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The phase transition temperature (e.g., that of orthorhombic‐tetragonal TO‐T) of relaxor ferroelectrics are commonly obtained through electrical method (i.e., temperature dependence of dielectric constant), and the samples need to be coated with metal electrode and tested by a sophisticated impedance analyzer. This contact measuring method is inefficient, inconvenient and easy to damage the sample surface, inapplicable to transparent ferroelectrics. Here, we successfully fabricated Bi/Sm co‐doped K0.5Na0.5NbO3 transparent ceramics with photoluminescent behavior and relaxor‐like ferroelectricity, which simultaneously realized TO‐T monitoring and temperature sensing via fluorescence intensity ratio (FIR) technology. This simple, rapid, noncontact and nondestructive optical way displays small TO‐T deviation (merely 0.78%) compared to the electrical method. And the temperature‐dependent optical characteristics and coercive electric field all present abrupt changes, whose abnormal temperature regions are in accordance with that around TO‐T. In addition, the maximum absolute sensitivity and relative sensitivity of the ceramics reach 0.0072 K−1 (at 533 K) and 0.0111 K−1 (at 453 K), respectively, exhibiting superior optical temperature sensing performance. The tactical use of FIR technology is of great significance for widening the applications of luminescent‐ferroelectric transparent ceramics. [ABSTRACT FROM AUTHOR]

Traditional solid‐state luminescent materials (e.g., phosphors and microcrystalline glasses) have attracted extensive attention due to their high energy efficiency and long lifespan. However, their application scope is limited by complex compositions and manufacturing processes, as well as single‐function. In this study, solid‐state reaction was utilized to prepare transparent‐ferroelectric (K0.5Na0.5)NbO3 (KNN) ceramics by simply codoping with Dy3+ and Sr2+, providing possibilities for large‐scale production. Ceramics exhibit high optical transmittance, high‐quality white‐light emission and relaxor ferroelectric feature. Under irradiation of UV light, photochromic behavior occurring in the ceramics, resulting in modulating the optical performances, especially quality of emitted white light. Multifunctionality can expand latent applications of KNN‐based ceramics from white light‐emitting diodes to modulated optoelectronic devices. [ABSTRACT FROM AUTHOR]

Most photochromic ceramics can back up post-irradiation to achieve color state transition. Unfortunately, color recovery usually requires exposure of material to external physical fields (such as light and heat), which severely limits the application as a convenient energy building material such as smart windows. Here, we report a kind of sodium niobate translucent ceramics whose photochromic effect can be completely self-recoverable without any external physical field stimulation. Based on the analysis of time-response transmittance, up-conversion emission spectra and thermoluminescence spectra, the behavior of carrier migration and trap capture/release in the process of self-recovery photochromic reaction has been proposed. It is believed that the emergence of intermediate trap level is an important factor to produce this spontaneous behavior. Moreover, by controlling the amount of rare earth doping and designing two types of materials with different carrier behaviors, Sm/Er-codoped NaNbO 3 ceramics are regarded as an appropriate candidate for tracing the time of light irradiation and intelligent regulation of smart building materials. This work can promote the fundamental understanding and practical applications of self-recoverable photochromic bulk materials. [ABSTRACT FROM AUTHOR]

Smart windows with adjustable transmittance via physical stimuli are eagerly desired for sorts of energy‐saving lighting systems. However, reciprocal trade‐off relationship such as high transparency and coloration/discoloration ability exists in smart windows, not conducive to optical‐electrical coupling and leap in performance. Substituting for common composites utilized in smart windows, here, single transparent ceramic‐based smart windows are reported through composition design and defect management strategies to regulate the optoelectronic performances and break off the contradictions between optical transmittance, photo‐thermochromism and electrical conductivity. By first principles calculations and precisely tuning Er3+, Ba2+, Sr2+ concentrations in non‐stoichiometric Er‐doped (K0.5Na0.5)NbO3‐(Ba, Sr)TiO3, the fabricated ceramics exhibit brilliant transparency and multi‐mode dramatical and reversible modulations of pellucidity, photoluminescence intensity, along with conductivity (over fivefold variation), enabling prominent optoelectronic information storage and modulating capacity in vivid potential applications, such as easy‐readout/erasable optical memorizers, photo‐memristors and anti‐counterfeiting displays. [ABSTRACT FROM AUTHOR]

The Eu-doped K0.5Na0.5NbO3 pellucid ceramics were first prepared via a conventional solid-state reaction, and they exhibited light illumination-induced high-contrast photochromism of both optical transmittance and photoluminescence behaviors. Through thermal treatment, the optical performances could return to their initial states and displayed excellent reversibility. Eu3+ ions were selected as the luminescent activator for detecting the local environment of the K0.5Na0.5NbO3 host. Meanwhile, the effects of the amount of Eu3+ present on phase structures, microstructures, optical transmittance and photoluminescence intensities were systematically investigated. The results suggest that Eu-doped K0.5Na0.5NbO3 transparent ceramics possess multifunctionality including photochromism, photoluminescence and optical switching properties, and that they exhibit promising potential for non-destructive optical data storage application. [ABSTRACT FROM AUTHOR]

The (K0.5Na0.5)0.95Li0.05Nb0.95Bi0.05O3‐1mol% Er2O3 transparent ceramics were prepared by a pressureless sintering method. The fabricated transparent ceramics not only exhibit high optical transmittance (85.3%) due to dense microstructure (nanoscale size grains), but also show the photochromism‐induced light scattering and reversible upconversion (UC)‐switching properties by visible light irradiation. Upon 407 nm light irradiation, the optical transmittance intensity is significantly decreased, showing a strong light scattering (ΔAbs = 28.3%). The light scatting degree can be quantitatively reflected by Er3+ ion UC emission, and could be recovered to its initial optical transmittance based on photochromic reactions. Meanwhile, the transparent ceramic is found to maintain good energy storage properties with higher W (5.87 J/cm3) and Wrec (1.96 J/cm3) under a higher electric field of 260 kV/cm. These results suggest that Er3+ doped (K0.5Na0.5)NbO3 transparent ceramics are promising for the modulation of light scattering and the design of photoelectric multifunction devices. [ABSTRACT FROM AUTHOR]

Photochromic (PC) luminescent ferroelectric materials have aroused great interest because of their potential applications in optical information memories, optical switches and bio-imaging. However, those materials are basically opaque. In this work, we prepared a PC luminescent K 0. 5 Na 0. 5 NbO3-based ferroelectric transparent ceramic by modifying with Eu 3 + , Ba 2 + , Ti 4 + and Sr 2 + , which not only have good optical transmittances (∼ 60% at 900 nm), moderate ferroelectric properties and down-conversion photoluminescence (PL) properties, but also exhibit reversible PC behavior. After the illumination by xenon lamp, the colors of the ceramics change from pale green to gray, and then reversibly recover to their initial state via thermal stimulus (200∘C for 10 min). Interestingly, both the optical transmittances and PL intensities can be effectively tailored by controlling the PC reaction process. The results suggest that the ferroelectric transparent ceramics are promising for the modulation of photoenergy and the design of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Transparent Er3+/La3+ co-doped (K 0.5 Na 0.5)NbO 3 ceramic was prepared by pressureless sintering. The XRD result shows that it possesses high symmetrical pseudo-cubic perovskite structure without impurity phase. The ceramic owns fine grains with the average size of ∼350 nm, uniform grain distribution, low porosity and high density. The optical transmittance of 0.3-mm ceramic is up to ∼60% in the visible region. Additionally, the ceramic has good dielectric properties with the relaxor-like behavior. Under an excitation of 980-nm, the temperature-dependent up-conversion luminescent color of Er3+ is stable below 523 K and adjustable (changing from green to tangerine color as temperature increases) above 523 K. The ratio of red to green emission intensity with temperature can provide a non-contact luminescent route to roughly detect the phase transition of this ferroelectric ceramic. Furthermore, the fluorescence temperature sensing performance of the ceramic was investigated and the maximum sensitivity is 0.003/K at 380 K. Due to optical, PL and electrical properties, the transparent ceramic shows potential in the application of electro-optical coupling devices. [ABSTRACT FROM AUTHOR]

High optical temperature sensing properties based on rare‐earth‐doped (K,Na)NbO3‐based ferro‐/piezoelectrics have attracted much attention due to their potential application in novel optoelectronic devices. Here, we fabricated Ho3+‐doped (K0.5Na0.5)NbO3–SrTiO3 transparent ceramics by conventional pressureless sintering. Their microstructures, transmittances, up‐conversion photoluminescence, and optical temperature sensing properties have been characterized in details. Because of the cubic‐like phase, dense, and fine‐grained structure as well as relaxor‐like feature, the ceramics exhibit high transmittance (~70%) in the near‐infrared region. Owing to Ho3+, green and red up‐conversion emissions have been observed, which can be easily modulated by temperature. The ceramics have stable emission colors (<200°C) and superior temperature‐modulating emission color‐tunable performance (>200°C). Furthermore, the temperature sensing behavior based on the thermally coupled levels (5F4, 5S2) of Ho3+ has been analyzed by a fluorescence intensity ratio technique. The transparent ceramics possess outstanding optical temperature sensitivity (~0.0096/K at 550 K), higher than most rare‐earth‐doped materials (e.g., ceramics, glasses, and phosphors). [ABSTRACT FROM AUTHOR]

Abstract Er-doped K 0.5 Na 0.5 NbO 3 -SrTiO 3 transparent ceramics were fabricated by traditional pressureless sintering. The dual effects of Er3+ and SrTiO 3 contents on the microstructures, optical transparencies and optoelectronic properties of the ceramics were investigated. The introduction of Er3+ and Sr2+ results in decreasing grain size and generating cation vacancies, affecting the density and uniformity of the ceramics. The ceramics exhibit superior transmittance: T ∼55% in the visible region (760 nm) and ∼75% in the infrared region (2000 nm), which is dependent on optical band gap energy. In terms of electrical properties, the ceramics also possess relaxor-like characteristics, low dielectric loss and suitable piezoelectric constants. Due to Er3+, the ceramics exhibit composition-tunable green and red up-conversion photoluminescence emissions, whose intensities are related to the crystal symmetry. Combined with good optical and electrical properties, the ceramics open up potential applications in the electrical/optical interdisciplinary field, such as visible displays, solid-state lasers and transparent electronic devices. Highlights • Transparent ceramics Er-doped KNN-SrTiO 3 were prepared by pressureless sintering. • Optical transparencies of ceramics can be regulated by the content of Er and SrTiO 3. • The relaxor-like characteristics and good dielectric properties have been obtained. • The ceramics exhibit composition-tunable up-conversion photoluminescence. • The transparent ceramics can be applied in electrical/optical interdisciplinary field. [ABSTRACT FROM AUTHOR]

Ho3+‐doped (K0.5Na0.5)NbO3‐based transparent ceramics have been prepared via pressureless solid‐state method. The ceramics possess moderate optical transparency with the energy band gap of ~2.9 eV and submicron‐sized grains (<500 nm). The temperature‐dependent dielectric properties and ferroelectric polarization‐electric field hysteresis loops demonstrate that the ceramics own relaxor‐like characteristics. The up‐conversion photoluminescence and optical temperature sensing properties of the ceramics have been investigated. The temperature dependence of photoluminescence provides a fluorescent method to detect phase transitions, which can be expanded to other ferroelectric systems. The outstanding optical temperature sensitivity (~0.0075/K at 430 K) of the ceramic is higher than many other rare‐earth‐doped ceramics or glasses. These results suggest that the Ho3+‐doped (K0.5Na0.5)NbO3‐based transparent ceramics are promising lead‐free transparent materials for multifunctional applications, especially in temperature sensing devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel defect engineering is proposed to significantly refine the grain size of energy storage ceramics. • Achieving simultaneously high energy storage density, a rapid discharge time and superior transparency. • In-depth explanations are supported by the DFT calculations and the finite element analysis. • Bright-field TEM revealed the presence of ultrafine grains, PNRs and highly symmetric phase. Ceramic-based transparent dielectric materials are regarded as the best candidates for advanced energy storage and conversion materials because of their outstanding optical and electric properties. Nevertheless, due to the presence of low density, low band gap energy and large grain size, it is difficult to simultaneously obtain high energy storage density and high optical transmittance in lead-free based ceramics, which limiting their further development of practical applications. In this work, the relaxor ferroelectric ceramics of x mol% Er3+-doped 0.91 K 0.5 Na 0.5 NbO 3 -0.09Ba m Sr n TiO 3 (xEr-Sr m Ba n) were constructed via A-site non-stoichiometric defect engineering. It is worth noting that excessive addition of Sr and Ba, especially Sr, can significantly refine the grain size and domain size on account of vacancy-related defect pinning. Finally, high energy storage density (W = 6.39 J/cm3, W rec = 3.42 J/cm3) together with high optical transmittance (∼72% at 900 nm) can be achieved simultaneously in 0.25Er-Sr 1 Ba 0.5 due to the exist of dense structure, ultrafine grain size (<100 nm), small-sized nano-microdomains (i.e., PNRs, < 50 nm) and large bandgap energy (∼3.10 eV). Furthermore, a fast discharge time of 42 ns can also be realized. The above results indicate that the present study helps to promote the development of advanced transparent energy storage and conversion materials. [ABSTRACT FROM AUTHOR]

Transparent ferroelectrics with high piezoelectricity are highly desirable for acousto-optic-electrical multifunctional coupling devices. However, it is challenging to simultaneously achieve high piezoelectricity and perfect transparency in lead-free piezoelectric ceramics because of the contradiction between the inherent characteristics of traditional high piezoelectricity and the transparency. Here, we demonstrate an efficient method to tailoring the microstructure in originally poor piezoelectricity fine-grain KNN-BNN ceramics to simultaneously exhibit excellent transparency, an superior piezoelectric coefficient (∼185 pC/N, highest in KNN-based transparent ceramics), an excellent EO coefficient (∼84 pm/V), and high T c (∼350 °C). Combining the multiple in-situ characterizations and DFT simulations, we found that both the piezoelectricity and EO effect of fine-grain KNN transparent ceramics can be greatly improved without greatly reducing the transparency via tailoring the structure of phase and domains to enhance local inhomogeneity, enabling prominent acousto-optic-electrical multifunctional coupling in vivid potential applications, such as self-energy-harvesting touch screens, invisible robotic devices and electro-optic (EO) devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Dielectric ceramics have attracted wide interest in the field of energy storage. However, high energy density depends on large electric field, seriously threatening the safety of workers and distribution equipment. This work reports excellent energy storage performance of Bi 0.5 Na 0.5 TiO 3 -based transparent ceramics at low electric field. A schematic diagram shows the designed TPC and the corresponding ceramics using the collaborative optimization strategy, including a series of measures (enhancing the energy-storage performance, broadening the stable dielectric platform and reducing both grain and domain sizes). And a practical application scenario for rescue signal transmission when disasters occur is conceived. [Display omitted] • Bi 0.5 Na 0.5 TiO 3 -based transparent energy-storage ceramics were prepared. • High W rec of 3.46 J cm−3 was obtained at a low electric field of 197 kVcm−1. • High stability (Δη/η < 2.2 % and ΔW rec / W rec < 3.1 %) was obtained between 25–200 °C. • Ho/Yb codoping in the ceramics realize real-time fluorescence temperature sensing. • Ceramic-based TPCs can be used in light-pulse signal generator for search and rescue. Transparent dielectric ceramics with ultrafast discharge rates and gigantic power densities are ideal candidates for transparent pulse capacitors (TPCs). However, the requirement of a high external electric field and inferior temperature stability hinder practical applications. (Bi 0.5 Na 0.5)TiO 3 -based ceramics exhibit large polarization and two characteristic dielectric peaks, easy to obtain high energy-storage density under low electric fields (low- E) and maintain stable energy-storage performance (ESP) within a wide temperature range. However, their low optical transmittance (T %) limits their development into TPCs. In this work, to concurrently obtain high T % and excellent ESP and stability under low- E conditions, we propose a collaborative optimization strategy for determining the regulations of grain size, bandgap energy and domain structure. The results show that the pellucidity and energy-storage characteristics improve with decreasing grain and domain sizes. A relatively high T % of 45.6 % (at 710 nm) and recoverable energy-storage density (W rec ∼ 3.46 J cm−3 at 197 kV cm−1) are obtained for the (1- x)[0.85(Bi 0.5-3 y Na 0.5- y Yb 3 y Ho y TiO 3)-0.15SrZrO 3 ]- x BaHfO 3 ceramics. Additionally, the dielectric temperature stability also results in splendid storage temperature stability (Δ W rec / W rec < 3.1 % in the range of 0–200 °C). Importantly, codoping Ho/Yb in the ceramics induces excellent fluorescence temperature sensing feature. The multifunctional TPCs have application potential in the field of search and rescue signal transmission, providing ideas for developing novel optoelectronic devices. [ABSTRACT FROM AUTHOR]

The lead-free Er 3+ -doped (K 0.48 Na 0.48 Li 0.04 )(Nb 0.96 Bi 0.04 )O 3 (KNLNB-Er-x) ceramics were fabricated by conventional pressureless sintering. They possess a tetragonal perovskite phase with dense microstructure. High transmittances of the ceramics are obtained both in the visible and infrared regions. The optical band gap energies of them are 3.07–3.11 eV, close to other KNN-based materials. The relaxor-like characteristics, good dielectric, ferroelectric and piezoelectric properties of the ceramics have been obtained. The up-conversion photoluminescence spectra have been studied and obvious color-tunable emissions have been observed by modulating temperature. The fluorescence intensity ratio (FIR) value based on green emissions at 533 and 555 nm in the temperature ranging from 300 to 750 K have been investigated, giving the maximum sensitivity of ~ 0.0038 K −1 . Furthermore, the FIR technique opens up a method to detect the Curie temperature of the ceramics. Owing to both optical and electrical properties, the KNLNB-Er-x transparent ceramics could be a promising candidate in the application of color-tunable solid-state lightings, optical temperature sensors, and electrical-optical coupling devices. [ABSTRACT FROM AUTHOR]

Inorganic photochromic (PC) materials are increasingly considered as important media for optical information storage and multi-level encryption anti-counterfeiting. However, most traditional materials are based on their static properties, posing a serious security threat to the stored information. To address this issue, a strategy is proposed for kinetics-tunable PC (K 0.5 Na 0.5)NbO 3 ceramic that comprehensively utilize the static and dynamic characteristics of matters. The prepared (K 0.5 Na 0.5) 0.95 Sr 0.04 Pr 0.01 NbO 3 (SP-y) ceramics displayed two different excellent optical properties and distinct applications (smart windows and dynamic information storage) simply by adjusting sintering temperature (y). The sample SP-1180 exhibited high transparency (∼62% at 780 nm) while SP-1150 possessed ultrafast response time (3 s) and extremely high coloration contrast (ΔR I = 91%). More importantly, the kinetics of photoreaction could be modulated by varying illumination wavelength and time. Furthermore, a new anti-counterfeiting or optical storage method was designed by constructing SP-1150 with different PC properties. The encoded or stored information was recorded using two commercial lasers (370 & 405 nm or 370 & 520 nm), suggesting that the security level of this anti-counterfeiting design could be significantly improved. This work will drive more innovative designs in smart windows, high-security dynamic anti-counterfeiting and optical storage applications in the future. In this work, the prepared (K 0.5 Na 0.5) 0.95 Sr 0.04 Pr 0.01 NbO 3 (SP-y) ceramics displayed two different excellent optical properties and distinct applications (smart windows and dynamic information storage) simply by adjusting the sintering temperature. [Display omitted] • Sr/Pr doped KNN ceramics display different optical properties and applications. • The transmittance of ceramic sintered at 1180 °C is up to 62% at 780 nm. • The ceramic sintered at 1150 °C exhibits excellent PC performance. • Coupling relationship between PC and PL intensity is established. • The design of dynamic anti-counterfeiting and optical storage is implemented. [ABSTRACT FROM AUTHOR]