Significantly enhanced photoluminescence and thermal stability of La3Si8N11O4:Ce3+,Tb3+via the Ce3+ → Tb3+ energy transfer: a blue-green phosphor for ultraviolet LEDs

A series of Ce³⁺-, Tb³⁺- and Ce³⁺/Tb³⁺-doped La₃Si₈N₁₁O₄ phosphors were synthesized by gas-pressure sintering (GPS). The energy transfer between Ce³⁺ and Tb³⁺ occurred in the co-doped samples, leading to a tunable emission color from blue to green under the 360 nm excitation. The energy transfer mechanism was controlled by the dipole–dipole interaction. The Ce³⁺/Tb³⁺ co-doped sample had an external quantum efficiency of 46.7%, about 5.6 times higher than the Tb-doped La₃Si₈N₁₁O₄ phosphor (8.3%). The thermal quenching of the Tb³⁺ emission in La₃Si₈N₁₁O₄:Tb,Ce was greatly reduced from 74 to 30% at 250 °C, owing to the energy transfer from Ce³⁺ to Tb³⁺. The blue-green La₃Si₈N₁₁O₄:0.01Ce,0.05Tb phosphor was testified to fabricate a warm white LED that showed a high color rendering index of 90.2 and a correlated color temperature of 3570 K. The results suggested that the co-doped La₃Si₈N₁₁O₄:Ce,Tb phosphor could be a potential blue-green down-conversion luminescent material for use in UV-LED pumped wLEDs.

The peak emission intensity and thermal stability of Tb³⁺ in codoped La₃Si₈N₁₁O₄:Ce,Tb sample are strongly enhanced via Ce³⁺ to Tb³⁺ energy transfer.     

Development of a cyan blue-emitting Ba3La2(BO3)4:Ce3+,Tb3+ phosphor for use in dental glazing materials: color tunable emission and energy transfer

The Ce³⁺/Tb³⁺ doped Ba₃La₂(BO₃)₄ phosphors were synthesized by a conventional solid state reaction method. The synthesized phosphor samples are a single phase of Ba₃La₂(BO₃)₄ and showed angular-shaped fine grains with average particle size from 5 μm to 10 μm. The Ba₃La₂(BO₃)₄:Ce³⁺ phosphors showed an asymmetric broad blue emission under excitation at 365 nm and the Ba₃La₂(BO₃)₄:Tb³⁺ phosphors exhibited typical green emission assigned to the 4f–4f transition of Tb³⁺ under excitation at 254 nm. Under near-UV (365 nm) excitation, Ba₃La₂(BO₃)₄:Ce³⁺,Tb³⁺ phosphors showed both a blue emission band and green emission peaks due to Ce³⁺ and Tb³⁺, respectively. By optimizing the composition, cyan-blue emission with high color purity (CIE chromaticity coordinate values x = 0.2557 and y = 0.3839) was obtained for the Ba₃La₂(BO₃)₄:0.05Ce³⁺,0.03Tb³⁺ phosphor, and the internal quantum efficiency of the phosphor at the excitation wavelength of 365 nm is estimated to be 50%. The dental glazing paste prepared by mixing organic binder, Ba₃La₂(BO₃)₄:Ce³⁺,Tb³⁺ phosphors, and low T_g glass was successfully vitrified when it was heated at 600 and 700 °C, and showed high chemical stability of the luminescence properties in acidic aqueous solution (pH = 4).

Herein, we demonstrated the possibility of using Ba₃La₂(BO₃)₄:Ce³⁺,Tb³⁺ phosphors in dental glazing paste.     

Pressure-induced phase transition of La2Zr2O7 and La0.5Gd1.5Zr2O7 pyrochlore

In situ high-pressure experiments on La₂Zr₂O₇ and La_0.5Gd_1.5Zr₂O₇ have been carried out at up to approximately 40 GPa using synchrotron X-ray diffraction and Raman spectroscopy combined with a diamond anvil cell technique. Both La₂Zr₂O₇ and La_0.5Gd_1.5Zr₂O₇ undergo a phase transition from a pyrochlore phase (Fd$\bar{3}$m) into a cotunnite-like phase (Pnma) at 22.7 and 23.3 GPa, respectively. This type of phase transition is mainly controlled through the order-disorder occupancy of cations, and Gd³⁺ substitution of La³⁺ reduces the stability of zirconate pyrochlore. However, abnormal changes to the unit-cell volumes and vibrational modes observed at 5.5 GPa in La₂Zr₂O₇ and 6.5 GPa in La_0.5Gd_1.5Zr₂O₇ are attributed to an anion disorder in the pyrochlore.

In situ high-pressure experiments on La₂Zr₂O₇ and La_0.5Gd_1.5Zr₂O₇ have been carried out at up to approximately 40 GPa using synchrotron X-ray diffraction and Raman spectroscopy combined with a diamond anvil cell technique.     

Effect of Bi3+ ion on upconversion-based induced optical heating and temperature sensing characteristics in the Er3+/Yb3+ co-doped La2O3 nano-phosphor

The upconversion-based optical heating and temperature sensing characteristics are investigated in the Er³⁺/Yb³⁺/Bi³⁺ tri-doped La₂O₃ nano-phosphor synthesized through a solution combustion method. The structural measurements reveal an increase in lattice parameters and particles size of the phosphor on increasing the concentrations of Bi³⁺ ions. The energy dispersive spectroscopic (EDS) measurements confirm the presence of La, Er, Yb, Bi and O elements in the tri-doped phosphor. The absorption spectra show the large number of bands due to Er³⁺, Yb³⁺ and Bi³⁺ ions. The Er³⁺/Yb³⁺ co-doped phosphor gives strong green emission bands at 523 and 548 nm upon 976 nm excitation due to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ ion, respectively. The emission intensity of these bands is enhanced upto 15 times in the presence of Bi³⁺ ions. The emission intensities of the 523 and 548 nm bands vary non-linearly with the pump power. The fluorescence intensity ratio (FIR) of the thermally coupled 523 and 548 nm emission bands shows efficient optical heating in the tri-doped phosphor. The FIR of the 523 and 548 nm emission bands further varies with the increase in temperature of the phosphor. The relative temperature sensing sensitivity has been calculated to be 71 × 10⁻⁴ K⁻¹ at 450 K for the tri-doped phosphor. Thus, the Er³⁺/Yb³⁺/Bi³⁺ tri-doped La₂O₃ nano-phosphor may provide a platform to use it in the photonic devices, as an optical heater and temperature sensor.

The Er³⁺/Yb³⁺/Bi³⁺ tri-doped La₂O₃ nano-phosphor gives efficient induced optical heating and temperature sensing. This study is useful to understand these characteristics in different materials with various pump powers and temperatures.     

The geometrical structure and electronic properties of trivalent Ho3+ doped Y2O3 crystals: a first-principles study

Trivalent rare-earth holmium ion (Ho³⁺) doped yttrium oxide (Y₂O₃) has attracted great research interest owing to its unique optoelectronic properties and excellent performances in many new-type laser devices. But the crystal structures of the Ho³⁺-doped Y₂O₃ system (Y₂O₃ : Ho) are still unclear. Here, we have carried out a first-principle study on the structural evolution of the trivalent Ho³⁺ doped Y₂O₃ by using the CALYPSO structure search method. The results indicate that the lowest-energy structure of Ho³⁺-doped Y₂O₃ possesses a standardized monoclinic P2 phase. It is found that the doped Ho³⁺ ion are likely to occupy the sites of Y³⁺ in the host crystal lattice, forming the [HoO₆]⁹⁻ local structure with C₂ site symmetry. Electronic structure calculations reveal that the band gap value of Ho³⁺-doped Y₂O₃ is approximately 4.27 eV, suggesting the insulating character of Y₂O₃ : Ho system. These findings could provide fundamental insights to understand the atomic interactions in crystals as well as the information of electronic properties for other rare-earth-doped materials.

Our study successfully identified the ground-state structure of Ho³⁺-doped Y₂O₃ crystal for the first time.     

Synthesis and characterization of a ZnGa2O4:Cr3+-based aerogel

A ZnGa₂O₄:Cr³⁺-based aerogel was prepared by using polyacrylic acid (PAA) as a dispersant and propylene oxide (PO) as a crosslinking agent via CO₂ supercritical drying. The results of BET and SEM show that there is a certain degree of macroporosity (d > 50 nm) in the aerogel. It has a dendritic structure and the interior is relatively loose. EDS mapping illustrates that the elements Zn, Ga, and Cr are evenly distributed in the aerogel. In addition, the diffuse reflectance spectra and the emission spectrum of samples with different calcination temperatures were also characterized. Both demonstrated, when the calcination temperature is greater than 600 °C, that the sample crystallizes and has a significant emission, which is consistent with the XRD and TG-DSG results. Finally, the ZnGa₂O₄:Cr³⁺-based aerogel also exhibits excellent long afterglow performance and high photocatalytic performance with 80.1% methylene blue (MB) degradation at 20 min.

A ZnGa₂O₄:Cr³⁺-based aerogel was prepared by using polyacrylic acid (PAA) as a dispersant and propylene oxide (PO) as a crosslinking agent via CO₂ supercritical drying.     

Impact of rare earth (RE3+ = La3+, Sm3+) substitution in the A site perovskite on the structural,and electrical properties of Ba(Zr0.9Ti0.1)O3 ceramics

Undoped Ba(Zr_0.9Ti_0.1)O₃ and rare-earth-doped (Ba_1−xRE_2x/3)(Zr_0.9Ti_0.1)O₃ (RE³⁺ = La³⁺, Sm³⁺) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr_0.9Ti_0.1)O₃ and formation of perovskite structure with the Pm$\bar{3}$m space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure–electrical property relationships.

Undoped Ba(Zr_0.9Ti_0.1)O₃ and rare-earth-doped (Ba_1−xRE_2x/3)(Zr_0.9Ti_0.1)O₃ (RE³⁺ = La³⁺, Sm³⁺) perovskite compounds were synthesized by the conventional solid-state reaction route.     

Up-conversion white emission and other luminescence properties of a YAG:Yb2O3·Tm2O3·Ho2O3@SiO2 glass-nanocomposite

We report on a glass-nanocomposite material consisting of yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) nanocrystals co-doped with Yb³⁺, Tm³⁺ and Ho³⁺ ions as well as entrapped into a SiO₂ xerogel. This 94YAG·5Yb₂O₃·0.8Tm₂O₃·0.2Ho₂O₃@SiO₂ (abbr. YAG:YbTmHo@SiO₂) nanocomposite material has been prepared by sol–gel procedure. Its structure and morphology has been characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques as well as energy dispersive X-ray (EDX), X-ray photoelectron (XPS) and luminescence spectroscopies. The luminescent glass-nanocomposite exhibited an up-conversion effect under λ_exc = 980 nm and emission when excited under 355 nm in steady-state conditions. Then time-resolved luminescence emission was observed, when the sample was excited at 290 and 355 nm by a pulse laser. Average decay times for the SiO₂ matrix and for some transitions of the Tm³⁺ and Ho³⁺ dopants present in the YAG:YbTmHo@SiO₂ material have been evaluated. The luminescent nanocomposite when excited under 290 or 355 nm wavelengths in both conditions emits blue light. However, the nanocomposite is promising as a single-source white-light phosphor owing to its up-conversion luminescence under 980 nm excitation. Such optical features make the studied material an alternative phosphor.

We present a glass-nanocomposite of the type YAG:YB³⁺, Tm³⁺, Ho³⁺@SiO₂ as an alternative white phosphor based on up-conversion effect.     

Luminescence properties and energy transfer of the near-infrared phosphor Ca3In2Ge3O12:Cr3+,Nd3+

The double doping strategy based on energy transfer is an effective way to regulate the NIR spectral distribution. In this work, Ca₃In₂Ge₃O₁₂:xNd³⁺ (CIG:xNd³⁺) and Ca_3−xIn_1.93Ge₃O₁₂:0.07Cr³⁺,yNd³⁺ (CIG:0.07Cr³⁺,yNd³⁺) phosphors are successfully prepared via a high-temperature solid-state method. CIG:0.07Cr³⁺ shows broadband emission centered at 804 nm, which covers most of the excitation peaks of Nd³⁺ ions. Under excitation at 480 nm, Cr³⁺ can provide effective energy transfer to Nd³⁺. In addition, CIG:0.07Cr³⁺,0.15Nd³⁺ has good temperature stability, and maintains 68.98% of the room-temperature intensity at 150 °C. The phosphors can convert short-wave photons to long-wave photons and enhance solar cell utilization, demonstrating the potential application of this material in solar spectral conversion technology.

Improvement of the luminescence properties of Ca₃In₂Ge₃O₁₂:Cr³⁺,Nd³⁺via energy transfer and its potential application in silicon solar cells.     

Luminescence and energy transfer of warm white-emitting phosphor Mg2Y2Al2Si2O12:Dy3+,Eu3+ for white LEDs

A series of Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ phosphors were synthesized by the solid-state method. The luminescent properties and crystal structures of the Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ phosphors were analyzed. The XRD results show that the synthesized Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ phosphors are of pure phase. Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺ can emit blue and yellow light under 367 nm light excitation; when doped with Eu³⁺, there is an obvious energy transfer from Dy³⁺ to Eu³⁺, and warm white light can be realized by adjusting the concentrations of Dy³⁺ and Eu³⁺ in Mg₂Y₂Al₂Si₂O₁₂. A warm white LED device was fabricated by combining Mg₂Y_1.88Al₂Si₂O₁₂:0.05Dy³⁺,0.07Eu³⁺ and a UV LED chip (370 nm) under a voltage of 3.2 V and current of 5 mA, the characteristics of the white LED being CIE = (0.4071, 0.3944), CCT = 3500 K and CRI = 91.3.

MYAS:xDy³⁺,yEu³⁺ can produce warm white light with CIE chromaticity coordinates of (0.4071, 0.3944) and relative color temperature of 3500 K.     

Impact of Cu doping on the structural,morphological and optical activity of V2O5 nanorods for photodiode fabrication and their characteristics

In this paper, we report a wet chemical precipitation method used to synthesize pure and Cu-doped V₂O₅ nanorods with different doping concentrations (Cu_xV₂O₅ where x = 3, 5 or 7 at%), followed by annealing at 600 °C and characterizations using several techniques. Indeed, a growth mechanism explaining the morphological evolution under the experimental conditions is also proposed. The XRD patterns revealed that all of the studied samples consist of a single V₂O₅ phase and are well crystallized with a preferential orientation towards the (200) direction. The presence of intrinsic defects and internal stresses in the lattice structure of the Cu_xV₂O₅ samples has been substantiated by detailed analysis of the XRD. Apart from the doping level, there was an assessment of identical tiny peaks attributed to the formation of a secondary phase of CuO. SEM images confirmed the presence of agglomerated particles on the surface; the coverage increased with Cu doping level. XPS spectral analysis showed that Cu in the V⁵⁺ matrix exists mainly in the Cu²⁺ state on the surface. The appearance of satellite peaks in the Cu 2p spectra, however, provided definitive evidence for the presence of Cu²⁺ ions in these studied samples as well. Doping-induced PL quenching was observed due to the absorption of energy from defect emission in the V⁵⁺ lattice by Cu²⁺ ions. We have proposed a cost-effective, less complicated but effective way of synthesizing pure and doped samples in colloidal form, deposited by the nebulizer spray technique on p-Si to establish junction diodes with enhanced optoelectronic properties.

A wet chemical precipitation method was used to synthesize pure and Cu-doped (3, 5 or 7 at%) V₂O₅ nanorods and photodiodes were fabricated.     

Continuous selective deoxygenation of palm oil for renewable diesel production over Ni catalysts supported on Al2O3 and La2O3–Al2O3

The present study provides, for the first time in the literature, a comparative assessment of the catalytic performance of Ni catalysts supported on γ-Al₂O₃ and γ-Al₂O₃ modified with La₂O₃, in a continuous flow trickle bed reactor, for the selective deoxygenation of palm oil. The catalysts were prepared via the wet impregnation method and were characterized, after calcination and/or reduction, by N₂ adsorption/desorption, XRD, NH₃-TPD, CO₂-TPD, H₂-TPR, H₂-TPD, XPS and TEM, and after the time-on-stream tests, by TGA, TPO, Raman and TEM. Catalytic experiments were performed between 300–400 °C, at a constant pressure (30 bar) and different LHSV (1.2–3.6 h⁻¹). The results show that the incorporation of La₂O₃ in the Al₂O₃ support increased the Ni surface atomic concentration (XPS), affected the nature and abundance of surface basicity (CO₂-TPD), and despite leading to a drop in surface acidity (NH₃-TPD), the Ni/LaAl catalyst presented a larger population of medium-strength acid sites. These characteristics helped promote the SDO process and prevented extended cracking and the formation of coke. Thus, higher triglyceride conversions and n-C₁₅ to n-C₁₈ hydrocarbon yields were achieved with the Ni/LaAl at lower reaction temperatures. Moreover, the Ni/LaAl catalyst was considerably more stable during 20 h of time-on-stream. Examination of the spent catalysts revealed that both carbon deposition and degree of graphitization of the surface coke, as well as, the extent of sintering were lower on the Ni/LaAl catalyst, explaining its excellent performance during time-on-stream.

Highly selective and stable Ni supported on La₂O₃–Al₂O₃ catalyst on the deCO/deCO₂ reaction paths for the production of renewable diesel.     

Nb-doped and Al2O3 + B2O3-coated granular secondary LiMn2O4 particles as cathode materials for lithium-ion batteries

In this work, to improve the cyclability and high-temperature performance of cubic spinel LiMn₂O₄ (LMO) as cathode materials, Nb⁵⁺-doped LiMn₂O₄ powders coated and uncoated with Al₂O₃ and/or B₂O₃ were synthesized via the modified solid-state reaction method. It was found that Nb⁵⁺-doped and B₂O₃ + Al₂O₃-coated LMO powders comprising 5 μm granular agglomerated fine primary particles smaller than 350 nm in diameter exhibited superior electrochemical properties with initial discharge capacity of 101.68 mA h g⁻¹; we also observed capacity retention of 96.31% after 300 cycles at room temperature (RT) and that of 98% after 50 cycles at 55 °C and 1C rate.

Nb-doped and Al₂O₃ + B₂O₃-coated granular secondary LMO particles enabling superior cycling performance at 25 and 55 °C.     

Tb3+ and Sm3+ co-doped Ca2La3(SiO4)3F phosphor: synthesis,color regulation,and luminescence properties

The polychromatic phosphor with an apatite structure Ca₂La₃(SiO₄)₃F:0.15Tb³⁺,xSm³⁺ (CLSOF:0.15Tb³⁺,xSm³⁺) was synthesized via a solid-state route. The phase and morphology of the phosphor has been investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The structures of the as-prepared phosphor were verified by means of the Rietveld method. The optical performance was investigated thoroughly and the phosphors could emit multicolor light from short wavelengths to long wavelengths by gradually increasing the doping contents of samarium. All the results support that the energy transfer in CLSOF:0.15Tb³⁺,xSm³⁺ contributes to the color tunable property of the phosphor.

The photoluminescence spectra of Ca₂La_2.85−x(SiO₄)₃F:0.15Tb³⁺,xSm³⁺ phosphors (left) could emit typical multicolor light with increasing doping contents of samarium (right).     

Highly active postspinel-structured catalysts for oxygen evolution reaction

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides LaBO₃ and spinel oxides ZnB₂O₄. Electrochemical impedance spectroscopy reveals that the higher OER activities for CaB₂O₄ series are attributed to the lower charge-transfer resistances. A density-functional-theory calculation proposes a novel mechanism associated with lattice oxygen pairing with adsorbed oxygen, demonstrating the lowest theoretical OER overpotential than other mechanisms examined in this study. This finding proposes a structure-driven design of electrocatalysts associated with a novel OER mechanism.

Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited systematically higher catalytic activities in the oxygen evolution reaction (OER) than nominally conventional counterparts of perovskite LaBO₃ and spinel ZnB₂O₄.     

Size dependent optical temperature sensing properties of Y2O3: Tb3+, Eu3+ nanophosphors

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The sizes of the sample particles were controlled by changing the molar ratio of the urea and rare earth ions. The microstructure and crystallographic structure of the sample were determined through powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FE-SEM). The test results show that the sample is body centered cubic. As the molar ratio of urea to rare earth ions increases, the size of the sample particles decreases. The temperature-dependent emission spectra of Tb³⁺, Eu³⁺ co-doped Y₂O₃ phosphors with different particle sizes were measured. The results showed that because the fluorescence intensity ratio (FIR) of Tb³⁺ and Eu³⁺ varies with temperature, it can be used to visually reflect changes in temperature. In addition, the temperature sensing sensitivity of Tb³⁺ and Eu³⁺ co-doped Y₂O₃ phosphors increased upon a decrease in the particle size, but the relative sensitivity decreased with a decrease in the particle size. The physical mechanism of the sensitivity and relative sensitivity changes with the size of the sample particles was also explained.

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The size dependence-optical temperature sensing properties of nanophosphors have been studied.     

Synthesis,electronic structures,and photoluminescence properties of an efficient and thermally stable red-emitting phosphor Ca3ZrSi2O9:Eu3+,Bi3+ for deep UV-LEDs

A series of red-emitting Ca₃ZrSi₂O₉:Eu³⁺,xBi³⁺ phosphors was synthesized using a conventional high temperature solid-state reaction method, for the purpose of promoting the emission efficiency of Eu³⁺ in a Ca₃ZrSi₂O₉ host. The site preference of Bi³⁺ and Eu³⁺ in the Ca₃ZrSi₂O₉ host was evaluated by formation energy. The effects of Bi³⁺ on electronic structure, luminescent properties, and related mechanisms were investigated. The inner quantum yield of the optimized sample increased to 72.9% (x = 0.08) from 34.6% (x = 0) at 300 nm ultraviolet light excitation. The optimized sample (x = 0.08) also showed excellent thermal stability, and typically, 84.2% of the initial emission intensity was maintained when the temperature increased to 150 °C from 25 °C, which is much higher than that without Bi³⁺ doping (70.1%). The mechanisms of emission properties and thermal stability enhancement, as well as the redshift of the charge transfer band (CTB) induced by Bi³⁺ doping in the Ca₃ZrSi₂O₉:Eu³⁺ phosphor, were discussed. This study elucidates the photoluminescence properties of Bi³⁺-doped Ca₃ZrSi₂O₉:Eu³⁺ phosphor, and indicates that it is a promising luminescent material that can be used in ultraviolet light-emitting diodes.

A red-emitting phosphor Ca₃ZrSi₂O₉:Eu³⁺,Bi³⁺ with high quantum yield and thermal stability was developed by introducing Bi³⁺ as an efficient sensitizer.     

Novel SrMg2La2W2O12:Mn4+ far-red phosphors with high quantum efficiency and thermal stability towards applications in indoor plant cultivation LEDs

Novel Mn⁴⁺-activated far-red emitting SrMg₂La₂W₂O₁₂ (SMLW) phosphors were prepared by a conventional high-temperature solid-state reaction method. The SMLW:Mn⁴⁺ phosphors showed a broad excitation band peaking at around 344 nm and 469 nm in the range of 300–550 nm. Under 344 nm near-ultraviolet light or 469 nm blue light, the phosphors exhibited a far-red emission band in the 650–780 nm range centered at about 708 nm. The optimal Mn⁴⁺ doping concentration in the SMLW host was 0.2 mol% and the CIE chromaticity coordinates of SMLW:0.2% Mn⁴⁺ phosphors were calculated to be (0.7322, 0.2678). In addition, the influences of crystal field strength and nephelauxetic effect on the emission energy of Mn⁴⁺ ions were also investigated. Moreover, the internal quantum efficiency of SMLW:0.2% Mn⁴⁺ phosphors reached as high as 88% and they also possessed good thermal stability. Specifically, the emission intensity at 423 K still maintained about 57.5% of the initial value at 303 K. Finally, a far-red light-emitting diode (LED) lamp was fabricated by using a 365 nm near-ultraviolet emitting LED chip combined with the as-obtained SMLW:0.2% Mn⁴⁺ far-red phosphors.

Novel Mn⁴⁺-activated SrMg₂La₂W₂O₁₂ far-red emitting phosphors with an internal quantum efficiency as great as 88% and excellent thermal stability were prepared towards applications in indoor plant cultivation LEDs.     

Fabrication of La3+ doped Ba1−xLaxTiO3 ceramics with improved dielectric and ferroelectric properties using a composite-hydroxide-mediated method

Lanthanum (La³⁺) doped Ba_1−xLa_xTiO₃ (x = 0.0, 0.0025, 0.005, 0.0075) ceramics were synthesized by the composite-hydroxide-mediated method. Rietveld refinement of the XRD patterns confirmed the formation of a perovskite crystal structure that transforms from tetragonal to pseudo-cubic with La³⁺ doping content (x). Scanning electron microscopy displayed a dense and homogeneous microstructure with reduced grain size on La³⁺ doping. The frequency and temperature-dependent dielectric measurements showed an improvement in the dielectric permittivity, a decrease in the ferroelectric–paraelectric transition temperature, and an increase in the dielectric diffusivity with increasing La³⁺ doping content. Complex impedance analysis indicated the semiconducting behavior with a positive temperature coefficient of resistance effect, which could be explained in terms of a charge compensation mechanism in the donor doped BaTiO₃. The ferroelectric hysteresis loops revealed that these ceramics are ferroelectric in nature, while an improvement in the energy storage density and energy storage efficiency was observed for the doped samples due to reduced grain size on La³⁺ doping. Here, the sample with x = 0.005 has a high dielectric permittivity, a low dielectric tangent loss, and the highest energy storage efficiency. This makes this composition interesting for energy storage applications.

The improved dielectric and energy storage properties of La³⁺-doped BaTiO₃ ceramics make them attractive for use in energy storage applications.