efficient Fluoride Phosphors for Warm White Light-Emitting Diodes

In this study, we used HF (as good solvent) to dissolve K₂GeF₆ and K₂MnF₆ and added ethanol (as poor solvent) to cause ultrafast self-crystallization of K₂GeF₆:Mn⁴⁺ crystals, which had an unprecedentedly high external quantum efficiency that reached 73%. By using the red phosphor, we achieved a high-quality warm white light-emitting diode with color-rendering index of <i>R</i>_a = 94, <i>R</i>9 = 95, luminous efficacy of 150 lm W^–1, and correlated color temperature at 3652 K. Furthermore, the good–poor solvent strategy can be used to fast synthesize other fluorides

Ultrafast Self-Crystallization of High-External-Quantum-Efficient Fluoride Phosphors for Warm White Light-Emitting Diodes

In this study, we used HF (as good solvent) to dissolve K₂GeF₆ and K₂MnF₆ and added ethanol (as poor solvent) to cause ultrafast self-crystallization of K₂GeF₆:Mn⁴⁺ crystals, which had an unprecedentedly high external quantum efficiency that reached 73%. By using the red phosphor, we achieved a high-quality warm white light-emitting diode with color-rendering index of <i>R</i>_a = 94, <i>R</i>9 = 95, luminous efficacy of 150 lm W^–1, and correlated color temperature at 3652 K. Furthermore, the good–poor solvent strategy can be used to fast synthesize other fluorides

Cation-Size-Mismatch Tuning of Photoluminescence in Oxynitride Phosphors

Red or yellow phosphors excited by a blue light-emitting diode are an efficient source of white light for everyday applications. Many solid oxides and nitrides, particularly silicon nitride-based materials such as M₂Si₅N₈ and MSi₂O₂N₂ (M = Ca, Sr, Ba), CaAlSiN₃, and SiAlON, are useful phosphor hosts with good thermal stabilities. Both oxide/nitride and various cation substitutions are commonly used to shift the emission spectrum and optimize luminescent properties, but the underlying mechanisms are not always clear. Here we show that size-mismatch between host and dopant cations tunes photoluminescence shifts systematically in M_1.95Eu_0.05Si_5–<i>x</i>Al_<i>x</i>N_8–<i>x</i>O_<i>x</i> lattices, leading to a red shift when the M = Ba and Sr host cations are larger than the Eu²⁺ dopant, but a blue shift when the M = Ca host is smaller. Size-mismatch tuning of thermal quenching is also observed. A local anion clustering mechanism in which Eu²⁺ gains excess nitride coordination in the M = Ba and Sr structures, but excess oxide in the Ca analogues, is proposed for these mismatch effects. This mechanism is predicted to be general to oxynitride materials and will be useful in tuning optical and other properties that are sensitive to local coordination environments

Plasmon-Enhanced Photodynamic Cancer Therapy by Upconversion Nanoparticles Conjugated with Au Nanorods

Photodynamic therapy (PDT) based on photosensitizers (PSs) constructed with nanomaterials has been widely applied to treat cancer. This therapy is characterized by an improved PS accumulation in tumor regions. However, challenges, such as short penetration depth of light and low extinction coefficient of PSs, limit PDT applications. In this study, a nanocomposite consisting of NaYF₄:Yb/Er upconversion nanoparticles (UCPs) conjugated with gold nanorods (Au NRs) was developed to improve the therapeutic efficiency of PDT. Methylene blue (MB) was embedded in a silica shell for plasmon-enhanced PDT. UCPs served as a light converter from near-infrared (NIR) to visible light to excite MB to generate reactive oxygen species (ROS). Au NRs could effectively enhance upconversion efficiency and ROS content through a localized surface plasmon resonance (SPR) effect. Silica shell thickness was adjusted to investigate the optimized MB loading amount, ROS production capability, and efficient distance for plasmon-enhanced ROS production. The mechanism of plasmon-enhanced PDT was verified by enhancing UC luminescence intensity through the plasmonic field and by increasing the light-harvesting capability and absorption cross section of the system. This process improved the ROS generation by comparing the exchange of Au NRs to Au nanoparticles with different SPR bands. NIR-triggered nanocomposites of UCP@SiO₂:MB-NRs were significantly confirmed by improving ROS generation and further modifying folic acid (FA) to develop an active component targeting OECM-1 oral cancer cells. Consequently, UCP@SiO₂:MB-NRs-FA could highly produce ROS and undergo efficient PDT in vitro and in vivo. The mechanism of PDT treatment by UCP@SiO₂:MB-NRs-FA was evaluated via the cell apoptosis pathway. The proposed process is a promising strategy to enhance ROS production through plasmonic field enhancement and thus achieve high PDT therapeutic efficacy

Homogeneous Catalytic Process of a Heterogeneous Ru Catalyst in Li–O₂ via X‑ray Nanodiffraction Observation

In recent years, lithium oxygen batteries (Li–O2) have received considerable research attention due to their extremely high energy density. However, the poor conductivity and ion conductivity of the discharge product lithium peroxide (Li2O2) result in a high charging overpotential, poor cycling stability, and low charging rate. Therefore, studying and improving catalysts is a top priority. This study focuses on the commonly used heterogeneous catalyst ruthenium (Ru). The local distribution of this catalyst is controlled by using sputtering technology. Moreover, X-ray nanodiffraction is applied to observe the relationship between the decomposition of Li2O2 and the local distribution of Ru. Results show that Li2O2 decomposes homogeneously in liquid systems and heterogeneously in solid-state systems. This study finds that the catalytic effect of Ru is related to electrolyte decomposition and that its soluble byproducts act as electron acceptors or redox mediators, effectively reducing charging overpotential but also shortening the cycle life

Synergistic-Effect-Controlled CoTe₂/Carbon Nanotube Hybrid Material for Efficient Water Oxidation

In anode, electrocatalytic water splitting involves oxygen evolution reaction (OER), which is a complex and sluggish reaction, and thus the efficiency to produce hydrogen is seriously limited by OER. We report that CoTe₂ exhibits optimized OER activity for the first time. Multiwalled carbon nanotube (MWCNT) is utilized to support CoTe₂ in generating a synergistic effect to enhance OER activity and improve stability by tuning different loading amounts of CoTe₂ on CNT. In 1.0 M KOH, bare CoTe₂ needed overpotential of 323 mV to produce 10 mA/cm² with Tafel slope of 85.1 mV/dec, but CoTe₂/carbon nanotube (CNT) with optimized loading amount of CoTe₂ required only 291 mV to produce10 mA/cm² with Tafel slope of 44.2 mV/dec. X-ray absorption near edge structure (XANES) was applied to prove that an electron transfer from e_g band of CoTe₂ to CNT caused a synergistic effect. This electron transfer modulated the bond strength of oxygen-related intermediate species on the surface of catalyst and optimized OER performance. In situ XANES was used to compare CoTe₂/CNT and pristine CoTe₂ during OER. It proved the transition state of CoOOH more easily existed by adding CNT in hybrid material during OER to enhance the efficiency of OER. Moreover, bare CoTe₂ is unstable under OER, but the CoTe₂/CNT hybrid materials exhibited improved and exceptional durability by time-dependent potentiostatic electrochemical measurement for 24 h and continuous cyclic voltammetry for 1000 times. Our result suggests that this new OER electrocatalyst for OER can be applied in various water-splitting devices and can promote hydrogen economy

High-Performance Lithium-Ion Battery and Symmetric Supercapacitors Based on FeCo₂O₄ Nanoflakes Electrodes

A successive preparation of FeCo₂O₄ nanoflakes arrays on nickel foam substrates is achieved by a simple hydrothermal synthesis method. After 170 cycles, a high capacity of 905 mAh g^–1 at 200 mA g^–1 current density and very good rate capabilities are obtained for lithium-ion battery because of the 2D porous structures of the nanoflakes arrays. The distinctive structural features provide the battery with excellent electrochemical performance. The symmetric supercapacitor on nonaqueous electrolyte demonstrates high specific capacitance of 433 F g^–1 at 0.1 A g^–1 and 16.7 F g^–1 at high scan rate of 5 V s^–1 and excellent cyclic performance of 2500 cycles of charge–discharge cycling at 2 A g^–1 current density, revealing excellent long-term cyclability of the electrode even under rapid charge–discharge conditions

All-In-One Light-Tunable Borated Phosphors with Chemical and Luminescence Dynamical Control Resolution

Single-composition white-emitting phosphors with superior intrinsic properties upon excitation by ultraviolet light-emitting diodes are important constituents of next-generation light sources. Borate-based phosphors, such as NaSrBO₃:Ce³⁺ and NaCaBO₃:Ce³⁺, have stronger absorptions in the near-ultraviolet region as well as better chemical/physical stability than oxides. Energy transfer effects from sensitizer to activator caused by rare-earth ions are mainly found in the obtained photoluminescence spectra and lifetime. The interactive mechanisms of multiple dopants are ambiguous in most cases. We adjust the doping concentration in NaSrBO₃:RE (RE = Ce³⁺, Tb³⁺, Mn²⁺) to study the energy transfer effects of Ce³⁺ to Tb³⁺ and Mn²⁺ by comparing the experimental data and theoretical calculation. The vacuum-ultraviolet experimental determination of the electronic energy levels for Ce³⁺ and Tb³⁺ in the borate host regarding the 4f–5d and 4f–4f configurations are described. Evaluation of the Ce³⁺/Mn²⁺ intensity ratios as a function of Mn²⁺ concentration is based on the analysis of the luminescence dynamical process and fluorescence lifetime measurements. The results closely agree with those directly obtained from the emission spectra. Density functional calculations are performed using the generalized gradient approximation plus an on-site Coulombic interaction correction scheme to investigate the forbidden mechanism of interatomic energy transfer between the NaSrBO₃:Ce³⁺ and NaSrBO₃:Eu²⁺ systems. Results indicate that the NaSrBO₃:Ce³⁺, Tb³⁺, and Mn²⁺ phosphors can be used as a novel white-emitting component of UV radiation-excited devices

Near-Infrared-Activated Fluorescence Resonance Energy Transfer-Based Nanocomposite to Sense MMP2-Overexpressing Oral Cancer Cells

The matrix metalloproteinases (MMPs) are well-known mediators that are activated in tumor progression. MMP2 is a kind of gelatinase in extracellular matrix remodeling and cancer metastasis processes. MMP2 secretion increased in many types of cancer diseases, and its abnormal expression is associated with a poor prognosis. We fabricated a nanocomposite that sensed MMP2 expression by a red and blue light change. This nanocomposite consisted of an upconversion nanoparticle (UCNP), MMP2-sensitive peptide, and CuInS₂/ZnS quantum dot (CIS/ZnS QD). An UCNP is composed of NaYF₄:Tm/Yb@NaYF₄:Nd/Yb, which has multiple emissions at UV/blue-visible wavelengths under 808 nm laser excitation. The conjugated CIS/ZnS QD showed the red-visible fluorescence though the FRET process. The two fluorophores were connected by a MMP2-sensitive peptide to form a novel MMP2 biosensor, named UCNP@p-QD. UCNP@p-QD was highly biocompatible according to cell viability assay. The FRET-based biosensor was employed in the MMP2 determination <i>in vitro</i> and <i>in vivo</i>. Furthermore, it was administrated into the tumor-bearing mouse to check MMP2 expression. UCNP@p-QD could be a promising tool for biological study and biomedical application. In this study, we demonstrated that the CIS/ZnS QD improved the upconversion intensity through a near-infrared-induced FRET process. This nanocomposite has the advantage of light penetration, excellent biocompatibility, and high sensitivity to sense MMP2. The near-infrared-induced composites are a potential inspiration for use in biomedical applications

Structural Ordering and Charge Variation Induced by Cation Substitution in (Sr,Ca)AlSiN₃:Eu Phosphor

Nitride phosphors are suitable for white light-emitting diode applications. In this study, the structure of phosphor has been modified through cation substitution to induce charge variation and a rearrangement of neighboring nitride clusters, and consequently enhance its luminescent behavior. Substitution of Ca²⁺ by Sr²⁺ cations expanded the lattice volume and the <i>bc</i> plane, but shortened the distance between the layers along the <i>a</i> axis. Lattice distortion of the framework introduced high-coordination sites in the Sr/Eu centers and adequate space, thereby facilitating charge variation of activators under reduced atmosphere, as detected through X-ray absorption near-edge structure spectroscopy. As such, the photoluminescent intensity of the phosphors increased by more than 10% and a blue shift occurred. The microstructures of the samples were also analyzed using high-resolution transmission electron microscopy. Cation substitution induced a special change in the anion environment, as indicated in the solid-state Raman spectra. Moreover, typical ordering variations in the SiN₄ and AlN₄ clusters are generated in the lattice. Meanwhile, neighbor sequence of (Si/Al)­N₄ around the divalent centers were observed through solid-state nuclear magnetic resonance spectroscopy. The modified ordering distribution resulted in a rigid structure and improved the thermal quenching behavior. Thermal stability has been enhanced by 10% at 473 K when <i>x</i> = 0.9 in Sr_<i>x</i>Ca_0.993‑xAlSiN₃:Eu²⁺_0.007 compared with that at <i>x</i> = 0. This study promotes the research of neighbor sequence for selective tetrahedral sites such as Li, Mg, Al, and Si coordinated by N atoms in contact with cation sites