Wide Range Near-Zero Thermal Quenching of Orange-Yellow Phosphor via Impeding Self-Oxidation of Eu2+ for Versatile Optoelectronic Applications.

Li2SrSiO4:Eu2+ is a promising substitute for traditional Y3Al5O12:Ce3+ (YAG:Ce3+) owing to its strong orange-yellow emission of 4f-5d transition originating from Eu2+ dopant, covering the more red-light region. However, its inevitable luminescence thermal quenching at high temperatures and the self-oxidation of Eu2+ strongly impede their applications. Their remediation remains highly challenging. Herein, an anti-self-oxidation(ASO) concept of Eu2+ in Li2SrSiO4 substrate by adding trivalent rare-earth ions (A3+: A = La, Gd, Y, Lu) for highly efficient and stable orange-yellow light emission have been proposed. A significantly increased orange-yellow emission (202% improvement) from Li2Sr0.95A0.05SiO4:Eu2+ with a wide range near-zero thermal quenching is obtained, superior to other Eu2+ activated phosphors. The presence of A3+ ions with various radii modifies the ASO degree of Eu2+ ions, achieving the tunable chemical state, composition, electronic configuration, crystal-field strength, and luminescent characteristics of the developed phosphors. For the proof of the concept, a W-LED device and a PDMS (Polydimethylsiloxane) luminescent film are fabricated, endowing excellent luminescence performance and thermal stability and the huge application prospects of Li2SrSiO4:Eu2+ in lighting and display fields.

Dual-Phase Glass Ceramics Containing ZnGa2O4:Cr3+ and NaYF4:Yb3+,Er3+ Nanocrystals for Dual-Mode Optical Thermometry.

Currently, developing luminescent materials for dual-mode optical thermometry has been becoming a rising topic, and concurrent temperature-sensitive optical parameters hold the key. Still, it is a serious challenge, since distinct activators are generally needed and energy transfer (ET) processes among activators inevitably occur, further leading to severe luminescence quenching. Herein, a spatial separation strategy is proposed for designing dual-phase glass ceramics (GCs) containing ZnGa2O4:Cr3+ and NaYF4:Yb3+,Er3+ nanocrystals (NCs) for dual-mode optical thermometry, in order to integrate diversified activators into one. Structural, morphological, and optical characterizations are examined to verify the partition of Cr3+ into ZnGa2O4 and Er3+ into the NaYF4 lattice in the dual-phase GC. Benefiting from such a spatial separation strategy, the adverse ET processes between Cr3+ and Er3+ could be cut off in the dual-phase GC, contributing to downshifting (DS) and upconversion (UC) luminescence. Furthermore, dual-mode optical thermometry is performed based on the lifetime of Cr3+ and fluorescence intensity ratio (FIR) of Er3+, with high relative sensitivities of 0.95% K-1@450 K and 1.24% K-1@303 K, respectively. It is evidenced that the dual-phase GC holds great potential for dual-mode optical thermometry, and this work also offers a prospective pathway for expanding the practical applications of GC luminescent materials.

Eu3+ Single-Doped Phosphor with Antithermal Quenching Behavior and Multicolor-Tunable Properties for Luminescence Thermometry.

To date, non-contact luminescence thermometry methods based on fluorescence intensity ratio (FIR) technology have been studied extensively. However, designing phosphors with high relative sensitivity (Sr) has become a research hotspot. In this work, Eu3+ single-doped Ca2Sb2O7:Eu3+ phosphors with a high Sr value for dual-emitting-center luminescence thermometry are developed and proposed. The anti-thermal quenching behavior of Eu3+ originating from the energy transfer (ET) of host → Eu3+ is found and proved in the designed phosphors. Interestingly, adjustable color emission from blue to orange can be achieved. Surprisingly, the degree of the anti-thermal quenching behavior of Eu3+ gradually reduces from 240 to 127% as the Eu3+ doping content increases from 0.005 to 0.05 mol, attributed to most Eu3+ being located in the low symmetrical [Ca1O8] dodecahedral site. According to the differentiable responses of the host and Eu3+ to temperature, the maximal Sr value reaches 3.369% K-1 (383 K). Moreover, the ambient temperature can be intuitively predicted by observing the emitting color. Owing to the excellent performance in optical thermometry, color-tunable properties, and outstanding acid and alkali resistance for polydimethylsiloxane (PDMS) films, the developed Eu3+ single-doped Ca2Sb2O7:Eu3+ phosphors are expected to be prospective candidates in luminescence thermometers and LED devices in various conditions.

Local Structure Modulation-Induced Highly Efficient Red-Emitting Ba2Gd1-xYxNbO6:Mn4+ Phosphors for Warm WLEDs.

Modulating the crystal field environment around the emitting ions is an effective strategy to improve the luminescence performance of the practical effective phosphor materials. Here, smaller Y3+ ions are introduced into substituting the Gd3+ sites in Ba2GdNbO6:Mn4+ phosphor to modify the optical properties, including the enhanced luminescence intensity, redshift, and longer lifetime of the Mn4+ ions. The substitution of smaller Y3+ ions leads to lattice contraction and then strengthens pressure on the local structure, enhances lattice rigidity, and suppresses nonradiative transition. Moreover, the prototype phosphor-converted light-emitting diode (LED) demonstrates a continuous change photoelectric performance with a correlated color temperature of 4883-7876 K and a color rendering index of 64.1-83.2, suggesting that it can be one of the most prospective fluorescent materials applied as a warm red component for white LEDss. Thus, the smaller ion partial substitution can provide a concise approach to modulate the crystal field environment around the emitting ions for excellent luminescence properties of phosphors toward the modern artificial light.

In situ synthesis of carbon doped porous silicon nanocomposites as high-performance anodes for lithium-ion batteries.

We demonstrate the in situ synthesis of carbon doped porous silicon (Si/C) nanocomposites by a simple thermal displacement process between Mg2Si and inorganic gas CO2 in one-step. Via the decomposition of Mg2Si, the reduction process occurred between Mg and CO2, leading the uniform doping of many distributed tiny carbon nanoparticles into Si. Meanwhile, the porous structure was formed after an acid treatment. When worked as anodes for lithium-ion batteries, the as-prepared s-porous Si/C nanocomposites exhibited good cycling stability and high-rate capability, which were superior to the porous Si and porous Si/C nanocomposites. It was revealed that the enhanced electrochemical properties could be ascribed to the novel porous structure and doped carbon nanoparticles that can buffer the volume expansion, as well as enhance the electronic conductivity of Si. The reaction mechanism was well investigated by studying the influence of reaction temperature and raw Mg2Si particle size on the morphology and component of the porous Si/C nanocomposites.

In-situ synthesis of Ni-Co-S nanoparticles embedded in novel carbon bowknots and flowers with pseudocapacitance-boosted lithium ion storage.

We design a facile approach to prepare a bimetallic transition-metal-sulphide-based 3D hierarchically-ordered porous electrode based on bimetallic metal-organic frameworks (Ni-Co-MOFs) by using confinement growth and in-situ sulphurisation techniques. In the novel resulting architectures, Ni-Co-S nanoparticles are confined in bowknot-like and flower-like carbon networks and are mechanically isolated but electronically well-connected, where the carbon networks with a honeycomb-like feature facilitate electron transfer with uninterrupted conductive channels from all sides. Moreover, these hierarchically-ordered porous structures together with internal voids can accommodate the volume expansion of the embedded Ni-Co-S nanoparticles. The pseudocapacitive behaviours displayed in the NCS@CBs and NCS@CFs occupied a significant portion in the redox processes. Because of these merits, both the as-built bowknot and flower networks show excellent electrochemical properties for lithium storage with superior rate capability and robust cycling stability (994 mAh g-1 for NCS@CBs and 888 mAh g-1 for NCS@CFs after 200 cycles). This unique 3D hierarchically-ordered structural design is believed to hold great potential applications in propagable preparation of carbon networks teamed up with sulphide nanocrystals for high energy storage.

Degree of Crystal Structure Distortion-Induced Tunable LiGaO2 Long Persistent Luminescence for Optical Information Encryption.

Tunable long persistent luminescence (LPL) phosphor materials have great potential for optoelectronic cryptographic applications. However, the mainstream techniques of modulating LPL generally have the characteristics of complex preparation processes, demanding crystal field environments, or expensive dopant ions, which restrict large-scale commercial application. Herein, we develop a simple, high-efficiency, and low-cost strategy to optimize the LPL of LiGaO2(LGO):Cu2+ by changing the sintering time to regulate the degree of crystal structure distortion. The Cu2+ as charge compensation will substantially enhance the emission intensity of LGO by a factor of 11.02 originating from the appropriate ionic size and coordination mode. Besides, the LPL time of LGO:Cu2+ can be extended effectively to 2 h by adjusting the sintering temperature and time (900 °C@24 h). The extension mechanism is that Li and Ga can be substituted for each other more easily and induce crystal structure distortion due to the special crystal structure of LGO, resulting in an optimal trap concentration in LGO:Cu2+. Thus, our findings provide a simple way to modulate long persistent luminescence and further consider their potential impact on optical information encryption.

Hydrofluoric Acid-Free Broadband Near-Infrared Phosphors K2LiMF6:Cr3+ with Zero-Thermal Quenching: Structure, Luminescence, and Application.

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are considered promising light sources for night vision, food analysis, biomedicine, and plant growth. Yet, the application potential of this technology is vulnerable to the function degradation of the phosphors used, such as thermal quenching, which needs to be addressed urgently. Herein, the NIR phosphors K2LiMF6:Cr3+ (M = Al, Ga, In) with a cubic double-perovskite structure synthesized by a green hydrofluoric acid-free hydrothermal method exhibit outstanding thermal stability. Under 450 nm excitation, the as-synthesized K2LiMF6:Cr3+ phosphors all exhibited broadband NIR emission covering 650-1000 nm peaking at 755-780 nm. The prepared K2LiAlF6:Cr3+ phosphor shows a unique zero-thermal quenching performance (I423 K/I298 K = 102%). The comprehensive effects of a wide band gap, large thermal energy barrier, weak electron-phonon coupling effect, and high structural rigidity are responsible for the suppression of thermal quenching in this material. The output power of the NIR pc-LED device reached 285 mW at 100 mA. This series of phosphors has promise in night vision and bioimaging applications.

Synergistic luminescent thermometer using co-doped Ca2GdSbO6:Mn4+/(Eu3+ or Sm3+) phosphors.

Luminescent thermometers provide a non-contact method of probing temperature with high sensitivity and response speed at the nanoscale. Synergistic photoluminescence from different activators can realize high sensitivity for luminescent thermometers by finely selecting ions with specific crystallographic sites. Herein, the more temperature-sensitive Mn4+ and the less-sensitive Eu3+ (or Sm3+) activators are co-doped into a Ca2GdSbO6 matrix to form an effective thermometer, where Mn4+ and Eu3+ (or Sm3+) ions occupy the Sb5+ and Gd3+ sites, respectively. The co-doping of Eu3+ ions or Sm3+ ions leads to lattice expansion of Ca2GdSbO6 matrix and a tuned narrow emission from deep-red to orangish-red. According to the ratio of luminescence intensity, the maximal Sa and Sr values are 0.19 K-0 (347 K) and 1.38% K-( (420 K) for Ca2GdSbO6:Mn4+/Eu3+ probe and 0.26 K-p (363 K) and 1.55% K-( (430 K) for Ca2GdSbO6:Mn4+/Sm3+ probe thermometers, respectively. In addition, thermometers based on Mn4+ emission lifetimes can provide the highest relative sensitivity of 1.47% K-s at 425 K. Thus, the highly-temperature-sensitive Ca2GdSbO6:Mn4+/(Eu3+ or Sm3+) phosphor is a promising candidate for practical luminescence thermometers.

Dual-phase glass ceramics for dual-modal optical thermometry through a spatial isolation strategy.

Glass ceramics (GCs) can be an ideal medium for dopant spatial isolation, avoiding the adverse energy transfer process. Herein, a spatial isolation strategy is proposed and fulfilled by dual-phase GCs. Structural characterization performed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), verified the successful dual-phase precipitation of tetragonal LiYF4 and cubic ZnAl2O4 nanocrystals (NCs) among aluminosilicate glasses. Impressively, it is evidenced that intense blue upconversion (UC) emission of Tm3+ and deep red DS emission can be attained simultaneously upon 980 nm NIR and 400 nm violet light excitation, respectively, owing to the extremely suppressed adverse energy transfer process between physically separated Tm3+ and Cr3+. This also suggests the partition of Yb3+ and Tm3+ into LiYF4 and Cr3+ into ZnAl2O4 respectively. In particular, optical thermometry based on the fluorescence intensity ratio (FIR) of Tm3+ and fluorescence lifetime of Cr3+ of dual-phase GCs were also performed in detail, with the maximum relative sensitivity of 1.87% K-1 at 396 K and 0.81% K-1 at 503 K, respectively. As a consequence, such a spatial isolation strategy would provide a convenient route for application in optical thermometry and extend the practical application of GC materials.

LiYF4-nanocrystal-embedded glass ceramics for upconversion: glass crystallization, optical thermometry and spectral conversion.

Glass ceramics (GCs) can perfectly integrate nanocrystals (NCs) into bulk materials. Herein, GCs containing LiYF4 NCs were fabricated via a traditional melt-quenching method and subsequent glass crystallization. Structural characterization was carried out via X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) analysis, suggesting the precipitation of LiYF4 NCs from a glass matrix. Taking Eu3+ as a structural probe, the spectrographic features provide compelling evidence for the partition of dopants. In particular, intense upconversion (UC) emission was achieved when co-doped with Yb3+ and Er3+. Temperature-dependent UC emission behaviour was also established based on the fluorescence intensity ratio (FIR) of Er3+, to study its properties for optical thermometry. Furthermore, spectral conversion was attained through cross relaxation (CR) between Ce3+ and Ho3+, tuning from green to red with various Ce3+ doping concentrations. There is evidence that LiYF4 NC-embedded GCs were favorable for UC, which may be extremely promising for optical thermometry and spectral conversion applications. This work may open up new avenues for the exploration of GC materials for expansive applications.