Jiachi Zhang

Facile synthesis of ultrathin NiCo2S4 nano-petals inspired by blooming buds for high-performance supercapacitors

3D petal-like NiCo2S4 nanostructures have been fabricated via a simple, mild and efficient hydrothermal strategy and the growth mechanism of NiCo2S4 nano-petals has been investigated. Such NiCo2S4 nano-petal electrodes can deliver an ultrahigh specific capacitance of 2036.5 F g−1 at a current density of 1 A g−1, superior rate capability and remarkable cycle stability (94.3% of capacitance retention after 5000 cycles). The as-fabricated asymmetric supercapacitors based on NiCo2S4 nano-petals//active carbon electrodes demonstrate a high energy density of 35.6 W h kg−1 at a power density of 819.5 W kg−1, with both long-term cycling and high rate stabilities. Such supercapacitors have been tested to power ten LEDs (2.03 V, 20 mA) in series for around 60 minutes, indicating their great potential for practical application.

How to induce highly efficient long-lasting phosphorescence in a lamp with a commercial phosphor: a facile method and fundamental mechanisms

We successfully tailor the properties of a well-known commercial lamp with the Zn2SiO4:Mn2+ phosphor as a novel, highly efficient, long-lasting green phosphor by using the co-doping method. The long-lasting phosphorescence (LLP) of the optimal Zn2SiO4:Mn2+,Yb3+ sample can be recorded for approximately 30 h (0.32 mcd m−2) and is visible for even more than 60 h in the dark by using dark-adapted vision. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Several classical methods of investigation including decay curves, thermoluminescence, fading experiments, multi-peak fitting based on general-order kinetics, and first-principles calculations are used in this study to examine the LLP properties, the effects of such co-dopants and the nature of traps in detail. The important retrapping and tunneling effects, combined with a kinetics investigation, are discussed. A modified law concerning the influences of co-dopants on the traps around the Mn2+(3d5, d → d type) centers and the LLP properties are summarized. Finally, the LLP mechanism of the Zn2SiO4:Mn2+,Yb3+ phosphor is proposed.

Near-Infrared Quantum Cutting Long Persistent Luminescence.

By combining the unique features of the quantum cutting luminescence and long persistent luminescence, we design a new concept called “near-infrared quantum cutting long persistent luminescence (NQPL)”, which makes it possible for us to obtain highly efficient (>100%) near-infrared long persistent luminescence in theory. Guided by the NQPL concept, we fabricate the first NQPL phosphor Ca2Ga2GeO7:Pr3+,Yb3+. It reveals that both the two-step energy transfer of model (I) and the one-step energy transfer of model (IV) occur in 3P0 levels of Pr3+. Although the actual efficiency is not sufficient for the practical application at this primitive stage, this discovery and the associated materials are still expected to have important implications for several fields such as crystalline Si solar cells and bio-medical imaging.

How to design ultraviolet emitting persistent materials for potential multifunctional applications: a living example of a NaLuGeO4:Bi3+,Eu3+ phosphor

We report on the design of ultraviolet (UV) emitting persistent (PersL) materials. Understanding the luminescence mechanism of Bi3+ ions, the occupation rules of sites, the density functional theory (DFT) calculations and an empirical energy level scheme guided us to select the most appropriate emitters, host and traps. Finally, the NaLuGeO4:Bi3+,Eu3+ phosphor was successfully designed. The experimental results indicated that the NaLuGeO4:Bi3+,Eu3+ material is indeed able to emit excellent UV PersL, which can be recorded for more than 63 h. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Accordingly, the excitation temperature-dependent and fading thermoluminescence experiments were conducted, and the trap properties were deeply studied by the initial rising method. The results reveal the PersL mechanism and the significant role of Eu3+ codopants as foreign traps. On the basis of this work, the UV PersL of the as-designed NaLuGeO4:Bi3+,Eu3+ material is certainly promising for some potential multifunctional applications, and the design concepts of this work are indeed effective and feasible for the design of PersL materials.

Host-sensitized white light-emitting phosphor MgY4Si3O13:Dy3+ with satisfactory thermal properties for UV-LEDs

A single-phase white-light emitting phosphor MgY4Si3O13:Dy3+ was synthesized using the solid state method under reducing atmosphere and in air for the first time. Upon ultraviolet light excitation, the phosphor exhibits intense warm white light emission with optimal CIE chromaticity coordinates of 0.432 and 0.421 and a correlated color temperature value of 3160 K. The emission intensities of samples synthesized under the reducing atmosphere are superior to those in air due to the sensitization of host to Dy3+. With the increase in temperature, MgY4Si3O13:Dy3+ presents satisfactory thermal properties and based on the configurational coordinate diagram, the energy transfer mechanism between the host and Dy3+ is carefully investigated. All the results indicate that MgY4Si3O13:Dy3+ could be a promising phosphor for warm white UV-LEDs.

Warm-white persistent luminescence of Lu3Al2Ga3O12:Pr3+ phosphor

Abstract A warm-white emitting persistent luminescence phosphor Lu 3 Al 2 Ga 3 O 12 :Pr 3+ was synthesized by solid state method at 1600 °C in air. The refined crystal structure of Lu 3 Al 2 Ga 3 O 12 host was solved by X-ray diffraction (XRD). The photoluminescence spectra, decay curve and thermoluminescence were investigated. It was revealed that the persistent luminescence originated from the f-f transitions of Pr 3+ emitters at Lu 3+ sites in LuO 8 polyhedrons, and it showed white color due to the 3 P 0 → 3 H 4 , 3 P 1 → 3 H 5 , 3 P 0 → 3 H 5 , 3 P 0 → 3 H 6 , 3 P 0 → 3 F 2 , 3 P 0 → 3 F 3 and 3 P 0 → 3 F 4 transitions of Pr 3+ emitters in a wide range. The persistent luminescence of Pr 3+ in this host could be promoted by f-d transition (278 nm) but f-f transitions, due to the different thermal activation energy. The persistent luminescence of the optimal sample could be actually recorded for 3 h by the definition of 0.32 mcd/m 2 and was visible for more than 7 h by dark-adapted vision in darkness. The initial depth of the dominant shallow traps was calculated to be about 0.56 eV, which is suitable for persistent luminescence. The different roles of the shallow and deep traps on the persistent decay process were investigated. Accordingly, the persistent luminescence processes and mechanism of the as-synthesized Lu 3 Al 2 Ga 3 O 12 :Pr 3+ phosphors were proposed.

Theoretical method to select appropriate codopants as efficient foreign electron traps for Lu 3 Al 2 Ga 3 O 12 :Tb 3+ /Ln 3+ persistent phosphor

Spectroscopic data in our investigation, combined with those in references, are used to construct an energy diagram of the typical Lu3Al2Ga3O12:Ln(2+)/Ln(3+) phosphors. Based on the diagram, the persistent luminescence properties of Lu3Al2Ga3O12:Ln(2+)/Ln(3+) (Ln = La-Yb) phosphors are theoretically predicted. We have shown that the position of the 4f ground level of Ln(2+) in the band gap can estimate the ability of Ln(3+) codopants as foreign electron traps, and it is confirmed by our experimental results of the typical Lu3Al2Ga3O12:Tb3+, Ln(3+) samples. Finally, the critical roles of the Yb3+ codopants as efficient foreign traps in the typical Lu3Al2Ga3O12:Tb3+ phosphor is revealed. The requirements for efficient foreign traps and the fundamental persistent luminescence mechanism of this phosphor are systematically summarized

A vivid example of turning waste into treasure: persistent luminescence of Ca2Ga2(Si,Ge)O7:Pr3+,Yb3+ phosphor tailored by band gap engineering

We exhibit a vivid example of turning waste into treasure for the development of persistent luminescence (PersL) phosphor. Facing the original experimental failure in which the as-synthesized Ca2Ga2SiO7:Pr3+,Yb3+ phosphor showed very weak PersL, we did not give up but made a deep analysis. It reveals that the relatively deep depth of traps (0.72 eV) may be the key reason for the weak PersL of Ca2Ga2SiO7:Pr3+,Yb3+ phosphor. Accordingly, in order to make the depth of the traps more shallow, a band gap engineering method was applied by the partial substitution of Si4+ with Ge4+ ions. Investigation into the optical spectra and the electronic structures indicate that the band gap has been successfully reduced. Correspondingly, the depth of traps becomes shallower, and it is adjusted in an appropriate range (around 0.65 eV) when Si : Ge = 1 : 9. As a consequence, the original “waste” phosphor with very weak PersL is successfully turned into a valuable PersL phosphor: Ca2Ga2(Si0.1Ge0.9)O7:Pr3+,Yb3+, whose PersL duration time and initial PersL brightness have been increased by 74 times and 52 times, respectively, compared with the original Ca2Ga2SiO7:Pr3+,Yb3+ sample.

Fabrication of hybrid Co 3 O 4 /NiCo 2 O 4 nanosheets sandwiched by nanoneedles for high-performance supercapacitors using a novel electrochemical ion exchange

Electrochemical ion exchange has been used to tailor the composition of transition metal oxides (Co3O4) electrode with enhanced capacity while maintaining its crystal structure and morphology. Specifically, Ni ions were incorporated to Co3O4 nanosheets sandwiched by nanoneedles to form Co3O4/NiCo2O4 composite. As positive electrode for supercapacitors, the Co3O4/NiCo2O4 composite presents a high areal capacitance of 3.2 F cm−2(1060 F g−1) at a current density of 5 mA cm−2 and outstanding rate capability as well as long cycle stability. Moreover, the assembled aqueous asymmetric supercapacitor based on Co3O4/NiCo2O4//carbon cloth electrodes delivers a considerable energy density of 3.0 mW h cm−3 at power density of 136 mW cm−3, and high rate capability (85% retention at a current density of 30 mA cm−2). A safety light composed of ten green LEDs in parallel was lit for ∼360 s using two identical supercapacitors in series, indicating a promising practical application.摘要离子交换技术被广泛用于调节过渡金属氧化物的成分, 采用该技术制备的超级电容器电极材料, 在保持其形貌的同时能增加其比容量. 本文报道了一种新颖的电化学方法辅助制备复合Co3O4/NiCo2O4纳米材料. 通过电化学离子交换, 可以将Ni2+快速引入并部分替换Co3O4纳米材料中的Co2+, 从而得到Co3O4和NiCo2O4的复合纳米材料.将其用作超级电容器正极材料, 在5 mA cm−2的电流密度下, 其面电容达到了3.2 F cm−2, 并展现出了良好的倍率性能及优异的循环稳定性. 此外, 两个串联的非对称器件(Co3O4/NiCo2O4//碳布)在充电3min后可以将10个并联的绿色LED点亮大约6 min, 展现出良好的实用性.

Nonequivalent Substitution and Charge-Induced Emitter-Migration Design of Tuning Spectral and Duration Properties of NaCa2GeO4F:Mn2+ Persistent Luminescent Phosphor

We combine nonequivalent substitution and charge-induced emitter-migration approaches and design an efficient method to optionally tune the spectral and duration properties of NaCa2GeO4F:Mn(2+) phosphor. A series of representative codopants have been investigated in detail and classified into two categories: RA (RA = Li(+), Al(3+), N(3-), Ga(3+), B(3+)) and RB (RB = Mg(2+), F(-), Bi(3+), Zn(2+), Cd(2+), Sc(3+), Tm(3+)). Results reveal that the nonequivalent substitution of RA codopants would induce foreign negative defects and stabilize Mn(2+) emitters at octahedral Na/Ca sites for red emission. In constrast, the RB codopants would generate foreign positive defects and make Mn(2+) emitters migrate to tetrahedral Ge(4+) sites for green-yellow emission. At the same time, the RA codopants are in favor of the generation of intrinsic positive traps with shallow trap depth and thus efficiently improve the duration properties of phosphors. On the basis of the experimental results, a possible nonequivalent substitution and charge-induced emitter-migration model has been proposed, and we can optionally tune the spectral (568 ↔ 627 nm) and the duration (minutes to more than 6 h) properties according to this model.