E. H. Song
South China University of Technology
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Featured researches published by E. H. Song.
Journal of Materials Chemistry C | 2017
T. T. Deng; E. H. Song; Jiayi Sun; Lei Wang; Y. Deng; S. Ye; Jian Wang; Q. Y. Zhang
Herein, a new red phosphor Na3GaF6:Mn4+ has been designed and synthesized by a facile two-step co-precipitation method at room temperature. Single crystal X-ray diffraction analysis reveals that the fluoride Na3GaF6 crystallizes in the P2(1)/n space group with a = 5.4760 A, b = 5.6862 A, c = 7.9009 A, β = 90.309°, and z = 2. Upon blue or UV light excitation, the obtained phosphor Na3GaF6:Mn4+ emits intense and pure red fluorescence. The effects of raw materials, doping concentration and environmental temperature on its luminescence properties and crystal structure have been investigated and discussed in detail. Such a newly synthesized red phosphor shows excellent anti-thermal quenching behavior (∼118.8% of emission intensity at 150 °C relative to 25 °C) and good color stability upon blue light (∼467 nm) excitation. By using the Na3GaF6:Mn4+ phosphor as a red light component, a high-power stable warm white light-emitting diode (WLED, Ra = 81, CCT = 2966 K, luminous efficacy = 56.73 lm W−1) was fabricated, further evidencing the potential of the as-synthesized Na3GaF6:Mn4+ phosphor for white LED applications.
Journal of Materials Chemistry C | 2016
E. H. Song; J. Q. Wang; S. Ye; Xiao-Fang Jiang; Mingying Peng; Q. Y. Zhang
A novel red fluoroaluminate phosphor, cryolite Na3AlF6:Mn4+, has been designed and synthesized via a facile two-step method at room temperature. Under blue light excitation, it exhibits intense sharp line red fluorescence (∼630 nm) with high color purity. The crystal structure, morphology and doping concentration of the samples were characterized in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ICP-AES. The influence of synthesis conditions, raw materials and doping concentration on crystal structure and photoluminescence (or decay behavior) has been investigated carefully. The optimal composition, Na3AlF6:1.58%Mn4+, shows a bright red light and excellent thermal stability (∼99.93% of the emission intensity at 200 °C relative to 23 °C) upon ∼467 nm blue light excitation. A warm high-power white LED with a high color rendering index (Ra = 92.7 and R9 = 94) and low color temperature (CCT = 3903 K) was fabricated based on the blue InGaN chip, commercial yellow phosphor YAG:Ce3+ and red phosphor Na3AlF6:Mn4+.
Journal of Materials Chemistry C | 2016
Ming Wu; E. H. Song; Zitao Chen; Siyang Ding; S. Ye; Jiajia Zhou; Shiqing Xu; Qinyuan Zhang
Single-band red upconversion (UC) emission of Er3+ has been successfully achieved in Yb3+/Er3+ codoped KMgF3 nanocrystals via a nonequivalent substitution strategy, in which lanthanide ions probably aggregate, as evidenced by density functional theory calculations and upconversion dynamic processes. The aggregation of Yb3+/Er3+ would cause large cross-relaxation probabilities among the lanthanide ions when photo-excited, resulting in the disappearance of the green emission and the population of the red emitting level of Er3+. Interestingly, the single-band feature is independent of the dopant concentration and pump power. The possible UC mechanism is discussed in detail according to nanocrystal morphology, ion radii, lattice parameters and decay lifetime studies of the Yb3+–Er3+ doped analogous compounds (KMgF3, KZnF3 and KCdF3). It could be concluded that Yb3+/Er3+ ions tend to aggregate in KMgF3, resulting in the largest ratio of red to green UC emission. This research may give a perspective toward tuning the UC emission of lanthanide ions.
ACS Applied Materials & Interfaces | 2016
Yuzhi Li; Linfeng Lan; Peng Xiao; Sheng Sun; Zhenguo Lin; Wei Song; E. H. Song; Peixiong Gao; Weijing Wu; Junbiao Peng
Short-channel electronic devices several micrometers in length are difficult to implement by direct inkjet printing due to the limitation of position accuracy of the common inkjet printer system and the spread of functional ink on substrates. In this report, metal oxide thin-film transistors (TFTs) with channel lengths of 3.5 ± 0.7 μm were successfully fabricated with a common inkjet printer without any photolithography steps. Hydrophobic CYTOP coffee stripes, made by inkjet-printing and plasma-treating processes, were utilized to define the channel area of TFTs with channel lengths as short as ∼3.5 μm by dewetting the inks of the source/drain (S/D) precursors. Furthermore, by introduction of an ultrathin layer of PVA to modify the S/D surfaces, the spreading of precursor ink of the InOx semiconductor layer was well-controlled. The inkjet-printed short-channel TFTs exhibited a maximum mobility of 4.9 cm(2) V(-1) s(-1) and an on/off ratio of larger than 10(9). This approach of fabricating short-channel TFTs by inkjet printing will promote the large-area fabrication of short-channel TFTs in a cost-effective manner.
Journal of Materials Chemistry C | 2017
Lei Wang; E. H. Song; Y. Y. Zhou; T. T. Deng; S. Ye; Q. Y. Zhang
Synthesis with low HF concentration or without HF is all along a fundamental challenge in the field of Mn4+-doped fluoride phosphors for warm-white light emitting diodes (WLEDs). We attempted here to synthesize a red emitting phosphor, Rb2ZrF6:Mn4+, through a two-step co-precipitation method by using H2O as a solvent instead of the highly toxic HF at room temperature. The structure, morphology and the formation mechanism as well as the effect of dopant concentration on the photoluminescence properties have been investigated systematically. The obtained Rb2ZrF6:Mn4+ phosphor shows intense blue absorption and presents satisfactory red emission with high color purity. The exploration of temperature-dependent luminescence reveals that the resultant sample exhibits preferable anti-thermal quenching behavior (∼103.3% of emission intensity at 120 °C relative to 20 °C) along with excellent color stability in the temperature range of 20–160 °C. Thereafter, the reliability examination in a HTHH (85 °C and 85% high humidity) environment indicates that Rb2ZrF6:Mn4+ exhibits favorable longevity. The device featuring the Rb2ZrF6:Mn4+ red phosphor displays good performance (CCT = 3569 K, Ra = 85.5, LE = 139.1 lm W−1), showing the great potential of the as-synthesized Rb2ZrF6:Mn4+ for indoor lighting applications.
Journal of Materials Chemistry C | 2017
T. T. Deng; E. H. Song; Y. Y. Zhou; Lei Wang; S. Ye; Q. Y. Zhang
A novel hydrous fluoride K2GaF5(H2O) with a special [GaF5(H2O)] group has been discovered. Interestingly, further rapidly adding K2MnF6 into the co-precipitation reaction system of K2GaF5(H2O) results in stable anhydrous cryolite phosphor K3GaF6:Mn4+. The investigation of a possible formation mechanism unravels that hydrous K2GaF5(H2O) can act as an intermediate to transform into anhydrous K3GaF6:Mn4+ induced by K2MnF6. Detailed characterizations, such as phase identification, morphology, elemental composition analysis, and IR spectra, record the time-dependent evolution process. Upon blue light excitation, phosphor K3GaF6:Mn4+ shows sharp line red emission at ∼626 nm. It presents good moisture tolerance (50% of initial luminous efficacy at 48 h), which might, due to the absence of coordinated water molecules, make the host matrix less hydrophilic. This performance, much better than those of Na3GaF6:Mn4+, K3AlF6:Mn4+, and Rb2GeF6:Mn4+, illustrates that K3GaF6 is a suitable host for Mn4+ doping. Besides, a good recovery in luminescence properties during thermal cycling (298–473 K) further demonstrates the high stability of anhydrous K3GaF6:Mn4+. By incorporating K3GaF6:Mn4+ as a red light component, a fabricated warm white light-emitting diode (WLED) presents low correlated color temperature (CCT = 3691 K), high color rendering index (Ra = 87.2 and R9 = 50.2), and a luminous efficacy of 92.1 lm W−1, and further exhibits good resistance in photoelectric properties to thermal impact with temperature ranging from 293 to 353 K, showing potential in warm WLED applications. Herein, the inductive transition from hydrous K2GaF5(H2O) to moisture-proof K3GaF6:Mn4+ is helpful for the investigation of the moisture resistance of Mn4+ activated fluorides. Moreover, these results probably propose a feasible strategy to exploit stable Mn4+-activated fluoride phosphors for warm WLED applications.
Journal of Materials Chemistry C | 2014
E. H. Song; Juanhong Wang; D. C. Yu; S. Ye; Q. Y. Zhang
In contrast to common visible emission, an anomalous near-infrared (NIR) emission band at 790 nm has been demonstrated in the spinel structure MgGa2O4:Mn2+ with heavy Mn2+ doping. Tunable single-band visible to visible-NIR and single-band NIR emission are easily realised upon tuning the doping concentration of Mn2+. Careful investigation of the crystal structure, fluorescence lifetime and excitation & emission spectra indicates that the NIR emission might be ascribed to the 6A1(6S)4T1(4G) → 6A1(6S)6A1(6S) transitions of Mn2+–Mn2+ dimers. When some Yb3+ ions are codoped into the spinel MgGa2O4:Mn2+, room temperature visible upconversion (UC) emission is realised upon excitation with a 976 nm laser diode. The temperature-dependent UC emission properties as well as the related UC mechanism have been investigated. Understanding the nature of the Mn2+ Stokes and UC emissions is the key to developing advanced photonic devices with improved properties and manufacturability for engineering applications.
Optical Materials Express | 2014
S. Ye; E. H. Song; E. Ma; S. J. Zhang; Jian Wang; Xianqiang Chen; Q. Y. Zhang; Jianrong Qiu
Broadband-light-sensitized upconversion (UC) photon management phenomenon in La3Ga5GeO14:Cr3+,Yb3+,Er3+ is reported, featuring the concentrated broadband noncoherent light excitable at room temperature. Energy transfer among Cr3+/Yb3+/Er3+ in the Stokes and UC luminescence processes reveals that Yb3+ as a “bridge” is requisite for Cr3+-sensitized UC luminescence of Er3+. Low Cr3+ contents are preferred for UC luminescence of Yb3+-Er3+, since it would be quenched by high Cr3+ contents. The designed UC emissions 2H11/2→4I15/2 and 4S3/2→4I15/2 of Er3+ at around 510 ~560 nm are proposed to through Energy transfer upconversion (ETU) mechanism based on the Cr3+-Yb3+ dimer model with superexchange interaction according to crystallographic data and the decay curves of Er3+ UC emission. This research may open up a new perspective to design novel photonic materials excitable by broadband noncoherent light for improving the photoresponse of solar cells.
Journal of Materials Chemistry C | 2017
T. T. Deng; E. H. Song; Y. Y. Zhou; Lei Wang; Q. Y. Zhang
Three isotypic double perovskites A2BAlF6:Mn4+ (A = Rb, Cs; B = K, Rb) were synthesized via a facile co-precipitation method at room temperature. XRD Rietveld refinements and Raman spectra indicate that the neighboring smaller A-site or larger B-site cation in A2BAlF6:Mn4+ lowers structural stability, but suppresses the [AlF6] octahedron to increase the crystal field strength and bond strength of the Al–F bond. Cs2KAlF6:Mn4+ presents a sharp line red light and excellent moisture resistance, but experiences severe thermal quenching. In comparison, altering the A- or B-site cation to Rb, Rb2KAlF6:Mn4+ and Cs2RbAlF6:Mn4+ shows blue shifts in emission and declining water resistance, but enhancements in thermal stability. A combination of static and dynamic emission degradations demonstrates that the water resistance of Mn4+ emission mainly relies on the structural stability of the host matrix; meanwhile, the thermal stability highly depends on the rigidity of its local accommodation. The variations of the temperature-dependent white light-emitting diode (WLED) performances further evidence their sufficient thermal stability for LED applications. These findings suggest that neighboring-cation modulation might be a feasible guideline for exploiting stable Mn4+-activated fluoride red phosphors in warm WLED applications.
Optical Materials Express | 2014
E. H. Song; Siyang Ding; Ming Wu; S. Ye; Zitao Chen; Yuguang Ma; Q. Y. Zhang
Tunable broadband white upconversion (UC) luminescence has been demonstrated in Yb3+/Tm3+/Mn2+ tri-doped KZnF3 nanocrystals from the excitation of a 976 nm laser diode (LD). The white light is composed of three sharp band peaks at 480, 650 and 700 nm, originating from the UC emissions of Tm3+ ions, and one broad band centered at 585 nm, originating from exchange-coupled Yb3+–Mn2+ dimers. The effects of the concentration, pump power and temperature on the UC luminescence properties of KZnF3:Yb3+,Tm3+,Mn2+ nanocrystals have been investigated. By changing the Mn2+/Tm3+ content ratio, various colors of the UC luminescence can be easily obtained in KZnF3:Yb3+,Tm3+,Mn2+ nanocrystals, which gives these nanocrystals potential applications in the fields of lighting, displays and lasers.