Lumine scence of Ce3+ and Tb3+ in M3(PO4)2 (M = Sr,Ba)

The luminescence properties of Ce³⁺- and Tb³⁺-activated M₃(PO₄)₂ (M = Sr,Ba) are reported. It is shown that only a small part (⩽ 0.3%) of the M2+ ions can be replaced by Ln³⁺ ions. At higher concentrations a second phase, M₃Ln(PO₄)₃, is formed. The luminescence properties are due to these two different phases.     

钙钛矿型复合氧化物MZrO3（M=Ba,Sr）的水热合成

利用水热晶化法对ＢａＺｒＯ３和ＳｒＺｒＯ３的制备进行了研究，对不同水热条件下的产物进行了结构表征，并探讨了最佳合成条件，结果表明，１５０℃，晶化１ｄ为最佳水热晶化条件，介质的适宜碱度为ＫＯＨ／Ｚｒ≈４。在此条件下，可获得３－７μｍＢａＺｒＯ３和５－１５μｍＳｒＺｒＯ３的多晶粉末。     

白光LED用红色荧光粉MMoO4:Eu3+（M=Ca,Sr,Ba）的制备与表征

采用高温固相法制备了红色荧光粉MMoO4:Eu3+(M=Ca,Sr,Ba),用XRD和荧光分光光度计对其物相及发光性能进行表征和研究。结果表明,在800℃时可得到MMoO4(M=Ca,Sr,Ba)物相结构。分别以395nm的近紫外光和465nm的可见光激发样品,MMoO4:Eu3+(M=Ca,Sr,Ba)荧光粉发红光,对应于Eu3+的4f-4f跃迁,其中以616nm发光最强。荧光粉在395nm和465nm的吸收分别与紫外光和蓝光LED芯片相匹配。     

Ce to Tb energy transfer in alkaline earth (Ba, Sr or Ca) sulphate phosphors

Energy transfer between Ce³⁺ and Tb³⁺ dopants in alkaline earth (Ba, Sr or Ca) sulphate phosphors is investigated. Among these three phosphors, CaSO₄:Ce³⁺,Tb³⁺ showed maximum Tb³⁺ green emission on excitation with UV light. Photoluminescence measurements reveal that the emission intensity from CaSO₄:Ce³⁺,Tb³⁺ is comparable with that of the commercial green lamp phosphor Ce_0.65Tb_0.35MgAl₁₁O₁₉. Optimum concentrations of dopants in CaSO₄:Ce³⁺,Tb³⁺ are 0.2 mol% each and the optimum sintering treatment following re-crystallisation is 600 °C for 1 h duration. The effect of charge compensator in all the three phosphors is also studied.     

MSnO_3和MSn_（0．5）Zr_（0．5）O_3（M＝Sr，Ba）的水热合

本文利用水热合成方法对ＭＳｎＯ３和ＭＳｎ（０．５）Ｚｒ（０．５）Ｏ３（Ｍ＝Ｓｒ，Ｂａ）的合成进行了研究，并采用ＸＲＤ、ＳＥＭ和ＩＣＰ等方法对产物进行了表征，结果表明：在Ｍ（ＯＨ）２－ＳｎＯ２（或ＳｎＯ２＋ＺｒＯ２）－ＫＯＨ体系中，当ＫＯＨ／Ｓｎ和ＫＯＨ／（Ｓｎ＋Ｚｒ）≥３０时，２６０℃下晶化５～７天，可获得ＭＳｎＯ３和ＭＳｎ（０．５）Ｚｒ（０．５）Ｏ３纯相，在Ｍ（ＯＨ）２－（ＳｎＯ２＋ＺｒＯ２）－ＫＯＨ－Ｈ２Ｏ体系中，可通过控制介质碱度来获得ＭＳｎＯ３＋ＭＺｒＯ３混合物和ＭＳｎ（０．５）Ｚｒ（０．５）Ｏ３，并根据合成规律初步探讨了反应过程．     

Solution synthesis of crystallized AMO4 (A=Ba, Sr, Ca; M=W, Mo) film at room temperature

A well-crystallized AMO₄ (A=Ba, Ca, Sr; M=W, Mo) films have been prepared at room temperature through a simple solution reaction in respective alkaline solution at higher pH ranging from 12–14. Adopting the corrosion principle for oxidation of metal substrate, these double oxide films were carried out in presence of chemical driving force without any special apparatus or devices. Hydrogen peroxide was used to enhance the dissolution rate of metal substrates. The driving force for the film formation and growth were high concentration of A²⁺, MO₄²⁻ ions with high pH conditions. Average grain sizes of 8–10 μm with bipyramidal shaped particle were grown to the thickness of about 10–14 μm after 3–6 hours treatment. The crystallization of AMO₄ was characterized by three-dimensional nucleation. This work demonstrates the possibility of fabrication of functional ceramic films directly from the aqueous solution in a single step by solution reactions.     

Physicochemical properties of La(Ba,M)CuFeO5+δ (M = Sr, Ca, Mg) solid solutions

The crystal structure of LaBa_1?x M_xCuFeO_5+δ (M = Sr, Ca, Mg; 0 < x ≤ 0.5) solid solutions has been studied by x-ray diffraction and IR absorption spectroscopy, and their thermal stability, thermal expansion, and electrical conductivity have been determined in air between 290 and 1270 K. The structure of LaBa_1?x Sr_xCuFeO_5+δ has been shown to change from cubic to tetragonal at x ? 0.4?0.45, whereas the LaBa_1?x M_xCuFeO_5+δ (M = Ca, Mg) solid solutions have a cubic structure up to x = 0.5. The composition dependences of structural parameters and physicochemical properties for LaBa_1?x Sr_xCuFeO_5+δ show anomalies at x = 0.25, which suggests ordering of the La³⁺, Ba²⁺, and Sr²⁺ cations in the structure of La(Ba,Sr)CuFeO_5+δ, leading to the formation of a new chemical compound, LaBa_3/4Sr_1/4CuFeO_5+δ.     

SrWO4:Tb3+ nanoparticles: synthesis,characterization, and luminescence

Nanoparticles of SrWO₄ doped with Tb³⁺ were synthesized in ethylene glycol, Dimethyl sulfoxide, and water. X-ray powder diffractions show that the nanoparticles synthesized in all these solvents have a pure tetragonal scheelite structure without the presence of deleterious phases. Scanning electron microscopy images show that nanoparticles are in the range of 15–25 nm with an inhomogeneous nature. The emission spectra of SrWO₄:xTb³⁺ nanoparticles show the characteristic green emission (545 nm) of Tb³⁺ ions corresponding to ⁵D₄ → ⁷F₅ transition due to efficient charge transfer from WO₄ ^2? to Tb³⁺ ions, when they are excited at 254 nm. Other emissions can be observed due to ⁵D₄ → ⁷F_{6, 4, 3} transitions. The optimum concentration of Tb³⁺ ions for the highest luminescence was found to be 10 mol%. The luminescence intensity of the samples prepared in ethylene glycol is higher than that in Dimethyl sulfoxide and water. The excellent luminescence properties of SrWO₄:Tb³⁺ phosphor makes it as a potential green phosphor.     

Soft-Mode Behavior in Ternary Silicides MAlSi (M=Ca, Sr, Ba)

We present a combined experimental and theoretical investigation of the lattice dynamics and electron–phonon coupling of the ternary silicides MAlSi (M = Ca, Sr, Ba). Temperature dependent inelastic neutron-scattering measurements of the generalized phonon density-of-states provide evidence for a soft-mode behavior for CaAlSi which is absent for the other two compounds. Density-functional-based calculations of phonon spectra and electron–phonon coupling support this interpretation and identify the soft mode as strong coupling out-of-plane Al vibrations, in agreement with previous theoretical work. Observed differences in superconducting properties, in particular in T _c , among the investigated compounds can be explained by the presence of the soft mode.     

Mechanochemically assisted room temperature solid state metathesis reaction for the synthesis of MMoO4 (M = Ca, Sr and Ba)

This communication reports a novel mechanochemically assisted room temperature solid state metathesis reaction for the synthesis of submicron-size alkaline-earth molybdates crystallizing in a tetragonal Scheelite structure. The solids were characterized by powder XRD, FTIR, TGA, DTA, SEM, EDAX and TEM to ascertain their composition, phase homogeneity and morphology.     

Phase evolution and microstructural development in sol-gel derived MSnO3 (M = Ca, Sr and Ba)

Alkaline-earth stannates having the general chemical formula MSnO₃ (M = Ca, Sr and Ba) have been projected as potential electronic ceramics. In view of the information gaps in the reported research, a vigorous and systematic investigation on these exotic materials has been carried out. In this communication, the synthesis of CaSnO₃, SrSnO₃ and BaSnO₃ via sol-gel technique is reported. Infrared spectroscopy and X-ray analyses of various gel samples with different thermal history helped in identifying the reaction pathways and the stage where amorphous gel to crystalline phase transition occurred. Grains of submicron size with narrow size distribution and spherical morphology, were the most noticeable characteristics of sintered calcium metastannate derived by sol-gel method. In the case of barium analogue, a fascinating sugar cube structure (akin to that observed in solid-state reaction and the self-heat-sustained reaction derived samples) having improved density characteristics evolved at low sintering temperatures. This gradually transformed into a more familiar spherical granular motif with improved density characteristics as the sintering profiles were varied from 1200 °C/24 h to 1500 °C/2 h. This seems to be an inherent feature of this system, irrespective of the method of synthesis.     

Hydrothermal synthesis and luminescent properties of (La,Gd)PO4:Tb phosphors under VUV excitation

Tb doped orthophosphate phosphors with monoclinic system were successfully prepared by mild hydrothermal reaction at 240 °C. The emission characteristics of phosphors (La,Gd)PO₄:Tb under 147 nm excitation were studied. The quenching concentration of Tb in LaPO₄ is 15 mol% and when Gd is co-doped into the matrix the Tb emission at 543 nm is improved further. The emission intensity of the optimal composition of La_0.55Gd_0.3Tb_0.15PO₄ is comparable with that of commercial Zn₂SiO₄:Mn phosphor. The study of its optical properties suggests that it is a potential candidate for plasma display panels (PDPs) application.     

Color tunable and thermally stable luminescence of Tb3+ doped Li4SrCa(SiO4)2 phosphors

Tb³⁺ ions activated Li₄SrCa(SiO₄)₂ phosphors were synthesized using a solid state reaction method. The phase impurity was checked by XRD. The photoluminescence (PL) excitation spectrum, emission spectra at room and high temperature, decay curves of samples with different Tb³⁺ ions concentration were studied in detail. Cross-relaxation and the Inokuti–Hirayama model were used to analyze the experimental results. Li₄SrCa(SiO₄)₂:xTb³⁺ are thermally stable and color tunable phosphors.     

Luminescent properties of Eu3+ activated MLa2(MoO4)4 based (M = Ba,Sr and Ca) novel red-emitting phosphors

Eu³⁺-activated novel red phosphors, MLa₂(MoO₄)₄ (M = Ba, Sr and Ca) were synthesized by the conventional solid state method. The excitation and emission spectra indicate that these phosphors can be effectively excited by UV (395 nm) and blue (466 nm) light, and exhibit a satisfactory red performance at 614 nm. Upon excitation with a 466 nm light, our synthesized phosphors have stronger emission intensity than the sulfide red phosphors used in white LEDs. Due to high emission intensity and a good excitation profile, the Eu³⁺-doped CaLa₂(MoO₄)₄ phosphor may be a promising candidate in solid-state lighting applications.     

A structural study on MFCl (M=Ca, Sr, Ba) and BaFX (X=Br, I)

Here we present the electronic band structure calculations of CaFCl, SrFCl, BaFCl, BaFBr and BaFI performed using tight binding linear muffin-tin orbital method. The calculated ground state properties namely the lattice parameters, bulk moduli and the pressure-volume relations were found to be in good agreement with the experimental values. The electronic band structure of these compounds were calculated at ambient as well as in the high pressure region. The band gap values of these insulating systems were calculated and compared with available experimental values. At high pressure these compounds exhibit the interesting phenomenon of band overlap metallization.     

MF2(M=Mg,Ca,Zn,Sr,Ba)对掺Yb3+磷酸盐玻璃性质的影响

熔制了60P₂O₅·6Al₂O₃·(33-x)BaO·xBaF₂·1Yb₂O₃(x=0,3,6,9)和60P₂O₅·6Al₂O₃·27BaO·6MF₂·1Yb₂O₃(M=Mg、Ca、Sr、Zn、Ba)(分子分数)玻璃,测试了其折射率、密度、转变温度、析晶温度、熔点温度、红外光谱和紫外吸收光谱,讨论了二价氟化物MF₂(M=Mg、Ca、Sr、Zn、Ba)对磷酸盐玻璃热稳定性及内部结构的影响,测试了Yb³⁺离子的吸收光谱、荧光光谱、荧光寿命,计算了光谱参数,讨论了MF₂对Yb³⁺磷酸盐玻璃光谱性质的影响,结果表明二价金属氟化物是作为网络外体进入到磷酸盐玻璃结构中,并没有改变磷酸盐玻璃内部的[PO₄]链状结构,二价金属氟化物还有助于提高Yb³⁺离子的受激发射截面,和自发辐射几率,荧光半高宽。