Search

The color-tunable up-conversion (UC) emission and infrared photoluminescence and dielectric relaxation of Er3+/Yb3+ co-doped Bi2Ti2O7 pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase structure of Bi2Ti2O7 can be stabilized by Er3+/Yb3+ co-doping. Intense color-tunable UC emission and infrared photoluminescence can be detected on the thin films excited by a 980 nm diode laser. Two UC emission bands centered at 548 and 660 nm in the spectra can be assigned to 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. A Stokes infrared emission centered at 1530 nm is due to 4I13/2 → 4I15/2 transition of Er3+ ions. The dependence of UC emission intensity on pumping power indicates that the UC emission of the thin films is a two-photon process. The thin films also exhibit a relatively high dielectric constant and a low dissipation factor as well as a good bias voltage stability. Temperature- and frequency-dependent dielectric relaxation has been confirmed. This study suggests that Er3+/Yb3+ co-doped Bi2Ti2O7 thin films can be applied to new multifunctional photoluminescence dielectric thin-film devices.

Structural, photoluminescence, dielectric, and ferroelectric properties of lead-free perovskite Pr3+-doped xK0.5Bi0.5TiO3–(1−x)Na0.5Bi0.5TiO3 (x = 0–1.0) thin films were studied. The thin films were prepared by a chemical solution deposition method combined with a rapid thermal annealing process at 700°C. We observed that the thin film with x = 0.15, corresponding to the morphotropic phase boundary in the solid solution ceramics or single crystal bulk counterparts, showed a very large dielectric constant and a high remanent polarization, as well as a strong red emission at 611 nm assigned to 1D23H4 transitions of the Pr3+ ions. In addition, this study also indicates that the morphotropic phase boundary in xK0.5Bi0.5TiO3–(1−x)Na0.5Bi0.5TiO3 thin films might be probed by photoluminescence probe of Pr3+ ions because the photoluminescence of Pr3+ ions is very sensitive to the phase structure changes.

Strong upconversion photoluminescence and large ferroelectric polarization were observed for the first time in layered structure Er3+–Yb3+–W6+ triply substituted bismuth titanate thin films. The thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by chemical solution deposition. Two green emission bands and a red one were observed in the upconversion photoluminescence spectra for all the films pumped by a 980 nm laser diode, which correspond to 2H11/2, 4S3/2, and 4F9/2 to 4I15/2 transitions of Er3+ ions, respectively. A two-photon energy-transfer process was confirmed by the power dependence of emission intensity. Compared with that of Er3+–Yb3+-substituted bismuth titanate thin films, the improved photoluminescence is related to the reduced defects such as oxygen vacancies due to B-site (Ti4+) substitution by W6+ ions, while the large ferroelectric remnant polarization can be attributed to the increased structure distortion and the reduced oxygen vacancies due to cosubstitution of A-site (Bi3+) and B-site (Ti4+) by Er3+, Yb3+, and W6+ ions, respectively. The combination of the strong upconversion photoluminescence and the good ferroelectric properties in the thin films would open the possibility of realizing novel multifunctional optoelectronic integration device applications.

We report on growth of 25%Bi(Ni0.5Ti0.5)O3–75%PbTiO3 (25BNiT–PT) solid solution thin films and good electrical properties such as high remanent polarization, high dielectric constant, and low dissipation factor. The thin films prepared on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition were well crystallized with a phase-pure perovskite structure. Well-saturated P–E hysteresis loops were observed with a much larger remanent polarization than that of corresponding ceramic counterparts reported before in literature. The remanent polarization Pr and coercive field Ec were 40.9 μC/cm2 and 117 kV/cm, respectively, for the thin films annealed at 650°C. The thin films had a high dielectric constant of about 400–500 and a low dissipation factor of 0.03 at a frequency of 1 kHz. The good polarization characteristics of the thin films are very significant for high-temperature ferroelectric device applications.

Pr3+/La3+-codoped Bi4Ti3O12 (BPLT) ferroelectric thin films were prepared on fused silica and Pt/TiO2/SiO2/Si substrates by the chemical solution deposition method, and their photoluminescence and electrical properties were investigated. Different from Pr-doped ATiO3 (A=Sr, Ca) titanate thin films showing a red emission with the highest emission peak at 612 nm, BPLT thin films exhibited a strong blue–green emission at 493 nm. This can be ascribed to their difference of host lattice between Pr-doped titanate with a simple perovskite structure and BPLT with a bismuth-layered perovskite structure and/or the difference of site symmetry of Pr ions. It was also found that the luminescent intensity was enhanced by the incorporation of La3+ ions into Pr3+-doped Bi4Ti3O12 (BPT) thin films. Meanwhile, the introduction of La3+ also greatly enhanced the ferroelectric properties of the BPT thin films. The dual enhancement of photoluminescence and ferroelectric polarization can be attributed to crystallization improvement of the BPLT thin films. It is expected that BPLT thin films can find potential applications in new multifunctional photoluminescence ferroelectric thin-film devices.

KxBa1−xGa2−xGe2+xO8 (0.6≤x≤1) polycrystalline ceramics are potential materials for glass-free low-temperature cofired ceramics (LTCC) substrates. We have made a comprehensive study of the kinetics of the monoclinic-to-monoclinic P21/a⇔C2/m phase transition. The low-temperature-stable P21/a phase with a high Q×f value was synthesized using a subsolidus method and was well sintered at the LTCC temperature with a H3BO3 additive. A good combination of low sintering temperature (910°–920°C), high Q×f values (96 700–104 500 GHz), low permittivities (5.6–6.0), and a small temperature coefficient of resonant frequency (∼−20 ppm/°C) was obtained for ceramics with x=0.67 and 0.9 and with 0.1 wt% of H3BO3.

Thermal expansion behaviors of Ba6−3xLn8+2xTi18O54 (Ln=La, Nd, and Sm, x=0.5, 0.67, and 0.75) ceramics were determined by dilatometric measurement. The samples of all investigated compositions expanded nearly linearly with increasing temperature in the range of 20°–1200°C. Their thermal expansion coefficients were determined to be 10.7–11.4 ppm/°C. A discontinuous change in sample size was observed at about 1350°C for each composition, indicating the existence of a phase transition. As determined by the high-resolution X-ray diffraction analysis, the phase constitution and the lattice parameters of Ba6−3xSm8+2xTi18O54 ceramics were maintained in the quenched samples. The origin of the phase transition was discussed thoroughly. Phase equilibrium in the BaTiO3–Ln2/3TiO3 system was reviewed by considering the phase transition.

Tin (Sn) substitution for titanium (Ti) was investigated in Ba6−3xNd8+2xTi18O54 (x=1/2, 2/3, and 3/4) ceramics. A small amount (z

xBiAlO 3 -(1-x)PbTiO 3 (xBA-PT, x = 0-0.1) solid solution thin films were prepared on indium tin oxide-coated glass substrates using a chemical solution deposition method at an annealing temperature of 600"C, and the effects of bismuth aluminate (BA) content on the structural, dielectric, and ferroelectric properties of the thin films were investigated. Formation of the solid solution thin films has been confirmed by XRD and Raman analysis. The thin films crystallize in the perovskite structure without the formation of any detectable secondary phase. With increasing BA content, the thin films transform the tetragonal phase into a pseudocubic phase. When x is 0.08, the thin film exhibits high dielectric constant and large remanent polarization (2P r ) values, which are 384 and 58 μC/cm 2 , respectively. In addition, the dielectric loss and the leakage current density were considerably reduced by adding BA to the thin films.

The effect of La substitution for Sm was investigated in Ba6−3x(Sm1−yLay)6+2xTi18O54 (x=0.5) ceramics in the entire range of y (0∼1.0). X-ray diffraction (XRD) analysis indicated that the phase constitution of the present ceramics was sensitive to y, and an abnormal phase transition from the tungsten bronze-type to a new Ba16Ce32Ti64O192-type solid solution was determined at y=0.6–0.9. The crystal structure of the new phase was refined by Rietveld refinement. The stability of the Ba16Ce32Ti64O192-type structure was discussed with the ordering of cations and the average radius of Ln3+. The Ba16Ce32Ti64O192-type phase was observed only in the sintered pellets but not in the loose powders in the investigated temperature range of 1200°–1350°C. A differential scanning calorimetric analysis (DSC) was performed for investigating the thermal effect of the phase transition. Discontinuous dielectric properties were observed corresponding to the phase transition. The Ba16Ce32Ti64O192-type phase has a much higher dielectric constant, a lower quality factor, and a larger positive temperature coefficient of resonant frequency at microwave frequencies in comparison with the tungsten bronze-type phase. Besides, the dielectric loss of the Ba16Ce32Ti64O192-type phase is much lower (tan δ∼10−4) at frequencies below 108 Hz, while the dielectric constant is insensitive to the frequency.