Preparation of Mn2+-Cu+ co-doped P2O5–ZnO–Al2O3 glasses and their red fluorescence properties

To make a Mn²⁺-doped red glass phosphor that can be excited with ultraviolet (UV) light of light-emitting diodes (LEDs), 60P₂O₅-35ZnO-5Al₂O₃-8MnO-xCu₂O glasses (x = 0-1.00) were prepared by a melt-quenching method at 1200-1400°C for 30-180 minutes in atmospheric air, and the redox of Mn and Cu as well as fluorescence properties were investigated. The Mn²⁺ ion was not reduced and oxidized in the melting, quenching, and annealing processes. The valence of Cu in the glasses changed in the order of 0, 1+, and 2+ with the increase in the amount of Cu₂O and in the melting temperature and time. In this study, a 60P₂O₅-35ZnO-5Al₂O₃-8MnO-0.10Cu₂O glass melted at 1250°C for 90 minutes, having the highest Cu⁺ concentration, showed the strongest Mn²⁺ red fluorescence under the UV light at 275 nm. This strong Mn²⁺ red fluorescence has been caused by the energy transfer from excited Cu⁺ ions to Mn²⁺ ions.     

A Single‐Phased Sr1−y‐3x/2Al2Si2O8: xCe3+, yMn2+ with Efficient Energy Transfer as a Potential Phosphor for White‐Light‐Emitting Diodes

A series of Ce³⁺‐ and Mn²⁺‐(co‐)activated SrAl₂Si₂O₈ phosphors have been prepared at 1350°C under a reducing atmosphere and their photoluminescence properties have been studied as a function of the (co‐)dopant ions concentrations. We have discovered that energy transfer (ET) not only from Ce³⁺ to Mn²⁺ but also from “defects” to Mn²⁺ by the facts that there is existing significant overlap between the emission spectrum of Ce³⁺ (“defects”) and the excitation spectrum of Mn²⁺. The source of the “defects” in the host lattice is originated from the different charge substitution between Ce³⁺ and Sr²⁺. By adopting the principle of ET, the material SrAl₂Si₂O₈: Ce, Mn can act as a phosphor for white‐light ultraviolet light‐emitting diodes (UV‐LEDs) by tuning of the dopants contents.     

A single‐phase full‐color emitting phosphor Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ with near‐zero thermal quenching and high quantum yield for near‐UV converted warm w‐LEDs

A single‐phase full‐color emitting phosphor Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ has been synthesized by high‐temperature solid‐state method. The crystal structure is measured by X‐ray diffraction. The emission can be tuned from blue to green/red/white through reasonable adjustment of doping ratio among Eu²⁺/Tb³⁺/Mn²⁺ ions. The photoluminescence, energy‐transfer efficiency and concentration quenching mechanisms in Eu²⁺‐Tb³⁺/Eu²⁺‐Mn²⁺ co‐doped samples were studied in detail. All as‐obtained samples show high quantum yield and robust resistance to thermal quenching at evaluated temperature from 30 to 200°C. Notably, the wide‐gamut emission covering the full visible range of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ gives an outstanding thermal quenching behavior near‐zero thermal quenching at 150°C/less than 20% emission intensity loss at 200°C, and high quantum yield‐66.0% at 150°C/56.9% at 200°C. Moreover, the chromaticity coordinates of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ keep stable through the whole evaluated temperature range. Finally, near‐UV w‐LED devices were fabricated, the white LED device (CCT = 4740.4 K, Ra = 80.9) indicates that Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ may be a promising candidate for phosphor‐converted near‐UV w‐LEDs.     

Influence of Crystallization on the Conversion of Sm3+→Sm2+ in SrO–Bi2O3–K2O–B2O3 Glass‐Ceramics

Sm³⁺‐doped glass 13SrO–2Bi₂O₃–5K₂O–80B₂O₃ was fabricated by the conventional melt‐quenching technique. The glass‐ceramics were obtained by heating the as‐prepared glasses in air atmosphere at selected temperatures 550°C, 600°C, 615°C, and 650°C, respectively. The luminescence spectra of both Sm³⁺ and Sm²⁺ were detected in the ceramic heated at 650°C where crystalline phase is formed. The as‐prepared glass and the ceramics heated at 550°C, 600°C, and 615°C show only the emission due to Sm³⁺. In the sample heated at 650°C in air atmosphere, however, part of Sm³⁺ ions was converted to Sm²⁺, giving rise to sharp emission lines which are characteristic of Sm²⁺ in crystalline state. It is suggested that Sm²⁺ ions are located at Sr²⁺ site in the ceramic while Sm³⁺ ions are located at Bi³⁺ sites. The Sm²⁺‐doped glass‐ceramic has a high optical stability because the fluorescence intensity decreases by only about 8% of its initial value upon excitation at 488 nm Ar⁺ laser.     

Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.     

Orderly‐Layered Tetravalent Manganese‐Doped Strontium Aluminate Sr4Al14O25:Mn4+: An Efficient Red Phosphor for Warm White Light Emitting Diodes

Searching for an efficient non rare earth‐based oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm and unexcitable by green light, is essential for the development of warm white light emitting diodes (WLEDs). Here, we report a promising and orderly‐layered candidate: Sr₄Al₁₄O₂₅:Mn⁴⁺ with CIE color coordinates (0.722, 0.278). It has higher luminescence efficiency particularly upon blue excitation and is much cheaper than the commercial red phosphor 3.5MgO·0.5MgF₂·GeO₂:Mn⁴⁺ (MMG:Mn⁴⁺). In sharp contrast to Eu²⁺‐doped (oxy)nitrides, the phosphor can be synthesized by a standard solid‐state reaction at 1200°C in air. The effects of flux boron content, environment, and preparation temperature, sintering dwelling time as well as Mn concentration have been systematically investigated for establishing the optimal synthesis conditions. The low temperature emission spectra reveal that there are at least three types of Mn⁴⁺ ions in Sr₄Al₁₄O₂₅:Mn⁴⁺ due to the substitution for the distorted octahedral Al³⁺ sites. The AlO₆ layers where Mn⁴⁺ prefers to reside are well separated from one another by AlO₄ tetrahedra in one dimension parallel to axis a. This scenario can efficiently isolate Mn⁴⁺ ions from local perturbations, thereby enabling the high efficiency of luminescence. The energy transfer rates and mechanism are discussed.     

Probing Site Symmetry Around Eu3+ in Nanocrystalline ThO2 Using Time Resolved Emission Spectroscopy

ThO₂:Eu³⁺ nanoparticles were synthesized at 300°C by combustion route using urea as a fuel and characterized by thermogravimetric/differential thermal analysis, X‐ray diffraction, transmission electron microscopy, and photoluminescence techniques. To investigate the effect of annealing temperature, as synthesized powder were heated further at 500°C, 700°C, and 900°C. It was observed that extent of asymmetry around Eu³⁺ at 700°C/900°C is very high as compared to as‐prepared or 500°C annealed sample. Based on the time resolved emission spectroscopic investigations, it was inferred that two different types of Eu³⁺ ions were present in the ThO₂ nanoparticles. In ThO₂ structure, Eu³⁺ ions occupy two sites; cubic (O_h) and noncubic (<C_2v) as can be confirmed from our emission studies. Short‐lived species T₁ (~1.3–3.4 ms) predominates at higher annealing temperature arises because of Eu³⁺ ions occupying noncubic (<C_2v) sites without inversion symmetry, whereas long‐lived species T₂ (~4.6–6.6 ms) can be ascribed to Eu³⁺ ions occupying cubic sites (O_h) with inversion symmetry.     

Preparation of strontium aluminate: Eu2+ and Dy3+ persistent luminescent materials based on recycling alum sludge

Eu²⁺ and Dy³⁺ doped strontium aluminate persistent luminescent materials are prepared by solid state reaction using alumina obtained from the alum sludge [1]. Three group compositions; Sr (NO₃)₂ with alumina (calcined at 1100 °C, ESA1), SrO with alumina (calcined at 1400 °C, ESA2) and Sr(NO₃)₂ with alumina (calcined at 1400 °C, ESA3) doped with Eu³⁺: Dy³⁺ ions in different molar ratios (1 Eu³⁺: 2Dy³⁺, 1.5 Eu³⁺: 1.5Dy³⁺, 2Eu³⁺:1Dy³⁺ and 2.5Eu³⁺: 0.5 Dy³⁺) were prepared. The samples were fired under different under active carbon at 1250 °C. Surface morphology, crystalline structure, Photoluminescence measurements and the decay characteristic were characterized by SEM, XRD, and the photoluminescence spectrometers, respectively. The effect of the firing temperature at 1250 °C was also determined by apparent porosity and bulk density measurements. The results indicated that the main composition of the samples fired under active carbon powder was strontium aluminate with a very small amount of secondary phases. The results showed that the samples fired under active carbon had good phosphorescence properties and good decay time. A broad band UV-excited luminescence of the SrAl₂O₄:Eu²⁺, Dy³⁺ phosphorescent pigments was observed at λ_max = 517 nm due to transitions from 4f⁶, 5d¹ to 4f⁷ configuration of the emission center (Eu²⁺ ions). Photoluminescence spectra for ESA1 group show higher intensity than that of ESA2 and ESA3 groups. The difference in the behavior of the photoluminescence spectra for the three groups can be attributed to (i) different synthesis methods and (ii) the presence of different mixed phases (major SrAl₂O₄ and secondary phases).     

Optimized photoluminescence of red phosphor Na2SnF6:Mn4+ as red phosphor in the application in “warm” white LEDs

The Mn⁴⁺ activated fluostannate Na₂SnF₆ red phosphor was synthesized from starting materials metallic tin shots, NaF, and K₂MnF₆ in HF solution at room temperature by a two‐step method. The formation mechanism responsible for preparing Na₂SnF₆:Mn⁴⁺ (NSF:Mn) has been investigated. The influences of synthetic parameters: such as concentrations of HF and K₂MnF₆ in reaction system, reaction time, and temperature on crystallinity, microstructure, and luminescence intensity of NSF:Mn have been investigated based on detailed experimental results. The actual doping concentration of Mn⁴⁺ in the NSF:Mn host lattice is less than 0.12 mol%. The most of K₂MnF₆ is decomposed in HF solution especially in hydrothermal system at elevated temperatures. The color of the as‐prepared NSF:Mn samples changes from orange to white when the temperature is higher than 120°C, which indicates the lower concentration of luminescence centers in the crystals. A series of “warm” white light‐emitting diodes with color rendering index (CRI) higher than 88 and correlated color temperatures between 3146 and 5172 K were obtained by encapsulating the as‐prepared red phosphors NSF:Mn with yellow one Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) on 450 nm blue InGaN chips. The advantage of the synthetic strategy to obtain NSF:Mn can be extended to developing Mn⁴⁺‐doped red phosphors from low‐costing metals at room temperature for large‐scale industrial applications.     

Synthesis of a novel inorganic cation exchanger based on molybdate: Applications for removal of Pb2+, Fe3+ and Mn2+ ions from polluted water

A novel manganese phosphomolybdate exchanger was synthesized, dried at different temperatures, and evaluated for the elimination of lead, iron, and manganese ions from aqueous solutions. The chemical structure of the cation exchanger was established using Fourier-transform infrared, scanning electron microscopy, Thermo gravimetric analysis/ Differential thermal analysis, and X-ray diffraction. The adsorption performance of the heavy metals Pb²⁺, Fe³⁺, and Mn²⁺ toward the synthesized material has been studied. The obtained outcomes show that the selectivity of the cationic exchanger was descending in this order, Pb²⁺ > Fe³⁺ > Mn²⁺. The highest adsorption capacity was shown to be decreased as drying temperature of the exchanger increases from 50°C to 800°C.     

Phase Transformation in Ca3(PO4)2:Eu2+ via the Controlled Quenching and Increased Eu2+ Content: Identification of New Cyan‐Emitting α‐Ca3(PO4)2:Eu2+ Phosphor

A case of phosphor is reported where the cooling rate parameter significantly influences the luminescence property. By quenching the sample after the high‐temperature solid‐state reaction at 1250°C, we successfully prepared the Eu²⁺‐doped α form Ca₃(PO₄)₂ (α‐TCP:Eu²⁺) as a new kind of bright cyan‐emitting phosphor. The unusual emission color variation (from cyan to blue) depends on the cooling rate after sintering and Eu²⁺ doping level as it was observed in the TCP‐based phosphors. By the Rietveld analysis, it is revealed that the cyan‐ and blue‐emitting phosphors are two different TCP forms crystallizing in the monoclinic (space group P2₁/a, α‐TCP) and the rhombohedral structure (space group R3c, β‐TCP), respectively. Upon 365 nm UV light excitation, α‐TCP:Eu²⁺ exhibits an asymmetric broad‐band cyan emission peaking at 480 nm, while β‐TCP:Eu²⁺ displays a relatively narrow‐band blue emission peaking at 416 nm. The Eu²⁺‐doping in Ca₃(PO₄)₂ shifts the upper temperature limit of the stable structural range of β form from 1125°C to ≥1250°C. Moreover, the crystal structures of α/β‐TCP:Eu²⁺ were compared in the aspects of compactness and cation site sets. The emission thermal stability of α/β‐TCP:Eu²⁺ was comparatively characterized and the difference was related to the specific host structural features.     

Preparation and Luminescence Properties of Eu2+ and Mn2+ Coactivated Tricalcium Phosphate Phosphors

Eu²⁺ and Mn²⁺ coactivated β–Ca₃(PO₄)₂ (TCP) phosphors have been prepared by high‐temperature solid‐state reaction. The site occupation and photoluminescence properties of Eu²⁺ and Mn²⁺ have been identified and discussed in detail. The energy transfer from Eu²⁺ to Mn²⁺ in TCP: Eu²⁺, Mn²⁺ phosphors has been validated and demonstrated to be a resonant type via a dipole‐quadrupole mechanism, and the critical distance (R_C) calculated by concentration quenching method is 21.76 Å. A color‐tunable emission from violet‐blue to red in TCP: Eu²⁺, Mn²⁺ phosphors can be realized via the energy transfer from Eu²⁺ to Mn²⁺ ions.     

Catalytic combustion of SOFC stack flue gas over CuO and Mn2O3 supported by La0.8Sr0.2Mn0.67Cu0.33O3 perovskite

An efficient oxidation catalyst was developed to increase the combustion efficiency of unreacted CO, H₂, and CH₄ in flue gas of solid oxide fuel cell (SOFC) stack. Amorphous Cu‐Mn oxide catalyst (CuMnLa/Alumina) showed high catalytic activity, but significant degradation occurred due to phase transition to spinel structure at high temperatures (T > 650°C). La_0.8Sr_0.2Mn_0.67Cu_0.33O₃ perovskite (LSMC(p)) supported CuO or Mn₂O₃ exhibited improved thermal stability than CuMnLa/Alumina catalyst. Especially in case of 50Mn/LSMC(p), after the catalyst was exposed to 800°C for 24 h, T₅₀ of CO, H₂ and CH₄ was achieved at 170, 230, and 600°C, respectively. This result is much lower than that of CuMnLa/Alumina, which was exposed to the same condition. The high combustion efficiency is due to retention of the Cu²⁺‐Mn³⁺ redox couple, and supply of lattice oxygen from LSMC(p), especially at high temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 940–949, 2018     

Self-reduction and enhanced luminescence in transparent Mn2+-doped mullite glass-ceramics derived from EMT-type zeolite

Mn²⁺ activated glass-ceramic (GC) has received tremendous attention in the exploration of luminescent materials for solid-state lighting due to the high stability, broad red emission, and low toxicity. However, the doped Mn²⁺ ions still suffer from the oxidation and uncontrollable ions migration during the melting process of conventional preparation techniques, which is detrimental to the luminescence performance. Herein, transparent Mn²⁺-doped mullite GCs have been prepared at low temperature (∼850°C) via the spark plasma sintering of EMT-type zeolite. The GC samples show typical red emission peaking at 620 nm that can be assigned to spin-forbidden ⁴T₁(G)→⁶A₁(S) transition of Mn²⁺ located in the octahedral coordination site of the host. Owing to the charge compensation mechanism and produced oxygen vacancies, the self-reduction of Mn³⁺ to Mn²⁺ ions is realized and the oxidization is inhibited. The mullite nanocrystals acted as additional scattering centers introduce Rayleigh scattering to enhance the emission intensity. Moreover, benefitted from the established mullite nanocrystals network, the Mn²⁺-doped GCs exhibit improved thermal conductivity up to 1.79 W K⁻¹ m⁻¹ and more excellent mechanical properties than conventional GCs, simultaneously.     

Diametral strength testing of hydroxyapatites doped with yttrium and fluoride

Abstract

Abstract

This study aimed to investigate the diametral strength testing of hydroxyapatite (HA) doped with Y and fluoride with different compositions. Hydroxyapatites were synthesised by precipitation method and sintered at 900, 1100 and 1300°C for 1?h. High amounts of doping caused a decrease in relative densities of HAs. Higher sintering temperatures helped in increasing the relative densities. No second phases were observed by X-ray diffraction spectra of 2·5?mol.-%Y and 2·5?mol.-%F doped HA after the sintering at all temperatures. Trace amounts of β-tricalcium phosphate was found in 7·5?mol.-%Y and 2·5?mol.-%F doped HA sintered at 1100 and 1300°C. Diametral strength of doped HAs mostly enhanced with the addition of Y³⁺ and F^?. 2·5YFHA sintered at 1300°C had the highest diametral strength of 11·6?MPa with a relative density of 94·3% of theoretical density.     

Efficient red and broadband near-infrared luminescence in Mn2+/Yb3+-doped phosphate phosphor

In this work, we report a novel phosphor LSPO:Mn²⁺ that exhibits red emission at about 616 nm and pleasant broad near-infrared (NIR) emission at about 800 nm with a full width at half maximum (fwhm) of 112 nm. The structure and spectra show that the doped manganese ions occupy two kinds of Sc sites forming Mn1 and Mn2 emission centers, which are responsible for red and NIR emission, respectively. The XPS and low-temperature fluorescence spectra reveal that both red and NIR emissions come from the Mn²⁺ ions. Besides, NIR luminescence is improved by doping Yb³⁺ in LSPO:Mn²⁺, leading to the broadened NIR emission range (700-1100 nm) and enhanced luminescent thermal stability. Our results suggest that the prepared LSPO:Mn²⁺ and LSPO:Mn²⁺,Yb³⁺ phosphors offer the potential applications as red and NIR components in phosphor-converted white-light-emitting diodes (pc-WLED) and broadband NIR pc-LED. Meanwhile, this work provides a new way to design novel broadband NIR phosphors.     

Expanded and Enhanced Deep‐UV Excitations of Mn2+‐Doped Phosphate Glasses Sensitized by Gd3+ Ions

Mn²⁺‐doped phosphate glasses sensitized by Gd³⁺ ions are investigated. Enhanced photoluminescence (PL) properties of the samples are found with the excitations expanding toward the deep‐UV part of the spectrum. PL emission and excitation spectra correlated with the lifetime data consistently present evidences of the enhanced Mn²⁺ emission in association with the energy transfer from Gd³⁺ ions. In particular, the Gd³⁺ codoping benefits greatly the energy harvesting of Mn²⁺ ions, resulting in the enhanced and tunable excitations of Mn²⁺ ions which expand toward the deep‐UV part of the spectrum at 273 and 311 nm, respectively. Thus by Gd³⁺ sensitizing, the excitation source of the Mn²⁺ emission has covered the broad range of the spectrum from the original blue and near‐UVA to the deep‐UVB and UVC together with the enhanced emission in the green‐to‐red spectral region. The possible energy‐transfer mechanisms involved are discussed.     

Facilitated Transport of Cadmium Ions from Hydrochloric Acid Solutions through a Liquid Membrane Containing Dicyclohexyl‐18‐Crown‐6 as Extractant‐Carrier

Abstract

The transport of cadmium ions from hydrochloric acid solutions across a bulk liquid membrane by using dicyclohexyl‐18‐crown‐6 (DC18C6) dissolved in dichloromethane has been studied at 25°C. The effect of the fundamental parameters influencing the transport, e.g., hydrochloric acid concentration in the feed phase, DC18C6 concentration and the type of diluent used in the membrane and time of transport have been investigated. The transported amount of the cadmium ions (initial concentration 0.001 M) from a 6 M hydrochloric acid solution across a dichloromethane solution of DC18C6 (0.05 M) into distilled water (receiving phase) was found to be 98.3 (±1.8) percent after 6 h. The selectivity and efficiency of the method toward cadmium ions were tested by performing the competitive transport experiments on the mixtures containing Cd²⁺, Ni²⁺, Mn²⁺, Co²⁺, Zn²⁺, Pb²⁺, and Fe²⁺ ions. The best selectivity was found for the recovery of the cadmium ions from its mixture with Ni²⁺, Mn²⁺, Co²⁺, and Pb²⁺ ions. Thus, the method can be proposed for the application in cadmium recovery from the sources containing these ions such as spent rechargeable nickel‐cadmium batteries.     

Role of potassium in the aerobic oxidation of aromatic alcohols over K+-promoted Mn/C catalysts

The aerobic oxidation of aromatic alcohol on alkali metal promoted Mn/C catalysts has been investigated. A dramatic improvement of the oxidation activity can be observed when the Mn/C catalyst is modified with potassium ions. Characterizations of Raman and X-ray absorption fine structure (XAFS) evidence that potassium ions induce a large local distortion to Mn–O octahedrons in supported manganese oxides with coexistence of Mn²⁺ and Mn³⁺, which has been suggested to be a vital factor to enhance the activation of O₂ for the oxidation of benzylic alcohol.     

Effect of Mn2+ doping on the lattice and the microwave dielectric properties of MgTa2O6 ceramics

A series of Mn²⁺-doped Mg_1-xMn_xTa₂O₆ (x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ceramics were synthesized by solid-state reaction method. The influence of introducing Mn–O bonds as a partial replacement for Mg–O bonds on the lattice and microwave dielectric properties was systematically investigated. XRD and Rietveld refinement confirm that Mn²⁺ occupies the 2a Wyckoff position and forms a pure trirutile phase. Moreover, based on the chemical bond theory, the dielectric constant is mainly affected by the ionicity of the Ta–O bond. The lattice and dielectric properties remain relatively stable with Mn²⁺ doping below 0.1, but excessive Mn²⁺ doping leads to pronounced distortion of the lattice, which is not beneficial for lattice stability and microwave dielectric properties. Introducing an appropriate amount of Mn–O bonds with high bond dissociation energy facilitates MgO6 octahedron stability, which improves the thermal stability of the lattice. Accordingly, the microwave dielectric properties for 0.06 Mn²⁺-doped MgTa₂O₆ ceramics were determined: ε_r = 28, Q × f = 105,000 GHz (at 7.5 GHz), τ_f = 19.5 ppm/^°C.