Sites occupancy preference of Bi3+ and white light emission through co‐doped Sm3+ in LiGd5P2O8

Bi³⁺, Sm³⁺‐activated LiGd₅P₂O₈ (LGPO) phosphors were prepared through high‐temperature solid‐state method. In LGPO host, there are 5 types of Gd crystallographic sites, named as Gd(1)/Gd(2)/Gd(3)/Gd(4), and Gd(5). Bi³⁺‐activated LGPO phosphors exhibit 1 broad excitation band from 250 to 320 nm centered at 293 nm and a broad asymmetric emission band ranging from 350 to 600 nm with the maximum value approximately at 409 nm. It can be concluded from dual‐emission spectra that Bi³⁺ may occupy 2 Gd sites and an obvious spectral blue‐shift appeared with increasing Bi³⁺ content, which is caused by the intensity of crystal field of Bi³⁺ is decreased. Notably, through the calculation of each Gd‐O chemical parameter, the environmental factor (h_e) value of each Gd site can be obtained and it can be further inferred that 2 emission bands centered at 409/461 nm are ascribed to Bi³⁺ ions which occupies Gd(3) and Gd(4) sites, respectively. Energy transfer from Bi³⁺ to Sm³⁺ ions in Bi³⁺/Sm³⁺ co‐doped LGPO samples occurred and it realizes the color‐tunable emission from cyan to yellow including white‐light emission, through controlling Sm³⁺ content. Moreover, energy transfer mechanism between Bi³⁺ and Sm³⁺ ions is verified to be dipole‐dipole interaction by analyzing the spectroscopic experimental results and the critical distance between them is calculated to be 8.22 Å by concentration quenching method. Finally, it is illustrated that Bi³⁺ and Sm³⁺ co‐doped LGPO phosphors will be a promising candidate for n‐UV chip pumped w‐LEDs.     

Highly-doped YAG:Sm3+ transparent ceramics: Effect of Sm3+ ions concentration

YAG:Sm³⁺ (3–15 at.%) transparent ceramics, a promising cladding material for suppressors of parasitic oscillations at 1064 nm of YAG:Nd³⁺ lasers, have been prepared by solid-state reactive sintering at 1725 °C. The effect of samarium ions concentration on the microstructure and optical properties of YAG:Sm³⁺ sintered ceramics was studied for the first time. The solubility limit of samarium ions in the garnet matrix was found to lie within the range of 9–11 at.%. The spectroscopic characterization of YAG:Sm³⁺ (3–15 at.%) ceramic samples showed that the absorption coefficients corresponding to Sm³⁺ ions transitions increased linearly with increasing Sm³⁺ doping. Also, the increase in the concentration of Sm³⁺ ions contributes to the increase in the intensities of the satellites, leading to the broadening of the main spectral lines and implicitly to the increase of the absorption coefficient around 1064 nm. It was shown that YAG:Sm³⁺ ceramics doped with 9 at.% Sm³⁺ ions possess optical losses of 0.07 cm^?1 at 808 nm and an optical absorption coefficient of 4.45 cm^?1 at 1064 nm. The concentration dependence of the ⁴G_5/2 level decay confirmed that the luminescence extinction is due to the energy transfer between the Sm³⁺ ions through cross-relaxation processes. All these results show that highly-doped YAG:Sm³⁺ (9 at.%) ceramics could be the best candidate for parasitic oscillation suppression in high-power YAG:Nd³⁺ lasers at 1064 nm.     

White luminescence of bismuth and samarium codoped Y2O3 phosphors

In this work Sm³⁺ (0–2.0 at%) and Bi³⁺ (0–2.0 at%) doped Y₂O₃ luminescent powders were prepared by a sol–gel method from yttrium acetylacetonate, samarium and bismuth nitrates as metal sources. The as prepared powders (chemical composition is close to stoichiometric Y₂O₃) present the cubic structure from 700 °C, and at 900 °C are characterized by the presence of rounded particles with heterogeneous size of 42.9 nm. Luminescent effect of ions of Sm³⁺ and Bi³⁺ into Y₂O₃ host as was studied on heat treated powders from 800 to 1100 °C. The combination of the red luminescence from the Sm³⁺ ions and the bluish from Bi³⁺, makes the synthesized phosphors candidates to be used in fabrication of phosphor-converted light-emitting diodes (LEDs).     

Synthesis and Characterization of Eu3+‐Doped Transparent Glass–ceramics Containing Nanocrystalline SrIINbIVO3

The glass–ceramics containing a rarely achievable nanocrystalline Sr^IINb^IVO₃ phase in the 53.75SiO₂–18.25K₂O–9Bi₂O₃–9SrO–9Nb₂O₅–0.5CeO₂–0.5Eu₂O₃ (mol%) glass system were prepared by the melt‐quench technique followed by a two‐stage controlled heat treatment. The unusual oxidation state of Nb in Sr^IINb^IVO₃ crystal is 4+ and upon heat treatment of the samples at lower temperature of 500°C for several hours, the glass composition and chemical environment around Nb ions played a key role for the formation of Sr^IINb^IVO₃ in the glass–ceramics. The microstructure of the glass–ceramics was studied using TEM and FESEM. The TEM images advocate 10–40 nm crystallite size of Sr^IINb^IVO₃. FTIR study confirms that all the samples consist of SiO₄, BiO₃, BiO₆, and NbO₆ structural units. The refractive index at different wavelengths was found to vary in the range 1.7105–1.7905 and increase with increase in heat‐treatment time. The luminescence spectra of Eu³⁺‐doped glass and glass–ceramics were recorded at 465 nm excitation wavelength and the luminescence intensity is found to be increased with heat‐treatment time due to increase in crystallinity. The high intensity ratio of ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁ indicates that the Eu³⁺‐doped nanocrystalline Sr^IINb^IVO₃ glass–ceramics are promising candidate materials as red‐light source.     

Hierarchical growth of BiOCl on SrO‐Bi2O3‐B2O3 glass‐ceramics for self‐cleaning applications

We have grown hierarchical structure of bismuth oxycloride (BiOCl) on SrO‐Bi₂O₃‐B₂O₃ (SBBO) transparent glass‐ceramic. SBBO glass‐ceramics were fabricated via conventional melt‐quenching technique while BiOCl was grown by etching the glass via HCl. Enhanced visible light driven photocatalytic activity and increasing hydrophobic feature were observed on BiOCl grown SBBO than as‐quenched SBBO glass‐ceramics. Contact angle analysis showed maximum contact angle of 130.7° on the surface of most BiOCl grown SBBO glass‐ceramic. Furthermore, under visible light illumination water contact angle decreased from 130.7° to 30.8°. Such photo‐induced hydrophilicity and catalytic performance in translucent glass‐ceramics lead self‐cleaning applications.     

New Sintered Li2O–Al2O3–SiO2 Ultra‐Low Expansion Glass‐Ceramic

We developed a new Li₂O–Al₂O₃–SiO₂ (LAS) ultra‐low expansion glass‐ceramic by nonisothermal sintering with concurrent crystallization. The optimum sintering conditions were 30°C/min with a maximum temperature of 1000°C. The best sintered material reached 98% of the theoretical density of the parent glass and has an extremely low linear thermal expansion coefficient (0.02 × 10^?6/°C) in the temperature range of 40°C–500°C, which is even lower than that of the commercial glass‐ceramic Ceran^® that is produced by the traditional ceramization method. The sintered glass‐ceramic presents a four‐point bending strength of 92 ± 15 MPa, which is similar to that of Ceran^® (98 ± 6 MPa), in spite of the 2% porosity. It is white opaque and does not have significant infrared transmission. The maximum use temperature is 600°C. It could thus be used on modern inductively heated cooktops.     

Red-emitting enhancement of Bi4Si3O12:Sm3+ phosphor by Pr3+ co-doping for White LEDs application

In this account, Bi₄Si₃O₁₂:Sm³⁺ and (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr³⁺ ions on red emission properties of Bi₄Si₃O₁₂:Sm³⁺ phosphors, as well as the mechanism of interaction between Sm³⁺ and Pr³⁺ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at λ_ex=403 nm were similar to those of Bi₄Si₃O₁₂:Sm³⁺ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the ⁴G_5/2→⁶H_7/2 transition of the Sm³⁺ ion. The photoluminescence intensities of Bi₄Si₃O₁₂:Sm³⁺ phosphors were significantly improved by co-doping with Pr³⁺ ions and were maximized at Sm³⁺ and Pr³⁺ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm³⁺ ions were displayed in the emission spectra of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at respectively λ_ex=443 nm and λ_ex=481 nm (Pr:³H₄→³P₂, ³H₄→³P₀). This indicated the existence of Pr³⁺→Sm³⁺ energy transfer in (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors.     

Microstructural,ferroelectric, and photoluminescent properties of (100)‐oriented Sm3+‐doped Na0.5Bi0.5TiO3 thin films

(100)_C‐oriented Na_0.5Bi_0.5‐xSm_xTiO₃ (NBST) lead‐free ferroelectric thin films were prepared on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method, and their microstructural, dielectric, ferroelectric, and photoluminescent properties were studied. X‐ray diffraction and scanning electron microscopy analysis indicated that both the grain size and (100)_C orientation degree of NBST thin films were decreased by doping Sm³⁺ ions. Raman spectra showed that structural symmetry of NBST thin films decreased at low Sm³⁺ doping concentration and then increased at high doping concentration of Sm³⁺ ions. An appropriate amount of Sm³⁺ dopants was confirmed to enhance dielectric and ferroelectric properties of the NBST thin films. Among all the compositions, the Na_0.5Bi_0.492Sm_0.008TiO₃ thin film exhibited the largest remnant polarization (2P_r) of 27.3 μC/cm² and high dielectric constant of 1068, as well as a low dielectric loss of 0.04. Temperature‐ and frequency‐dependent dielectric characteristics illustrated the relaxor ferroelectric behavior of Na_0.5Bi_0.492Sm_0.008TiO₃ thin film. Meanwhile, the Na_0.5Bi_0.492Sm_0.008TiO₃ thin film also showed optimal orange‐red emission at 600 nm, which is originating from the ⁴G_5/2 → ⁴H_7/2 transition of Sm³⁺ ions.     

Near white light emission of Ce3+‐, Ho3+‐, and Sm3+‐doped oxyfluoride silicate glasses

The Ce³⁺‐, Ho³⁺‐, and Sm³⁺‐ single and co‐doped oxyfluoride silicate glasses for light emitting diodes are studied. These glasses were prepared by melt quenching method and their optical and structural properties were investigated by absorption spectra, photoluminescence spectra, Commission International de I'Eclairage chromaticity coordinates, X‐ray diffraction, and Fourier transform infrared spectra. It is found that the introduction of Al₂O₃ in glass composition can improve the emissions of Ho³⁺ and Sm³⁺. While the presence of B₂O₃ has the adverse effect and can suppress the emissions of Ho³⁺ and Sm³⁺. With substituting Na₂O for CaO in the glass compositions, CaF₂ crystals can be formed during the melt quenching process. We find the formation of CaF₂ crystals can change the emission behavior of Ho³⁺ and Sm³⁺ ions. White light emissions can be achieved in the glasses and the luminescence colors can be tuned by varying the concentrations of the doped rare‐earth ions and the composition of glass matrix. The Ce³⁺‐, Ho³⁺‐, and Sm³⁺‐doped oxyfluoride silicate glasses presented here demonstrate promising applications in the fields of light emitting diodes.     

Synthesis of Eu3+‐doped BaBi2Ta2O9 based glass‐ceramic nanocomposites: Optical and dielectric properties

In this paper we report for the first time synthesis of Eu³⁺‐doped transparent glass‐ceramics (TGC) with BaBi₂Ta₂O₉ (BBT) as the major crystal phase using the glass system SiO₂–K₂O–BaO–Bi₂O₃–Ta₂O₅ by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat‐treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE‐SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass‐ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu³⁺ was observed due to incorporation of Eu³⁺ ions into the low‐phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε_r), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency.     

Er3+ Ions‐Doped Germano‐Gallate Oxyfluoride Glass‐Ceramics Containing BaF2 Nanocrystals

Er³⁺ ions‐doped germano‐gallate oxyfluoride glass‐ceramic containing BaF₂ nanocrystals was prepared through conventional melt quenching and subsequent thermal treatment method. X‐ray diffraction patterns and transmission electron microscope images confirmed the formation of BaF₂ nanocrystals in glass‐ceramics. Preferential incorporation of Er³⁺ ions into the BaF₂ nanocrystals were confirmed by the absorption spectra and emission spectra, and enhanced upconversion emission and infrared emission were observed. Relatively high transmittance in the mid‐infrared region indicated great potential of this germano‐gallate oxyfluoride glass‐ceramics as host materials for the efficient mid‐infrared emission from rare‐earth ions.     

Nd3+/Sm3+ codoped NaLa(WO4)2 glass ceramic: A novel optical heater

Transparent Nd³⁺/Sm³⁺ codoped tungstate silicate glass ceramics were prepared and used for the photothermal conversion process. XRD patterns, TEM image and the enhanced Raman signals confirm the appearance of the tetragonal scheelite NaLa(WO₄)₂ nanocrystals in the vitreous phase. In comparison to the precursor glass, the enhancement of photoluminescence of Nd³⁺ ions in the glass ceramics attributes to the enrichment of Nd³⁺ ion in the precipitated low phonon-energy tetragonal scheelite NaLa(WO₄)₂ nanocrystals. The rapid reduction of photoluminescence of Nd³⁺ ions in the Nd³⁺/Sm³⁺ codoped glass ceramics demonstrates that a strong energy transfer from Nd³⁺ to Sm³⁺ takes place, which provides more non-radiative relaxation channels and is beneficial for the improving the photothermal conversion efficiency. Under the irradiation of 808 nm laser diode, a significant temperature rise is observed in the Nd³⁺/Sm³⁺ codoped glass ceramics and may be used as a good optical heater.     

Enhanced Sunlight Excited 1‐μm Emission in Cr3+–Yb3+ Codoped Transparent Glass‐Ceramics Containing Y3Al5O12 Nanocrystals

Cr³⁺–Yb³⁺ codoped transparent glass‐ceramics containing Y₃Al₅O₁₂ nanocrystals were prepared by heat treatment of as‐prepared glass sample and characterized by X‐ray diffraction and transmission electron microscopy. The efficient energy transfer from Cr³⁺ to Yb³⁺ ions through multi‐phonon‐assisted process was confirmed by the luminescence spectrum and fluorescent lifetime measurements. When excited by the lights from a solar simulator in the wavelength region of 400–800 nm, greatly enhanced near‐infrared emission around 1 μm was achieved from Cr³⁺–Yb³⁺ codoped glass ceramic compared with that from as‐prepared glass and Ce³⁺–Yb³⁺ codoped glass ceramic. These results demonstrate that the Cr³⁺–Yb³⁺ codoped glass ceramic is a promising material for enhancement of the efficiency of solar energy utilization.     

Aerosol Codeposition of Ceramics: Mixtures of Bi2O3–TiO2 and Bi2O3–V2O5

Aerosol deposition (AD) is a promising method to apply ceramic films on a wide range of substrate materials. Until now, AD has mainly been performed using a single ceramic powder. In this work, mixtures of two different ceramic powders were prepared. The first mixture consisted of Bi₂O₃ and TiO₂ and the second consisted of Bi₂O₃ and V₂O₅, in stoichiometric ratios to form Bi₄Ti₃O₁₂ and Bi₄V₂O_11?δ, respectively. Aerosol codeposition produced films with homogeneously distributed particle fractions and thicknesses between 10 and 100 μm. Composite films were annealed to temperatures up to 750°C to enable an in situ calcination and attempted formation of the above‐mentioned compounds. Successful formation of Bi₄Ti₃O₁₂ was tracked by hot‐stage X‐ray diffraction (XRD), and confirmed by dielectric measurements. Formation of the intended Bi₄V₂O_11?δ, on the other hand, was not achieved, but rather BiVO₄, which was confirmed by XRD, EDX and electrical measurements. The bismuth deficiency occurred during spray deposition, and is attributed to powder/material characteristics. Additional insight about the AD process is gained by comparing mixtures of oxides with different relative hardness values. Aerosol codeposition of ceramics may be an interesting new technique for producing porous functional ceramics.     

Effect of Sm3+ doping on ferroelectric,energy storage and photoluminescence properties of BaTiO3 ceramics

Rare earth doped ferroelectric ceramics have attracted much attention due to their great potential application for novel multifunctional optical-electro devices. Herein, the x% mol Sm³⁺ doped BaTiO₃ (BTO:xSm³⁺) ceramics were fabricated by the conventional solid-state reaction method. The Sm³⁺ ions composition dependent phase structure, ferroelectric, energy storage and photoluminescence properties were systematically investigated. With the increase of Sm³⁺ ions composition, the remanent polarization decreases dramatically from 15.705 μC/cm² (BTO) to 7.132 μC/cm² (BTO:3.0%Sm³⁺), but the energy storage density and efficiency increase greatly with a relative change of 79.76% and 31.13%, respectively. Furthermore, Sm³⁺ doping causes the transformation from the tetragonal to pseudo-cubic phase for BTO ceramics at room temperature, resulting in a broader temperature transition range from the ferroelectric to paraelectric phase and a lower Curie temperature. Particularly, the pure BTO and BTO:xSm³⁺ ceramics show great thermal stability for energy storage properties. In addition, under the excitation of 408 nm near-ultraviolet light, the BTO:xSm³⁺ ceramics exhibit the strongest orange-red emission peak around 596 nm with a large relative tunability of intensity by 88.97%. The results suggest that the BTO:xSm³⁺ ceramics are suitable for the design of optoelectronic devices.     

Synthesis and photoluminescent properties of Sm3+-doped SnO2 nanoparticles

SnO₂ ceramic nanoparticles homogeneously doped with Sm³⁺ ions were synthesized via a sol-gel method, followed by drying and annealing in air. X-ray diffractometry, FT-IR spectrometry and transmission electron microscopy were used to characterize the nanoparticulate samples. After annealing, both doped and undoped SnO₂ nanopowders were shown to adopt the rutile tetragonal crystal form and to exhibit characteristic Sn–O–Sn vibrations. The average particle size was found to be in the region of 23–28 nm. Photoluminescence analysis at room temperature demonstrated strong enhancement of the visible emission from Sm³⁺, via energy transfer from the SnO₂ host matrix to the dopant. The maximum emission efficiency was observed for a concentration of 1.5 atom% Sm³⁺.     

Characterization of Bi2O3 thin films for doping photoluminescent Er3+ ions

Undoped and Er³⁺-doped Bi₂O₃ thin films were sputter-deposited on Si(100) substrates. Sufficiently oxidized Bi₂O₃ films with refractive indices between 2.17?2.23 were obtained at a wavelength of 633 nm; these values are comparable to those of bulk Bi₂O₃ crystals. While the film composition was stable for deposition temperatures between room temperature (RT) and 450 °C, the refractive index steeply decreased above 450 °C and reached 1.4 at 600 °C. The lowering of the optical transmittance spectra indicated aggregation of metallic Bi and darkening of the film. All films exhibited X-ray diffraction patterns of α-Bi₂O₃. The direct and indirect bandgap energies derived from the Tauc plots were 3.4–3.7 eV and 1.9–2.5 eV, respectively, depending on the O₂ flow rate and deposition temperature. Upon excitation of Er³⁺-doped Bi₂O₃ films at 532 nm, Er³⁺ emissions peaking at 1537 and 1541 nm appeared, and the photoluminescence spectra included fine structures reflecting crystal-field splitting. Resonant excitation of Er³⁺ 4f levels and indirect excitation via the defect levels of Bi₂O₃ followed by energy transfer to Er³⁺ contributed to the emission. The films deposited at RT with Er concentrations of 2 at.% had the emission intensity of Er³⁺, but concentration quenching strongly suppressed the Er³⁺ emission because the doped Er³⁺ ions stayed inside the Bi₂O₃ crystals. At deposition temperatures above 400 °C, the concentration quenching was mitigated possibly because out-diffusion of Er³⁺ ions reduced the effective number of Er³⁺ ions in the Bi₂O₃ crystalline domains.     

Enhanced Up‐Conversion Luminescence in Er3+‐Doped 25GeS2·35Ga2S3·40CsCl Chalcogenide Glass–Ceramics

Enhanced luminescence in rare‐earth‐doped chalcogenide glass–ceramics is of great interest for the potential integrated optoelectronic devices. However, fundamental mechanism on the enhancement of luminescence upon crystallization remains largely unknown. We report the fabrication and characterization of wide transmission chalcogenide glass and glass–ceramics based on the 25GeS₂·35Ga₂S₃·40CsCl:0.3Er glass composition, and discuss the mechanism of enhanced luminescence. By monitoring the ⁴I_9/2–⁴I_15/2 of Er³⁺ transition, up‐conversion luminescence of 12 times higher was observed in glass–ceramics compared with that in base glass. Electron paramagnetic resonance (EPR) and Raman scattering spectroscopies were employed to obtain the information of selective environment of Er³⁺ ions and microstructural evolution with the crystallization progress. Both of them evidenced that the enhanced up‐conversion luminescence was mainly related to the local environmental evolution from a mixed chlorine‐sulfur coordination to a low phonon energy chlorine coordination in the residual glassy matrix of glass–ceramics.     

White‐Light and Yellow/Blue Photoluminescence Emission Based on Dy3+‐Doped SiO2–Gd2O3 Composites

This work attempts to obtain Dy³⁺‐doped SiO₂–Gd₂O₃ by sol–gel process_, with a molar ratio of 70Si⁴⁺–30Gd³⁺ and Dy³⁺ concentrations of 0.1, 0.3, 0.5, and 1 mol%. Heat treatment at temperatures of 1000°C, 1100°C, 1200°C, and 1300°C have been performed. From XRD, the Gd₂O₃ cubic phase was observed at 1000°C and 1100°C, at 1200°C also were observed Gd₂O₃ monoclinic phase, predominant at 1300°C. The band‐gap values vary between 4.4 and 5.3 eV, showing dependence on the crystalline phase. Under UV excitation, emission spectra show bands assigned to the Dy³⁺ transitions: ⁴F_9/2→⁶H_15/2 (484 nm), ⁴F_9/2→⁶H_13/2 (572 nm), and ⁴F_9/2→⁶H_11/2 (668 nm). The excitation at 275 nm has shown more effective. The ratio between the most intense emission bands (yellow/blue) show values around 0.84 and 1.63. CIE chromaticity diagrams show color coordinates at blue, yellow, and white regions, as a function of Dy³⁺ concentration and heat treatment. The lifetime values of excited state ⁴F_9/2 were around 0.20 and 0.69 ms. The morphology of particles changed from spherical to coral‐like shape as a function of heat treatment are observed. The sol–gel process showed to be an interesting route to obtain Dy³⁺‐doped binary system materials.     

Anti-reduction of Ti4+ in Ba4.2Sm9.2Ti18O54 ceramics by doping with MgO,Al2O3 and MnO2

The anti-reduction of Ti⁴⁺ ions in Ba_4.2Sm_9.2Ti₁₈O₅₄ (BST) ceramics at high sintering temperature over 1300 °C was investigated. MgO, Al₂O₃ and MnO₂ were added separately to suppress the reduction of Ti⁴⁺ ions so as to improve the microwave dielectric properties of BST ceramics. The microstructure of BST ceramics was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used to study the electroconductivity of BST ceramics and valency changes of Ti ions. The results showed that MgO or Al₂O₃, when acting as an acceptor, could effectively suppress the reduction of Ti⁴⁺ ions and significantly improve the Q × f values of BST ceramics at the cost of dielectric constant. Meanwhile, MnO₂ as an oxidant had also improved the Q × f values but with no decrease in dielectric constant. Excellent microwave dielectric properties were achieved in Ba_4.2Sm_9.2Ti₁₈O₅₄ ceramics doped with 0.2 wt.% Al₂O₃ sintered at 1340 °C for 3 h: ?_r = 76.9, Q × f = 10,120 GHz and τ_f  = ?22.7 ppm/°C.