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Novel Mn4+-activated KLaMgWO6 red phosphors with different Mn4+ concentrations were successfully synthesized via a high-temperature solid-state reaction method. The phase formation, microstructure, photoluminescence properties, decay lifetimes and internal quantum efficiency were discussed to analyze the properties of the as-prepared phosphors. The samples belonged to monoclinic crystal system with enough WO6 octahedrons that provided suitable sites for Mn4+ ions. Upon the excitation of 348 nm, KLaMgWO6:Mn4+ phosphors gave bright far-red emission around 696 nm due to the 2Eg→4A2g transition of Mn4+ ions. The critical concentration of Mn4+ was 0.6 mol% and the concentration quenching mechanism belonged to electric multipolar interaction. Besides, the CIE chromaticity coordinates of the KLaMgWO6:0.6%Mn4+ phosphor were (0.7205, 0.2794) which located in deep red range, and its color purity reached up to 96.6%. The KLaMgWO6:0.6%Mn4+ sample also exhibited high internal quantum efficiency of 43%. All of the admirable optical properties indicate that the KLaMgWO6:Mn4+ phosphors can be applied to indoor plant growth illumination.

The precipitation of monoclinic Na3ScF6 nanocrystals from aluminosilicate glass with specially designed compositions of SiO2-Al2O3-Na2O-NaF-ScF3-YbF3 was achieved for the first time. Impressively, competitive nanocrystallization of cubic NaYbF4 and monoclinic Na3ScF6 has been evidenced to be dependent on Na+ content and F/Na ratio in glass. Adopting Er3+ and Eu3+ dopants as structural probes, optical spectroscopic analyses verified that these emissive centers preferred to partition into NaYbF4 nanocrystals rather than Na3ScF6 ones.

In this study, bundle-shaped β-NaYF4 microrods with uniform morphology and good monodispersity were successfully synthesized via a facile, template-free and environmentally-friendly hydrothermal route. According to the time-dependent experimental results, the formation mechanism for the crystal phase and shape evolution process has been proposed via the Ostwald-ripening process. Under single wavelength irradiation at 250 nm, intense multi-color downconversion emissions can be obtained by co-doping Ce3+, Gd3+ and X3+ (X = Eu, Tb and Dy) into the as-synthesized β-NaYF4 crystals, in which Gd3+ plays an intermediate role in transferring the excitation energy from sensitizer Ce3+ to activators X3+. Furthermore, the temperature-dependent emission behaviors of β-NaY0.8Gd0.2F4:Ce3+/X3+ dual-emitting products have been systemically investigated to explore their possible application in self-calibrated optical thermometry. Impressively, the high temperature sensitivity, good signal discriminability and excellent thermal stability of the investigated dual-emitting phosphors making them a promising candidate for temperature sensing.

The quadratic electrostrictive effect possesses several unique advantages over the piezoelectric effect, including a fast response speed, temperature stability, hysteresis-free characteristic. In this regards, we report a 0–3 type 0.92(Bi .5 Na .5 )TiO 3 −0.06BaTiO 3 −0.02(K .5 Na .5 )NbO 3 :6 wt% Bi 4 Ti 3 O 12 (BNT-BT-KNN: BiT) composite ceramics to achieve the competent electrostrictive effect at room temperature. The electrostrictive behavior of composite ceramics was systematacially explored with respect to driving field, temperature, frequency and cycles. The manufactured composite ceramic is featured by not only large room-temperature electrostrictive coefficient Q 33 of 0.0327 m 4 C −2 but also superior thermal stability in the temperature range from 25 °C to 120 °C. Simultaneously, the gained electrostrictive response exhibited relatively good frequency-dependent and fatigue character. It is demonstrated that construct of a 0–3 type connectivity composite provides a highly effective path to tailor electrostrictive characteristic of BNT-based ceramics. The current study shows a significant advancement in the area of lead-free electrostrictive materials and can inspire potential interest in search for novel BNT-based ceramics with promising electrostrictive effect.

Pairing of large strain response and high d 33 with high T c in (K 0.5 Na 0.5 )NbO 3 -based materials is of high significance in practical applications for piezoelectric actuators. Here, we report remarkable enhancement in the electromechanical properties for (1-x)(K 0.52 Na 0.48 ) (Nb 0.95 Sb 0.05 )O 3 -xCaZrO 3 (KNNS-xCZ) lead-free ceramics through the construction of a rhombohedral ( R )-tetragonal ( T ) phase boundary. We investigated the correlation between the composition-driven phase boundary and resulting ferroelectric, piezoelectric, and strain properties in KNNS-xCZ ceramics. The KNNS-xCZ ceramics with x=0.02 exhibited a large strain response of 0.23% while keeping a relatively large d 33 of 237pC/N, which was mainly ascribed to the coexistence of R and T phases confirmed by the XRD and dielectric results. It was found that pairing of large strain response and high d 33 in KNN-based materials was achieved. As a consequence, we believe that this study opens the possibility to achieve high-performance lead-free electromechanical compounds for piezoelectric actuators applications.

In this study, we propose an effective approach to gain prominent electrostrictive behavior by taking advantage of texture construction in lead-free (Bi 0.5 Na 0.5 )TiO 3 (BNT)-based piezoceramics for actuator applications. The electrostrictive effect was explored systematically in textured 0.90(0.83Bi 0.5 Na 0.5 TiO 3- 0.17Bi 0.5 K 0.5 TiO 3 )-0.10NaNbO 3 (BNT-BKT-NN) ceramics with respect to grain orientation, temperature and electric fields. It was found that the electrostrctive coefficient Q 33 and recoverable strain increase monotonously with the grain orientation increasing. At the optimized microstructure ( F 00 l =92%), a giant Q 33 with nearly purely electrostrictive characteristics was detected to be around ~0.0354 m 4 C −2 , which was far larger than the reported values of Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) and the existing BNT-based electrostrictive materials. Meanwhile, the acquired Q 33 was found to exhibit excellent stability for the highly textured sample under different temperature or electric field conditions. Our achievement demonstrates that the giant electrostrictive properties with superior temperature and electric field stability for textured BNT-BKT-NN ceramic are of great significance in replacing traditional PMN ceramics for actuator applications.

A ternary solid solution Ba(Zr 0.05 Ti 0.95 )O 3 -modified (Bi 0.5 Na 0.5 )TiO 3 –(Bi 0.5 K 0.5 )TiO 3 (BNT–BKT–BZT) was designed and prepared by solid state synthesis. The phase stability and macroscopic electromechanical properties were systematically investigated with an emphasis on the relationship between the structure evolution and strain behavior, and a schematic phase diagram is proposed. Increasing the content of BZT decreased the ferroelectric-to-relaxor phase transition temperature T F-R and induced the reversible transition from the relaxor pseudocubic to ferroelectric rhombohedral phase, giving rise to a promising strain behavior at a critical composition x =0.02 featured by not only high electric-induced normalized strain of S max / E max =503 pm/V but also a relatively small hysteresis compared with existing BNT-based lead-free ceramics. In particular, by limiting the electric driving field to exclude the contribution from the converse piezoelectric effect, a temperature-insensitive S max / E max was obtained in the investigated temperature range from room temperature to 120 °C. Furthermore, a high electrostrictive coefficient ( Q 11 ) of 0.0237 m 4 C −2 was achieved at room temperature for the composition with 10 mol% BZT, that was highly stable within the investigated temperature and electric field ranges.

textured (Ba 0.85 Ca 0.15 )(Zr 0.1 Ti 0.9 )O 3 (BCZT) lead-free piezoelectric ceramics were fabricated by templated grain growth using plate-like BaTiO 3 as template. The effects of orientation degree on the microstructure and resulting changes in dielectric, ferroelectric, piezoelectric, and strain properties were systematically investigated to develop the lead-free piezoelectric materials with an excellent actuating performance. The electromechanical properties were found to increase monotonously with the increase in the degree of texturing and dramatically enhanced for the textured BCZT ceramics in the optimized microstructure compared with randomly-oriented counterparts. Highly textured ceramics showed excellent electromechanical properties of d 33 =462 pC/N, k p =47%, S =0.187%, and S max / E max =621 pm/V at room temperature. These results indicates that the textured ceramics are promising candidates for environmentally friendly actuator devices with high performance.

A series of red-emitting Li 6 Sr(La 1− x Eu x ) 2 Sb 2 O 12 (0 x ≤1.0) phosphors have been prepared via the conventional high-temperature solid-state reaction method. X-ray diffraction, photoluminescence spectra, luminescence lifetimes and temperature-dependent decays were used to characterize the fabricated samples. The excitation and emission spectra indicated that the phosphor can be excited effectively by ultraviolet (393 nm) and blue (463 nm) light and emitted intense red light peaked at around 611 nm corresponding to the 5 D 0 – 7 F 2 transitions of Eu 3+ . In addition, the impact of the Eu 3+ content on the emission intensity was investigated. The results showed that the concentration quenching was not observed due to the large distance ions which substitute the La 3+ ones in the hosts. The prepared Li 6 SrLaEuSb 2 O 12 phosphor exhibited high thermal stability with only 8% loss from 293 K to 553 K, and its quantum efficiency reached as high as 42.46% under the excitation of 393 nm. A white light-emitting diode with high luminous efficacy of 124.20 lm/W and preferable CIE coordinate of (0.3186, 0.3333) was fabricated by combination of Li 6 SrLa 2 Sb 2 O 12 :Eu 3+ red phosphor and commercial Y 3 Al 5 O 12 :Ce 3 + yellow phosphor on a blue-InGaN chip.

Hexagonal NaYF 4 microcrystals with controllable morphologies and tunable sizes have been successfully synthesized by a facile hydrothermal method. The influences of the molar ratios of trisodium citrate (Cit 3− ) to Y 3+ and pH values on the phase and morphology evolution were investigated and discussed in detail. It is found that trisodium citrate and pH value as two significant external factors play key roles in the formation of the anisotropic architectures of β-NaYF 4 microcrystals. Taking hexagonal β-NaYF 4 microprisms as a candidate, the possible formation mechanism has been proposed on the basis of time-dependent experiments. In addition, the upconversion (UC) luminescence properties of β-NaYF 4 :Yb 3+ /Er 3+ samples were systematically studied and discussed. The results reveal that the UC luminescence properties are strongly dependent on their morphologies and sizes. This study not only provides important information for shape-controlled synthesis of other complex rare earth fluoride compounds, but also gives a reference for exploration of morphology- and size-dependent UC luminescence properties.

A novel Ca 2.89 Mg 0.11 (PO 4 ) 2 :Eu 2+ single-phase white light-emitting phosphor was synthesized by solid-state reactions and its crystal structure and luminescence properties were investigated. The Ca 2.89 Mg 0.11 (PO 4 ) 2 :Eu 2+ phosphor was found to have a trigonal structure with a space group R3c. The broad excitation spectra, ranging from 250 to 400 nm, matched well with near-UV LED chips. The much wider emission bands from 365 to 675 nm included more than one peak. Furthermore, the intensity of the peak at about 413 nm gradually decreases, while those in longer wavelengths gradually increase with the increase in Eu 2+ concentration. Correspondingly, the emission hue varied from purplish-white to white and eventually to yellowish-white under 365 nm excitation. These results suggested that the Ca 2.89 Mg 0.11 (PO 4 ) 2 :Eu 2+ phosphor was a color tone tuning single-phase white light-emitting phosphor. Therefore, Ca 2.89 Mg 0.11 (PO 4 ) 2 :Eu 2+ is expected to be a promising candidate for white LEDs.

A transparent Ce 3+ : Y 3 Al 5 O 12 (Ce: YAG) glass ceramic with high quantum yield of 94% and improved thermal-quenching feature, using low-cost Sb 2 O 3 -based glass as host, is developed to replace the conventional phosphor/organic-resin color converter. The constructed glass–ceramic-based white-light-emitting diode exhibits a high luminous efficiency of 130 lm/W, superior to that of the conventional pc-WLED (95 lm/W), and a correlated color temperature of 5298 K as well as a color rendering index of 65, which reveal the prominent feasibility of the present glass ceramic material in high-power organic-resin-free WLED application.

Eu 3+ doped glass ceramics embedding ZnO quantum dots (QDs) were successfully prepared by a sol–gel method. High-resolution transmission electron microscopy (HRTEM) observations revealed that ZnO QDs with size of 3–6 nm precipitated homogeneously among the SiO 2 glassy matrix after thermal treatment of the precursor sample. Such glass ceramics show a high transparency in the visible-infrared range due to the much smaller size of the ZnO QDs than the wavelength of the visible light. The emission and excitation spectra of the samples with various ZnO contents were studied. Based on Judd–Ofelt theory, the intensity parameter Ω 2 was evaluated to investigate the change of the environment around Eu 3+ in samples with and without QDs.

Transparent glass ceramics containing YF 3 nano-crystals were fabricated by heat treatment of the SiO 2 –Al 2 O 3 –NaF–YF 3 –LnF 3 (Ln = Er, Yb) glasses. X-ray diffraction and transmission electron microscopy analyses evidenced the homogeneous distribution of spherical YF 3 nano-crystals sized 25–30 nm among the glassy matrix. Energy dispersive X-ray spectroscopy measurement, combined with the Stark splitting of the absorption and emission bands, verified the incorporation of Er 3+ and Yb 3+ ions into YF 3 nano-crystals. The infrared to visible up-conversion emission of Er 3+ intensified with the increasing of Yb 3+ concentration, ascribing to the increase of the efficiency of non-radiative energy transfer from Yb 3+ to Er 3+ which exceeded 45% for the 0.5Er 3+ /1.0Yb 3+ co-doped sample. The up-conversion luminescence at 545 and 660 nm were affirmed coming from two-photon excitation process.

Er3+:SrF2–SiO2–Al2O3 transparent glass ceramic was prepared by a sol–gel method. The effect of Al3+ doping on the microstructures and luminescence properties of the materials was investigated by the X-ray diffraction (XRD), the transmission electron microscopy (TEM) and the absorption and luminescence spectra measurements. It was evident that Al3+ ions play an important role in improving the structure stability of the glass ceramic by suspending the crystallization of the oxide glassy matrix. The upconversion luminescence of the Al3+-doped glass ceramic was greatly enhanced and visible by the naked eyes, which implies the potential application of this material in the field of solid-state displays.