[en] The crystalline grain growth and the dielectric and the piezoelectric properties of Li- and Ta-modified (Na_0.05K_0.47Li_0.03)(Nb_0.8Ta_0.2)O₃ (NKLNT) ceramics were investigated for different sintering temperatures. The sintering temperature affected the grain growth, density, dielectric constant, and piezoelectric coefficient. The grain growth, density, dielectric constant, and piezoelectric coefficient were enhanced when the optimum sintering temperature T_s = 1080 °C was adopted. The sintering temperature impacts high performance because of a narrow temperature window in which the piezoelectric properties can be controlled. We investigated several aspects, including the optimum sintering, grain morphologies, dielectric behavior, and piezoelectric properties.

[en] Lanthanide(Ln)doped materials find potential applications in the fields of lasers, optical amplifiers, phosphors, display devices, etc., due to their characteristic energy level schemes. These materials found wide useful in the development of plasma display panels(PDP), field emission displays(FED)and electro luminescent panel applications. Recently, REPO_4(RE=Y, La, Gd, Lu)materials have attracted much attention in PDP applications due to their high thermal and chemical stability as well as high luminescence efficiency under VUV excitation. Tricolor inorganic luminescence materials are used in PDP to emit red, green and blue light. PDP phosphors emit visible light under VUV excitation. The VUV pump photon is absorbed by the host lattice and color purity are most essential. It is thus necessary either to further improve the luminescence properties, or to develop new phosphors. It is possible to tune the intensity of red emission by modifying the neighboring network design around Eu"3"+ ions on introducing other atoms such as Ca, Sr, Ba, Zn, Al, Li, Sc, Bi, La, Gd, etc., into the ortho phosphate host lattice. The prepared samples are characterized by XRD, SEM, photoluminescence excitation, photoluminescence emission and lifetime measurements. The results are also compared with those of earlier reported works

[en] Over the past few years, much attention has been paid to the synthesis and development of luminescence properties, of various lanthanide (Ln)doped materials that are useful for plasma display panels (PDPs). In order to display full colors in PDPs, red, green and blue phosphors are required. The PDP phosphors emit visible light under VUV excitation. The VUV pump photon is absorbed by the host lattice and the absorbed energy is transferred to the activator. Since the red emission, which comes from the "5"D"0"→"7"F"2"transition, is hypersensitive to the lattice symmetry of the host crystal and will be relatively strong if the symmetry of the crystal is low, it is possible to tune the intensity of red emission by modifying the neighboring network design around Eu"3+"ions on introducing other atoms such as Ca, Sr, Ba, Zn, Al, Li, Sc, Bi, La, Gd, etc., into the ortho borate host lattice. Incorporation of these metal atoms into the host lattice of YBO"3"distorts the lattice to modify the energy absorption and transfer behaviors, resulting in an increased emission intensity. In this work, we have prepared Y"(0.95-X)Eu"0.05"BO"3":Al"3+""(X)"(x=0, 0.05, 0.10, 0.15 and 0.20)phosphors by solid state reaction method by using the high purity chemicals of Y"2"O"3", H"3"BO"3", Eu"2"O"3"and Al"2"O"3"to study the effect of concentration of Al"3+"ions on the luminescence properties of Eu"3+"ions in YBO"3"phosphor. The prepared samples are characterized by XRD, SEM, photoluminescence excitation, photoluminescence emission and lifetime measurements. The results are also compared with those of earlier reported works

[en] Eu³⁺ or Sm³⁺ singly-doped and Eu³⁺ and Sm³⁺ co-doped KZnGd(PO₄)₂ phosphors were synthesized by using a conventional solid state reaction method at 750 .deg. C. The emission spectra of KZnGd_1-x(PO₄)₂:Eu³⁺_x with λ_ex = 395 nm and KZnGd_1-y(PO₄)₂:Sm³⁺_y with λ_ex = 403 nm phosphors showed intense ⁵D₀ → ⁷F₁, ⁴G_5/2 → ⁶H_7/2 emission transitions at 595 nm and 599 nm, respectively. The optimum relative intensity of the KZnGd_1-x-y(PO₄)₂:Eu³⁺_x , Sm³⁺_y phosphor was obtained for the doping concentrations of (x = 0.09, y = 0.01). In addition, the temperature dependent luminescence intensity of the synthesized phosphors was investigated and the thermal stability of the KZnGd(PO₄)₂:Eu³⁺ phosphor was found to be higher than that of standard YAG:Ce³⁺ and KZnGd_1-x-y(PO₄)₂:Eu³⁺_x Sm³⁺_y under near ultra-violet (NUV) light emitting diode excitation (LED). Therefore, we suggest that Eu³⁺ or Sm³⁺ singly-doped and Eu³⁺ and Sm³⁺ co-doped KZnGd(PO₄)₂ phosphors should be efficient for different red-color-emitting display device applications and NUV-LED-based white-light-emitting diodes.

[en] Spectroscopic properties of Sm³⁺ (1 mol%) ions in 49 PbO-30 GeO₂-20 TeO₂ glass have been characterized through optical absorption and temperature dependent fluorescence. The spectroscopic parameters such as oscillator strengths (f), Judd-Ofelt (J-O) intensity parameters (Ω_λ), spontaneous emission probability (A_R), branching ratios (β_R) and radiative lifetimes (τ_R) of various excited levels have been determined from the absorption spectrum by using J-O analysis. From the fluorescence spectra, four emission transitions have been observed from the ⁴ G_5/2 state to the lower lying states ⁶H_5/2, ⁶H_7/2, ⁶H_9/2 and ⁶H_11/2 upon exciting the sample with a 488 nm line of an argon ion laser. The stimulated emission cross-sections (σ_e) and branching ratios (β_meas) were estimated from the emission spectra for all emission transitions and decay curve analysis for the ⁴G_5/2 level has also been carried out for different concentrations. Based on these results, the utility of Sm³⁺ doped lead-germanate-tellurite glasses as laser active materials in the visible region is discussed

[en] LaVO₄ phosphors were synthesized by using a solid state reaction, and were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The XRD patterns of the Li-doped LaVO₄:Eu³⁺ powder phosphors revealed a mixture of tetragonal and monoclinic phases. The tetragonal phase of the LaVO₄:Eu³⁺ phosphor showed a higher PL intensity than the monoclinic one, despite the presence of both monoclinic and tetragonal structures. The Li-doped LaVO₄:Eu³⁺ powder phosphors absorbed strongly at 396 nm and exhibited strong red emission at approximately 619.5 nm due to the ⁵D₀ → ⁷F₂ transition. The incorporation of Li⁺ ions into the LaVO₄:Eu³⁺ powder can lead to a remarkable increase in photoluminescence. The enhanced luminescence is attributed to the incorporation of Li⁺ ions that may act as a sensitizers for effective energy transfer. This phosphor has promising applications in near-UV light-emitting diodes(LEDs).

[en] Sm³⁺-doped Li₂O-SrO-B₂O₃ glass sample was prepared by the conventional melt quenching method in air atmosphere. Sm²⁺ ions in this borate glass were obtained by x-ray irradiation reduction method. The as-prepared and x-ray-irradiated samples were investigated by photoluminescence spectrum and decay curve measurements. The dependence of Sm²⁺ luminescence intensity on the x-ray irradiation time was investigated. It is found that the conversion of Sm³⁺→Sm²⁺ after x-ray irradiation is efficient in this borate glass. Photostability of Sm²⁺ ions was evaluated by the photobleaching method. Furthermore, the induced optical absorption spectrum measurement after x-ray irradiation was performed. Thermoluminescence above room temperature was also studied after x-ray irradiation. The different kinds of defect structures and the reduction mechanism of Sm²⁺ ions in this borate glass were discussed. The microstructure of Sm ions in the Li₂O-SrO-B₂O₃ glass was suggested. The proposed microstructure would be helpful to understand the reduction mechanism of Sm²⁺ ion in borate glasses

[en] The synthesis of narrowly dispersed nanocrystalline TiO₂ was investigated with a surfactant aided solvothermal synthetic method in toluene solutions. When a sufficient amount of titanium isopropoxide, Ti[OCH(CH₃)₂]₄ (TIP), was added to the solution, the shapes of TiO₂ nanoparticles changed from spheres to rods. The aggregated microstructures of the nano-sized TiO₂ in systems of spheres, rods, and mixtures of spheres and rods was studied using TEM. The morphological shape of the aggregation was described in terms of the fractal dimensions. We used a box-counting method to get the fractal dimension of these systems. The fitted fractal dimensions for spheres, sphere/rod mixtures, and rods are D = 1.54, D = 1.81, and D = 1.89, respectively. The fractal dimension changed from 1.54 to 1.9 with the TIP/toluene ratio, indicating that the growth mechanism for aggregations showed different behaviors.

[en] Dysprosium doped ZnO-B₂O₃-P₂O₅ (ZBP) glasses were prepared by a conventional melt quenching technique in order to study the luminescent properties and their utility for white light emitting diodes (LEDs). X-ray diffraction spectra revealed the amorphous nature of the glass sample. The present glasses were characterized by infrared and Raman spectra to evaluate the vibrational features of the samples. The emission and excitation spectra were reported for the ZBP glasses. Strong blue (484 nm) and yellow (574 nm) emission bands were observed upon various excitations. These two emissions correspond to the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ions, respectively. Combination of these blue and yellow bands gives white light to the naked eye. First time, it was found that ZnO-B₂O₃-P₂O₅ glasses efficiently emit white light under 400 and 454 nm excitations, which are nearly match with the emissions of commercial GaN blue LEDs and InGaN LED, respectively. CIE chromaticity coordinates also calculated for Dy³⁺: ZBP glasses to evaluate the white light emission.

[en] A series of red phosphors Ca_1-xZrSi₂O₇ : Eu_x (x = 0.5,1,5,10,12 mol%) were prepared by a solid-state reaction technique at various temperatures and their structural and optical properties were investigated. The x-ray diffraction profiles showed that all peaks could be attributed to the monoclinic phase CaZrSi₂O₇ doped with Eu³⁺. SEM, FTIR, TG and DTA profiles have also been characterized to explore their structural properties. The luminescence properties of these resulting phosphors have been characterized by photoluminescence spectra. The host matrix itself has shown a strong blue emission which has its maximum intensity at 470 nm. The excitation spectra of CaZrSi₂O₇ : Eu³⁺ revealed two excitation bands at 395 and 464 nm which correspond to the sharp ⁷F₀-⁵L₆ and ⁷F₀-⁵D₂ transitions of Eu³⁺ and matches well with the two popular emissions from n-UV/blue GaN-based LEDs. The prominent red emission was obtained at 615 nm by the excitation transitions ⁵L₆, ⁵D₂ of Eu³⁺ through the non-radiative energy transfer process from the host to the Eu³⁺ ion. The effects of charge compensation by monovalent ions on the luminescence behaviour of a red emitting phosphor CaZrSi₂O₇ : Eu³⁺ were investigated. The high colour saturation and the low thermal quenching effect of these phosphors make it a potential red component for white light emitting diodes (w-LEDs).