16 research outputs found
Data_Sheet_1_Biocontrol efficacy of Bacillus velezensis strain YS-AT-DS1 against the root-knot nematode Meloidogyne incognita in tomato plants.docx
Root-knot nematodes (RKNs; Meloidogyne spp.), one of the most economically important plant-parasitic nematodes (PPNs), cause severe yield and quality losses in agriculture annually. The application of biological control agents is an environmentally safe and effective approach to control RKNs. Here, we report the genomic characteristics of a Bacillus velezensis strain YS-AT-DS1 (Bv-DS1) isolated from the tidal soil, revealing that it has a 4.73 Mb circular chromosome with an average GC-content of 46.43%, 3,977 genes, 86 tRNAs, and 27 rRNAs, and contains secondary metabolite clusters for producing antimicrobial compounds. In vitro assays indicated that Bv-DS1 has not only antagonistic activities against fungal pathogens, but also shows nematicidal activity, with a mortality rate of 71.62% mortality rates in second-stage juvenile (J2s) Meloidogyne incognita. We then focused on the biocontrol efficiency of Bv-DS1 against M. incognita in pot assays. Preinoculation with Bv-DS1 enhanced tomato growth, and significantly reduced the infection rate of J2s, and the number of galls and egg masses on tomato roots. The underlying mechanism in Bv-DS1-induced resistance to M. incognita was further investigated through split-root experiments, and analysing the expression of the genes related to jasmonic acid (JA), salicylic acid (SA), and the tonoplast intrinsic protein (TIP). The results indicated that Bv-DS1 could not activate host systemic-induced resistance (ISR) in the split-root system of tomatoes. Additionally, the expression of JA- (LOX D and MC) and SA- (PAL2 and PR) responsive genes did not change in Bv-DS1-pretreated plants at 3 and 14 days after nematode inoculation. The presented data showed that JA-and SA-dependent pathways were not required for the biocontrol action of the Bv-DS1 against RKN. The TIP genes, responsible for transport of water and small substrates in plants, have previously been shown to negatively regulate the parasitism of PPNs. Surprisingly, Bv-DS1 compromised the downregulation of TIP1.1 and TIP1.3 by M. incognita. Together, our data suggest that Bv-DS1 exhibits a dual effect on plant growth promotion and protection against RKN, possibly related to the regulation of water and solute transport via TIPs. Thus, the Bv-DS1 strain could be used as a biocontrol agent for RKN control in sustainable agriculture.</p
Highly Thermally Stable Single-Component White-Emitting Silicate Glass for Organic-Resin-Free White-Light-Emitting Diodes
Thermal management is still a great challenge for high-power phosphor-converted white-light-emitting diodes (pc-WLEDs) intended for future general lighting. In this paper, a series of single-component white-emitting silicate SiO<sub>2</sub>–Li<sub>2</sub>O–SrO–Al<sub>2</sub>O<sub>3</sub>–K<sub>2</sub>O–P<sub>2</sub>O<sub>5</sub>: Ce<sup>3+</sup>, Tb<sup>3+</sup>, Mn<sup>2+</sup> (SLSAKP: Ce<sup>3+</sup>, Tb<sup>3+</sup>, Mn<sup>2+</sup>) glasses that simultaneously play key roles as a luminescent convertor and an encapsulating material for WLEDs were prepared via the conventional melt-quenching method, and systematically studied using their absorption spectra, transmittance spectra, photoluminescence excitation and emission spectra in the temperature range 296–498 K, decay curves, and quantum efficiency. The glasses show strong and broad absorption in 250–380 nm region and exhibit intense white emission, produced by in situ mixing of blue-violet, green, and orange-red light from Ce<sup>3+</sup>, Tb<sup>3+</sup>, and Mn<sup>2+</sup> ions, respectively, in a single glass component. The quantum efficiency of SLSAKP: 0.3%Ce<sup>3+</sup>, 2.0%Tb<sup>3+</sup>, 2.0%Mn<sup>2+</sup> glass is determined to be 19%. More importantly, this glass shows good thermal stability, exhibiting at 373 and 423 K about 84.56 and 71.02%, respectively, of the observed room temperature (298 K) emission intensity. The chromaticity shift of SLSAKP: 0.3%Ce<sup>3+</sup>, 2.0%Tb<sup>3+</sup>, 2.0%Mn<sup>2+</sup> is 2.94 × 10<sup>–2</sup> at 498 K, only 57% of the commercial triple-color white-emitting phosphor mixture. Additionally, this glass shows no transmittance loss at the 370 nm emission of a UV-Chip-On-Board (UV-COB) after thermal aging for 240 h, compared with the 82% transmittance loss of epoxy resin. The thermal conductivity of the glass is about 1.07 W/mK, much larger than the 0.17 W/mK of epoxy resin. An organic-resin-free WLEDs device based on SLSAKP: 0.3%Ce<sup>3+</sup>, 2.0%Tb<sup>3+</sup>, 2.0%Mn<sup>2+</sup> glass and UV-COB is successfully demonstrated. All of our results demonstrate that the presented Ce<sup>3+</sup>/Tb<sup>3+</sup>/Mn<sup>2+</sup> tridoped lithium–strontium–silicate glass may serve as a promising candidate for high-power WLEDs
Site Occupancies, Luminescence, and Thermometric Properties of LiY<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub>:Ce<sup>3+</sup> Phosphors
In this work, we
report the tunable emission properties of Ce<sup>3+</sup> in an apatite-type
LiY<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub> compound
via adjusting the doping concentration or temperature. The occupancies
of Ce<sup>3+</sup> ions at two different sites (Wyckoff 6h and 4f
sites) in LiY<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub> have been determined by Rietveld refinements. Two kinds of Ce<sup>3+</sup> f–d transitions have been studied in detail and then
assigned to certain sites. The effects of temperature and doping concentration
on Ce<sup>3+</sup> luminescence properties have been systematically
investigated. It is found that the Ce<sup>3+</sup> ions prefer occupying
Wyckoff 6h sites and the energy transfer between Ce<sup>3+</sup> at
two sites becomes more efficient with an increase in doping concentration.
In addition, the charge-transfer vibronic exciton (CTVE) induced by
the existence of free oxygen ion plays an important role in the thermal
quenching of Ce<sup>3+</sup> at 6h sites. Because of the tunable emissions
from cyan to blue with increasing temperature, the phosphors LiY<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub>:Ce<sup>3+</sup> are endowed with possible thermometric applications
Defect Structure, Phase Separation, and Electrical Properties of Nonstoichiometric Tetragonal Tungsten Bronze Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub>
New
insight into the defect chemistry of the tetragonal tungsten bronze
(TTB) Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub> is established here, which is shown to adapt to
a continuous and extensive range of both cationic and anionic defect
stoichiometries. The highly nonstoichiometric TTB Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub> (<i>x</i> = 0.25–0.325) compositions are stabilized via the
interpolation of Ba<sup>2+</sup> cations and (TaO)<sup>3+</sup> groups
into pentagonal tunnels, forming distinct Ba chains and alternate
Ta-O rows in the pentagonal tunnels along the <i>c</i> axis.
The slightly nonstoichiometric Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub> (<i>x</i> = 0–0.1) compositions incorporate framework oxygen and tunnel
cation deficiencies in the TTB structure. These two mechanisms result
in phase separation within the 0.1< <i>x</i> < 0.25
nonstoichiometric range, resulting in two closely related (TaO)<sup>3+</sup>-containing and (TaO)<sup>3+</sup>-free TTB phases. The highly
nonstoichiometric (TaO)<sup>3+</sup>-containing phase exhibits Ba<sup>2+</sup> cationic migration. The incorporation of (TaO)<sup>3+</sup> units into the pentagonal tunnel and the local relaxation of the
octahedral framework around the (TaO)<sup>3+</sup> units are revealed
by diffraction data analysis and are shown to affect the transport
and polarization properties of these compositions
Defect Structure, Phase Separation, and Electrical Properties of Nonstoichiometric Tetragonal Tungsten Bronze Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub>
New
insight into the defect chemistry of the tetragonal tungsten bronze
(TTB) Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub> is established here, which is shown to adapt to
a continuous and extensive range of both cationic and anionic defect
stoichiometries. The highly nonstoichiometric TTB Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub> (<i>x</i> = 0.25–0.325) compositions are stabilized via the
interpolation of Ba<sup>2+</sup> cations and (TaO)<sup>3+</sup> groups
into pentagonal tunnels, forming distinct Ba chains and alternate
Ta-O rows in the pentagonal tunnels along the <i>c</i> axis.
The slightly nonstoichiometric Ba<sub>0.5–<i>x</i></sub>TaO<sub>3–<i>x</i></sub> (<i>x</i> = 0–0.1) compositions incorporate framework oxygen and tunnel
cation deficiencies in the TTB structure. These two mechanisms result
in phase separation within the 0.1< <i>x</i> < 0.25
nonstoichiometric range, resulting in two closely related (TaO)<sup>3+</sup>-containing and (TaO)<sup>3+</sup>-free TTB phases. The highly
nonstoichiometric (TaO)<sup>3+</sup>-containing phase exhibits Ba<sup>2+</sup> cationic migration. The incorporation of (TaO)<sup>3+</sup> units into the pentagonal tunnel and the local relaxation of the
octahedral framework around the (TaO)<sup>3+</sup> units are revealed
by diffraction data analysis and are shown to affect the transport
and polarization properties of these compositions
Combined Experimental and ab Initio Study of Site Preference of Ce<sup>3+</sup> in SrAl<sub>2</sub>O<sub>4</sub>
Low-temperature
photoluminescence properties of Sr<sub>1–2<i>x</i></sub>Ce<sub><i>x</i></sub>Na<sub><i>x</i></sub>Al<sub>2</sub>O<sub>4</sub> (<i>x</i> = 0.001) synthesized
by a solid-state reaction method are measured with excitation energies
in the vacuum ultraviolet (VUV) to ultraviolet (UV) range. Two distinct
activator centers with different emission and excitation intensities
are observed and attributed to Ce<sup>3+</sup> occupying the Sr1 and
Sr2 sites of SrAl<sub>2</sub>O<sub>4</sub> with different probabilities.
Hybrid density functional theory (DFT) calculations within the supercell
model are then carried out to optimize the local structures of Ce<sup>3+</sup> located at the two Sr sites of SrAl<sub>2</sub>O<sub>4</sub>, on which wave function-based CASSCF/CASPT2 embedded cluster calculations
with the spin–orbit effect are performed to derive the Ce<sup>3+</sup> 4f<sup>1</sup> and 5d<sup>1</sup> energy levels. On the
basis of the observed relative spectral intensities, the calculated
DFT total energies, and the comparison between experimental and calculated
4f → 5d transition energies, we conclude that, in SrAl<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup>, the dopant Ce<sup>3+</sup> prefers
to occupy the slightly smaller Sr2 site, rather than the larger Sr1
site as proposed earlier. Furthermore, by using an established linear
relationship between the lowest 4f → 5d transition energies
of Ce<sup>3+</sup> and Eu<sup>2+</sup> located at the same site of
a given compound, we find that, in SrAl<sub>2</sub>O<sub>4</sub>:Eu<sup>2+</sup>, the dominant green emission observed at room temperature
arises from Eu<sup>2+</sup> located at the Sr2 site of SrAl<sub>2</sub>O<sub>4</sub>
Tunable Luminescent Properties and Concentration-Dependent, Site-Preferable Distribution of Eu<sup>2+</sup> Ions in Silicate Glass for White LEDs Applications
The design of luminescent materials
with widely and continuously tunable excitation and emission is still
a challenge in the field of advanced optical applications. In this
paper, we reported a Eu<sup>2+</sup>-doped SiO<sub>2</sub>-Li<sub>2</sub>O-SrO-Al<sub>2</sub>O<sub>3</sub>-K<sub>2</sub>O-P<sub>2</sub>O<sub>5</sub> (abbreviated as SLSAKP:Eu<sup>2+</sup>) silicate luminescent
glass. Interestingly, it can give an intense tunable emission from
cyan (474 nm) to yellowish-green (538 nm) simply by changing excitation
wavelength and adjusting the concentration of Eu<sup>2+</sup> ions.
The absorption spectra, photoluminescence excitation (PLE) and emission
(PL) spectra, and decay curves reveal that there are rich and distinguishable
local cation sites in SLSAKP glasses and that Eu<sup>2+</sup> ions
show preferable site distribution at different concentrations, which
offer the possibility to engineer the local site environment available
for Eu<sup>2+</sup> ions. Luminescent glasses based color and white
LED devices were successfully fabricated by combining the as-synthesized
glass and a 385 nm n-UV LED or 450 nm blue LED chip, which demonstrates
the potential application of the site engineering of luminescent glasses
in advanced solid-state lighting in the future
Site-Dependent Luminescence and Thermal Stability of Eu<sup>2+</sup> Doped Fluorophosphate toward White LEDs for Plant Growth
Eu<sup>2+</sup> activated fluorophosphate
Ba<sub>3</sub>GdNa(PO<sub>4</sub>)<sub>3</sub>F (BGNPF) with blue
and red double-color emitting samples were prepared via a solid-state
method in a reductive atmosphere. Their crystal structure and cationic
sites were identified in light of X-ray diffraction pattern Rietveld
refinement. Three different Ba<sup>2+</sup> sites, coordinated by
six O atoms referred to as Ba1, two F and five O atoms as Ba2, and
two F and six O atoms as Ba3, were partially substituted by Eu<sup>2+</sup>. Photoluminescence emission (PL) and excitation (PLE) spectra
of phosphor BGNPF:Eu<sup>2+</sup> along with the lifetimes were characterized
at the liquid helium temperature (LHT), which further confirm the
existence of three Eu<sup>2+</sup> emitting centers resulting in 436,
480, and 640 nm emission from the 5d → 4f transitions of Eu<sup>2+</sup> in three different Ba<sup>2+</sup> crystallographic sites.
These emissions overlap with the absorption spectra of carotenoids
and chlorophylls from plants, which could directly promote the photosynthesis.
Temperature-dependent PL spectra were used to investigate the thermal
stability of phosphor, which indicates that the PL intensity of BGNPF:0.9%
Eu<sup>2+</sup> with optimal composition at 150 °C still keeps
60% of its PL intensity at room temperature, in which blue emission
has higher thermal-stability than the red emission. Furthermore, the
approaching white LED devices have also been manufactured with a 365
nm n-UV LED chip and present phosphor, which make operators more comfortable
than that of the plant growth purple emitting LEDs system composed
of blue and red light. Results indicate that this phosphor is an attractive
dual-responsive candidate phosphor in the application n-UV light-excited
white LEDs for plant growth
Excitation Wavelength Dependent Luminescence of LuNbO<sub>4</sub>:Pr<sup>3+</sup>Influences of Intervalence Charge Transfer and Host Sensitization
A series
of LuNbO<sub>4</sub>:Pr<sup>3+</sup> phosphors was prepared
by a solid-state reaction method at high-temperature. Rietveld refinements
were performed based on powder X-ray diffraction (XRD) data. Diffuse
reflectance spectra (DRS), UV–vis photoluminescence (PL), time-resolved
emission spectra (TRES), and fluorescence decays were utilized to
study the luminescence and host sensitization processes of Pr<sup>3+</sup> in LuNbO<sub>4</sub>. Excitation wavelength dependent luminescence
of LuNbO<sub>4</sub>:Pr<sup>3+</sup> was investigated and explained
in consideration of the processes of nonradiation relaxation via cross-relaxation,
multiphonon relaxation, and crossover to the intervalence charge transfer
(IVCT) state. Furthermore, the host sensitization of Pr<sup>3+</sup> emission in LuNbO<sub>4</sub> was confirmed and the energy transfer
efficiency from host to Pr<sup>3+</sup> increased with increasing
Pr<sup>3+</sup> doping concentration/temperature. Because the change
of emission intensities for both blue from the host and red from <sup>1</sup>D<sub>2</sub> is sensitive to temperature, a large variation
of emission color is observed between RT and 500 K
Localization of Oxygen Interstitials in CeSrGa<sub>3</sub>O<sub>7+δ</sub> Melilite
The
solubility of Ce in the La<sub>1–<i>x</i></sub>Ce<sub><i>x</i></sub>SrGa<sub>3</sub>O<sub>7+δ</sub> and
La<sub>1.54–<i>x</i></sub>Ce<sub><i>x</i></sub>Sr<sub>0.46</sub>Ga<sub>3</sub>O<sub>7.27+δ</sub> melilites
was investigated, along with the thermal redox stability in air of
these melilites and the conductivity variation associated with oxidization
of Ce<sup>3+</sup> into Ce<sup>4+</sup>. Under CO reducing atmosphere,
the La in LaSrGa<sub>3</sub>O<sub>7</sub> may be completely substituted
by Ce to form the La<sub>1–<i>x</i></sub>Ce<sub><i>x</i></sub>SrGa<sub>3</sub>O<sub>7+δ</sub> solid solution,
which is stable in air to ∼600 °C when <i>x</i> ≥ 0.6. On the other side, the La<sub>1.54–<i>x</i></sub>Ce<sub><i>x</i></sub>Sr<sub>0.46</sub>Ga<sub>3</sub>O<sub>7.27+δ</sub> compositions displayed much lower
Ce solubility (<i>x</i> ≤ 0.1), irrespective of the
synthesis atmosphere. In the as-made La<sub>1–<i>x</i></sub>Ce<sub><i>x</i></sub>SrGa<sub>3</sub>O<sub>7+δ</sub>, the conductivity increased with the cerium content, due to the
enhanced electronic conduction arising from the 4f electrons in Ce<sup>3+</sup> cations. At 600 °C, CeSrGa<sub>3</sub>O<sub>7+δ</sub> showed a conductivity of ∼10<sup>–4</sup> S/cm in
air, nearly 4 orders of magnitude higher than that of LaSrGa<sub>3</sub>O<sub>7</sub>. The oxidation of Ce<sup>3+</sup> into Ce<sup>4+</sup> in CeSrGa<sub>3</sub>O<sub>7+δ</sub> slightly reduced the
conductivity, and the oxygen excess did not result in apparent increase
of oxide ion conduction in CeSrGa<sub>3</sub>O<sub>7+δ</sub>. The Ce doping in air also reduced the interstitial oxide ion conductivity
of La<sub>1.54</sub>Sr<sub>0.46</sub>Ga<sub>3</sub>O<sub>7.27</sub>. Neutron powder diffraction study on CeSrGa<sub>3</sub>O<sub>7.39</sub> composition revealed that the extra oxygen is incorporated in the
four-linked GaO<sub>4</sub> polyhedral environment, leading to distorted
GaO<sub>5</sub> trigonal bipyramid. The stabilization and low mobility
of interstitial oxygen atoms in CeSrGa<sub>3</sub>O<sub>7+δ</sub>, in contrast with those in La<sub>1+<i>x</i></sub>Sr<sub>1–<i>x</i></sub>Ga<sub>3</sub>O<sub>7+0.5<i>x</i></sub>, may be correlated with the cationic size contraction
from the oxidation of Ce<sup>3+</sup> to Ce<sup>4+</sup>. These results
provide a new comprehensive understanding of the accommodation and
conduction mechanism of the oxygen interstitials in the melilite structure