Jiasong Zhong

Dual-Phase Glass Ceramic: Structure, Dual-Modal Luminescence, and Temperature Sensing Behaviors

Yb(3+)/Er(3+)/Cr(3+) triply doped transparent bulk glass ceramic containing orthorhombic YF3 and cubic Ga2O3 nanocrystals was fabricated by a melt-quenching route to explore its possible application in optical thermometry with high spatial and temperature resolution. It was experimentally observed that Yb(3+)/Er(3+) ions incorporated into the precipitated YF3 nanophase, while Cr(3+) ions partitioned into the crystallized Ga2O3 nanophase after glass crystallization. Importantly, such spatial isolation strategy efficiently suppressed adverse energy transfer among different active ions. As a consequence, intense green anti-Stokes luminescence originated from Er(3+): (2)H11/2,(4)S3/2 → (4)I15/2 transitions, and deep-red Stokes luminescence transitions assigned to Cr(3+): (2)E → (4)A2 radiation were simultaneously realized. Impressively, the intermediate crystal-field environment for Cr(3+) in Ga2O3 made it possible for lifetime-based temperature sensing owing to the competition of radiation transitions from the thermally coupled Cr(3+) (2)E and (4)T2 excited states. In the meantime, the low-phonon-energy environment for Er(3+) in YF3 was beneficial for upconversion fluorescence intensity ratio-based temperature sensing via thermal population between the (2)H11/2 state and (4)S3/2 state. The Boltzmann distribution theory and the two-level kinetic model were adopted to interpret these temperature-dependent luminescence of Er(3+) and Cr(3+), respectively, which gave the highest temperature sensitivities of 0.25% K(-1) at 514 K for Er(3+) and 0.59% K(-1) at 386 K for Cr(3+).

Enhanced luminescence of Mn4+:Y3Al5O12 red phosphor via impurity doping

Currently, white light-emitting-diodes converted using Ce3+:Y3Al5O12 phosphor suffer from the shortage of red component and the easy aging of the organic silicone binder. Herein, a novel and non-rare-earth doped Mn4+:Y3Al5O12 red phosphor was synthesized by a traditional solid-state reaction. This phosphor can emit red luminescence attributed to Mn4+:2E → 4A2 spin-forbidden transition in the 600–700 nm spectral region and can be efficiently excited by both the commercially available near-ultraviolet and blue chips. Impressively, Mg2+, Ca2+, and Ge4+ dopants were found to be beneficial for enhancing Mn4+ luminescence, and the related mechanisms were systematically discussed. Furthermore, Mn4+:Y3Al5O12 embedded inorganic glass ceramic was successfully fabricated to replace the phosphor in organic silicone as the color converter, and a stacking geometric configuration by sequentially coupling a Ce3+:Y3Al5O12 glass ceramic and a Mn4+:Y3Al5O12 glass ceramic with an InGaN blue chip was designed to explore its possible application in warm white light-emitting diodes.

A review on Mn4+ activators in solids for warm white light-emitting diodes

Currently, the major commercial white light-emitting diodes consist of a blue-emitting chip and Y3Al5O12:Ce3+ yellow phosphor. However, the shortage of a red emitting component in the constructed device makes it difficult to realize warm white light with a high color-rendering index and low correlated color temperature. In this mini-review article, we provide an overview of recent progresses in developing Mn4+ doped red phosphors for promising applications in warm white light-emitting diodes. Firstly, the spectroscopic properties of Mn4+ in solids, including electronic and vibronic energy-level structures, crystal-field parameters as well as thermal stability, were briefly discussed. And then the related physical and chemical synthesis strategies were introduced in detail. Afterwards, Mn4+ doped phosphors, such as oxides, fluorides as well as glass ceramic composites, and their impact on improving the photoelectric performance of white light-emitting diodes were summarized. Finally, several challenges and perspectives for exploring novel and high-performance Mn4+ doped red phosphors will be presented.

Garnet-based Li6CaLa2Sb2O12:Eu3+ red phosphors: a potential color-converting material for warm white light-emitting diodes

To alleviate the issues of low thermal stability and high correlated color temperature, exploring an inorganic color converter with both yellow- and red-emissions to replace the conventional resin/silicone-based phosphor converter for obtaining high-power warm white light-emitting diodes is highly desired. In this study, a series of garnet-based Li6CaLa2−2xEu2xSb2O12 (x = 0.1–1.0) red phosphors have been successfully synthesized by a conventional high-temperature solid-state method. The microstructure and luminescence properties were systematically investigated by X-ray diffraction, emission/excitation spectra, luminescence lifetimes and temperature-dependent decays. The as-synthesized phosphors exhibited a highly efficient red luminescence at 611 nm corresponding to the 5D0–7F2 electric dipole transition of Eu3+, and the luminescence monotonously enhanced as the Eu3+ content was increased to 100 mol%. The absence of concentration quenching was ascribed to the large Eu3+–Eu3+ distance (7.048–7.105 A) and subsequently the hindering of unwanted energy migration among them in the Li6CaLa2Sb2O12 crystalline lattice. Impressively, the Li6CaLaEuSb2O12 phosphor showed an excellent thermal stability with only 9.7% emission loss when the recording temperature was increased from 293 K to 553 K. To evaluate the suitability of Li6CaLa2Sb2O12:Eu3+ as a red converter, both the garnet-based Y3Al5O12:Ce3+ yellow and Li6CaLa2Sb2O12:Eu3+ red phosphor co-doped glass ceramics were successfully fabricated by a low-temperature co-sintering technique. Importantly, the adverse energy transfers between Ce3+ and Eu3+ were efficiently suppressed due to the spatial separation of Ce3+ in Y3Al5O12 and Eu3+ in Li6CaLa2Sb2O12 in the crystal lattice. As a consequence, the quantum yield of the glass ceramic reached as high as 89.3%, and the constructed white light-emitting diode exhibited an optimal luminous efficacy of 101 lm W−1, a correlated color temperature of 5449 K and a color rendering index of 73.7. It is expected that the developed Li6CaLa2−2xEu2xSb2O12 red phosphors and the related glass ceramics should have potential applications in high-power warm white light-emitting diodes.

MoS2 Nanosheet-Modified CuInS2 Photocatalyst for Visible-Light-Driven Hydrogen Production from Water.

Exploiting photocatalysts respond to visible light is of huge challenge for photocatalytic H2 production. Here, we synthesize a new composite material consisting of few-layer MoS2 nanosheets grown on CuInS2 surface as an efficient photocatalyst for solar H2 generation. The photocatalytic results demonstrate that the 3 wt % MoS2 /CuInS2 photocatalyst exhibits the highest H2 generation rate of 316 μmol h(-1)  g(-1) under visible light irradiation, which is almost 28 times higher than that of CuInS2 . Importantly, the MoS2 /CuInS2 photocatalyst shows a much higher photocatalytic activity than that of Pt-loaded CuInS2 photocatalyst. The enhanced photocatalytic activities of MoS2 /CuInS2 photocatalysts can be attributed to the improved charge separation at the interface of MoS2 and CuInS2, which is demonstrated by the significant enhancement of photocurrent responses in MoS2 /CuInS2 photoelectrodes. This work presents a noble-metal-free photocatalyst that responds to visible light for solar H2 generation.

Large-scale room-temperature synthesis and optical properties of perovskite-related Cs4PbBr6 fluorophores

Currently, metal–halide perovskite semiconductors have attracted enormous attention for their excellent optical performance. However, challenging issues, such as the ability to perform large-scale synthesis as well as the thermal/moisture stability, limit their practical applications. Herein, we developed an inhomogeneous interface reaction strategy in a liquid–liquid immiscible two-phase system to realize the large-scale room temperature synthesis of novel perovskite-related Cs4PbBr6 semiconductors. Although the sizes were on the micrometer scale, the Cs4PbBr6 products exhibited bright green luminescence with a narrow line-width originating from exciton recombination confined in PbBr64− octahedra, and the photoluminescence quantum yields reached 40–45% owing to a large exciton binding energy of 222 meV. Furthermore, temperature cycling experiments demonstrated their excellent thermal stability with repeatable and reversible luminescence, and moisture-resistance experiments showed ∼65% of quantum yield loss after exposure to air for one month. Finally, a prototype white light-emitting diode device with a low correlated color temperature of 3675 K and a high color rendering index of 83 was constructed using green emissive Cs4PbBr6 and red emissive Eu2+:CaAlSiN3 phosphors, certainly indicating its promising applications in the optoelectronics field.

Tuning into blue and red: europium single-doped nano-glass-ceramics for potential application in photosynthesis

A series of SiO2–Al2O3–NaF–YF3 oxyfluoride glasses and β-YF3 nanocrystals embedded glass ceramics single-doped with europium ions were prepared by high-temperature melt-quenching to explore blue/red luminescent materials for potential application in the photosynthesis of green plants. Both Eu2+ and Eu3+ activators were demonstrated to coexist in this specially designed glass fabricated under ambient atmosphere, which can be well explained based on the optical basicity model of glass and evidenced by emission, excitation and time-resolved spectra. Furthermore, the crystallization strategy has been adopted to convert the precursor glasses into nano-glass-ceramics. As a result, Eu3+ ions partitioned into the precipitated orthorhombic YF3 nanophase, while Eu2+ ions remained in the glass matrix. Such spatial isolation of the different active ions in glass ceramics can effectively suppress adverse energy transfer between Eu2+ and Eu3+, leading to both intense Eu2+ blue and Eu3+ red emissions under ultraviolet light excitation.

Interface engineering of a noble-metal-free 2D–2D MoS2/Cu-ZnIn2S4 photocatalyst for enhanced photocatalytic H2 production

Accelerating the charge separation of semiconductor photocatalysts remains a great challenge to develop highly efficient solar-to-H2 conversion systems. Here, 2D Cu2+-doped ZnIn2S4 (Cu-ZnIn2S4) nanosheets modified with 2D MoS2 are designed and prepared via solution chemical routes. Detailed characterization reveals that the specially designed unique 2D–2D structure is critical to the high photocatalytic performance for solar H2 generation. Benefiting from the presence of a large 2D nanojunction in the 2D–2D photocatalyst, the MoS2/Cu-ZnIn2S4 has an increased contact surface area for charge transfer. The improved charge separation is demonstrated by the significant enhancement of photocurrent responses. It is found that the 2D–2D MoS2/Cu-ZnIn2S4 photocatalyst at a 6 wt% MoS2 loading amount exerts a 5463 μmol h−1 g−1 H2-evolution rate under visible light irradiation (λ > 420 nm) with an apparent quantum yield of 13.6% at wavelength λ = 420 nm in 0.1 M ascorbic acid aqueous solution. This activity far exceeds those of noble metal (such as Pt, Ru, Pd or Au) loaded-Cu-ZnIn2S4 photocatalysts. The results demonstrate that the construction of a 2D nanojunction is a promising strategy to accelerate charge separation and enhance the photocatalytic performance of semiconductor photocatalysts for solar H2 generation.

Achieving efficient Tb3+ dual-mode luminescence via Gd-sublattice-mediated energy migration in a NaGdF4 core–shell nanoarchitecture

A strategy to realize dual-mode luminescence from identical Tb3+ is provided via Gd-sublattice-mediated energy migration and core–shell engineering techniques. By optimizing the structure of a NaGdF4:Yb/Tm@NaGdF4:Ce/Tb nanoarchitecture, both upconversion and downshifting emissions, originating from 5D4 → 7F6,5,4,3 transitions of Tb3+, are achieved through Yb3+ → Tm3+ → [Gd3+]n → Tb3+ and Ce3+ → [Gd3+]n → Tb3+ energy transfer processes, respectively.

Color tunable dual-phase transparent glass ceramics for warm white light-emitting diodes

Currently, Ce3+:Y3Al5O12 phosphor converted white light-emitting diodes suffer from a deficiency of adequate red components and easy aging of the organic silicone matrix. Herein, Ce3+/Mn2+/Si4+:Y3Al5O12 phosphors were synthesized via a traditional solid-state reaction and they can emit intense red luminescence, which is attributed to the Mn2+:4T1 → 6A1 spin-forbidden transition under the excitation of blue light via efficient energy transfer from Ce3+ to Mn2+. Temperature-dependent emission spectra and luminescent decay curves evidence that Mn2+ activators partition into both the Al3+ octahedral and Y3+ dodecahedral sites, whereas the Si4+ sites located in the Al3+ tetrahedral site are charge compensators. Furthermore, inorganic Ce3+:Y3Al5O12 and Ce3+/Mn2+/Si4+:Y3Al5O12 dual-phase transparent glass ceramics were successfully fabricated via a low-temperature co-sintering technique to replace the phosphor in organic silicone as a color converter, and red to yellow tunable luminescence can be easily achieved by controlling the content of red phosphor in the glass matrix. Note that by combining the fabricated dual-phase glass ceramics with the InGaN blue chip, warm white light-emitting diodes with a superior optical performance and excellent heat-resistance stability were successfully constructed.