Smart white lighting and multi-mode optical modulations via photochromism in Dy-doped KNN-based transparent ceramics

Dy³⁺-doped K_0.5Na_0.5NbO₃-Ba(Sc_0.5Nb_0.5)O₃ transparent ferroelectric ceramics, a novel smart white-lighting (WL) photochromic (PC) material, were prepared by conventional pressureless sintering. The ceramics exhibit high optical transmittance (~67% at 1800 nm), good photoluminescence (PL) performance, high-quality WL, and moderate electrical properties. Meanwhile, high-contrast modulations of optical transmittance and PL intensity (with the maximal modulating values of 20.5% and 57.4%, respectively) have been realized via PC behavior by alternating the illumination of UV light and thermal stimulus. In particular, the reversible modulations of WL intensity, color coordinates, correlated color temperature, and color purity have been achieved through the PC regulation to the intensity ratio of yellow/blue emission. Definitively, based on the effect of intrinsic defects and extrinsic defects (Ba⁴⁺/Sc^3-x) on the PL properties, the PC mechanism in KNN-based material has been further complemented. The transparent ceramics should be a promising material in white LEDs and optoelectronic multifunctional devices.     

Preparation and photochromic behavior of borosilicate aluminate glass for smart window and curtain wall applications

Sunlight-induced photochromic glass exhibits attractive application prospects in the field of architecture materials. In this work, a series of borosilicate aluminate photochromic glasses containing AgCl nanocrystals were prepared. The photochromic property and mechanisms were systematically investigated. The color of the glass turned from transparent to black (or dark grey) under the irradiation of 365 nm ultraviolet light (or sunlight). Placing in a dark environment, the color of photochromic glass gradually restores to its initial state. From the results of in situ TEM and XPS measurement, it is found that the photochromic and self-bleaching behavior of borosilicate aluminate glass originated from the formation and decomposition of silver nanoparticles. Utilizing the photochromic and self-bleaching properties of the glass, the transmittance of the glass could be reversibly modulated. The cycle measurement shows excellent repeatability, demonstrating the potential application of AgCl-contained borosilicate aluminate photochromic glass in the fields of smart building windows and curtain walls.     

Photochromic contrast optimization based on hafmium-based ceramics for optical information storage: Component adjustment and ion-doping

Herein, we report strategies combining component adjustment and ion doping for the development of photochromic materials with high color-changing contrast. Sr_0.05Ba_0.95HfO₃: Eu³⁺ ceramics showed reversible photochromism from off-white to dark brown under the alternating action of 254 nm UV light and heat treatment at 300 °C. This is caused by the capture and release of electrons by defects in the Sr_0.05Ba_0.95HfO₃: Eu³⁺ host such as oxygen vacancies. Under this strategy, the maximum photochromic contrast ratio of 44.81% is achieved, which is a great improvement compared to pure SrHfO₃ (15.91%) and BaHfO₃ (14.98%). The luminescence quenching behavior based on the photochromic reaction can effectively modulate the emission of Eu³⁺. The reversible photochromic properties of Sr_0.05Ba_0.95HfO₃: Eu³⁺ ceramics can be used for repeated writing and erasing of optical information, and the significant body color change improves its resolution in pattern information storage.     

Reversible luminescence modulation of Ho‐doped K0.5Na0.5NbO3 piezoelectrics with high luminescence contrast

A significant luminescence modulation behavior based on photochromic reactions was observed in Ho³⁺‐doped (Na_0.52K_0.48)_0.92Li_0.08NbO₃ ceramics, fabricated by the conventional solid‐state reaction method. Under visible light irradiation (407 nm) for 20 second, the samples changed pale gray from initial pale green, and returned to their original color by a thermal stimulus of 230°C for 10 minutes, showing typical photochromic phenomenon. Under 453 nm excitation, the samples exhibited strong green emission at 551 nm. Interestingly, their green emission intensity can be effectively tailored by controlling photochromic reaction processes (irradiation wavelength and time), and the luminescent modulation ratio (ΔR_t) reaches up to 77%. And, the ΔR_t value has no any obvious degradation after 10 cycles by alternating visible light irradiation and thermal stimulus, showing excellent reversibility. These results make it potential applications in many fields as a kind of multifunctional material.     

Highly responsive photochromic behavior with large coloration contrast in Ba/Sm co-doped (K0.5Na0.5)NbO3 transparent ceramics

Ferroelectrics that simultaneously possess optical transparency and photochromic (PC) behavior have attracted extensive attention for multi-functionality. However, inability to achieve both rapid and large coloration contrast in photo-stimulated ferroelectrics limits their practical application. In this work, we propose a new strategy for realizing rapid photochromism by constructing the intermediate trap level (T₂) in Ba/Sm co-doped (K_0.5Na_0.5)NbO₃ (KNN) ferroelectric transparent ceramics. Specifically, rapid photo-response time of about 2 s was achieved, and the modulation ratios of transmittance and luminescence intensity were 37.6% and 72.6% within 2 s for the ceramics. This highly responsive PC behavior with large coloration contrast is expected to broaden the application of PC materials in optical devices, e.g. photo-sensitive glasses and rewritable information displays.     

Large and reversible in-situ up-conversion photoluminescence modulation based on photochromism via electric-field and thermal stimulus in ferroelectrics

A large and reversible up-conversion (UC) photoluminescence modulation via both thermal and electric-field stimulus based on the photochromic reactions has been developed in a novel material: Er³⁺/Yb³⁺ co-doped K_0.5Na_0.5NbO₃ ferroelectrics. After visible light irradiation, the ceramics exhibit a significant photochromism phenomenon turning from pale yellow to gray. The gray color can be eliminated via heat treatment or partly removed by an electric field stimulation. Upon 390-nm light irradiation for 4?min and thermal treatment at 200?°C for 5?min, the ceramics show a large modulation ratio (96%). In addition, the UC photoluminescence modulation can be in-situ operated by alternating the light irradiation and electric-field, showing an enhancing factor of 120% for the 390-nm light irradiated ceramics via applying an electric-field stimulation (12.5?kV/cm, 1?min). The developed ferroelectrics with large and reversible photoluminescence modulation through thermal stimulus and electric-field have great potential for digital memory and optoelectronic device applications.     

Dy/Sr-codoped (K0.5Na0.5)NbO3 multifunctional transparent-ferroelectric ceramics with adjustable white-light emission

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 (K_0.5Na_0.5)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.     

Reversible yellow-gray photochromism in potassium-sodium niobate-based transparent ceramics

Ferroelectric ceramics exhibiting photochromic behavior and reversible luminescence modulation are highly desirable for optoelectronic applications ranging from information storage, displays, anti-counterfeiting to photo-switching devices. Herein, Sm³⁺-doped lead-free 0.85(K_0.5Na_0.5)NbO₃-0.15SrZrO₃ (KNN-SZ: Sm³⁺) transparent ferroelectric ceramic featuring a typical photochromic phenomenon is designed and demonstrated. Upon alternate illumination and thermal stimulus (220 ℃ for 1 min), the ceramic exhibits reversible yellow-gray coloration. Furthermore, a maximum relative reflectivity variation of 29 % and a large luminescence quenching of 65.4 % with superior fatigue resistance were achieved in KNN-SZ: Sm³⁺. Various in-situ illuminations and thermal treatments in different ambient conditions were carried out to bring insight into the trapping and de-trapping processes involved in photochromic behavior. The KNN-SZ: Sm³⁺ photochromic ceramics have great prospect in optoelectronic devices expanding the applications of KNN-SZ ceramics into advanced multifunctional materials for devices integration beyond electrical energy storage, electrocaloric and piezoelectric effects.     

Developing "smart windows" for optical storage and temperature sensing based on KNN transparent ceramics

Smart windows have attracted considerable attention due to their wide applications in optical data storage, switchable sunroof and temperature sensing. The development strategy for smart windows is focused on performance design, enhancement and integration. However, developing integrated multi-functional smart windows in a single material remains a challenge. In this work, we have successfully prepared (K_0.5Na_0.5)_0.95Ba_0.04Er_0.01NbO₃ (4Ba-1Er-KNN) transparent ceramics for potential applications of temperature detection and optical information storage in smart windows. With alternating ultraviolet (UV) illumination and 300 °C thermal stimulation, the prepared 4Ba-1Er-KNN ceramics can not only achieve non-destructive luminescence readout, but also exhibits an ultra-high photochromic (PC) contrast with rapid response time of 1 s. Furthermore, based on the up-conversion (UC) photoluminescence (PL) intensity ratio of Er³⁺: ²H_11/2/⁴S_3/2 thermally coupled levels, excellent low-temperature sensing performance with the maximum relative sensitivity of 0.023 K⁻¹ at 213 K is obtained. The integration between UC PL, PC response and temperature sensing performance makes it possible to develop multi-functional smart windows.     

Photochromic effect of transparent lead-free ferroelectric KSr2Nb5O15 ceramics

Transparent KSr₂Nb₅O₁₅ (KSN) lead-free ferroelectric ceramics have been synthesized via modified pressureless sintering method. A significant photochromic effect was observed for the transparent KSN ceramics prepared without rare-earth dopant modification. The piezoelectric properties depend on the grain orientations were investigated. The optical transmittance of the KSN ceramics is greater than 40% in the wavelength range of 530–800 nm. After NUV irradiation, the absorbance was enhanced by more than 40% in a broad visible range (more than 79%). The absorbance returned to the initial value after a thermal bleaching process. The results of the cycling tests and response experiments showed the stability and saturation of the photochromic effect. In addition, the possible photochromic mechanism of the KSN ceramics is discussed and the photochromic centers are identified. This transparent KSN ceramics exhibits an obvious photochromic effect and is a potential candidate materials for optical data storage and information recording applications.     

Reversible upconversion switching for Ho/Yb codoped (K,Na)NbO3 ceramics with excellent luminescence readout capability

Luminescent readout capability for photochromic materials plays a critical role in 3D optical data storage applications, especially for inorganic photochromic materials in the solid‐state form. In our previous studies, we found that the luminescent readout capability can be improved using two or multiple‐photon excited luminescent mode (upconversion), which can effectively decrease the destruction degree of the excitation energies to the stored information during the luminescent “reading” process. However, the luminescent readout performance is unsatisfactory owing to the absence of nondestructive luminescence readout capability. Herein, we report a new solid‐state photochromic material with excellent upconversion readout capability: Ho³⁺/Yb³⁺ codoped (K,Na)NbO_3. Upon 407 nm light irradiation, the luminescent switching contrast (ΔR_t) is up to 78%. Particularly, the materials almost have no any re‐absorption to 980 nm light, exhibiting extremely low destruction to information recording points. The luminescent readout intensity retains 96% after constant 980 nm irradiation for 4 minutes at a high pumping power of 1W, which is superior to our previously reported results (Er/Yb codoped Bi_2.5Na_0.5Nb₂O₉ materials). This work would help to further develop new inorganic photochromic materials with high performance to satisfy the requirements for optical storage devices.     

INORGANIC NANOPARTICLES AS OPTICALLY EFFECTIVE ADDITIVES FOR POLYMERS

The transparency of polymer-particle composites can be markedly enhanced when nanoparticles are employed instead of larger particles, due to a reduction in light scattering. In addition, nanoparticles of metals (e.g., gold or silver) or semiconductors (e.g., TiO₂, ZnO, or PbS) can exhibit intrinsic optical properties that may be of interest per se or in combination with the enhanced transparency caused by the nanoparticles. For such reasons, inorganic nanoparticles have found special interest in studies devoted to optical properties in composites that look back to a long history. For instance, the size-dependent color of gold nanoparticles has been used to color glass for centuries. More recently, inorganic nanoparticles were investigated with regard to optical effects in polymeric nanocomposites such as very high or very low refractive index, reversible color switching in elastomers via swelling processes, dichroism in oriented polymers, reversible photochromic behavior, or UV absorption in visually transparent materials.     

Trap characteristics study of photorefractive polymer materials by thermal stimulated current spectroscopy

A thermal stimulated current (TSC) spectrometer was used to study the trap characteristics of photorefractive polymeric materials in this article. In addition to normal positive peaks due to segmental disorientation induced depolarization, there were negative peaks, even after a prior annealing treatment above T_g without electrical field to release the intrinsically trapped carriers in the film. The negative peaks of the photorefractive polymer containing the hole transport material probably resulted from the release of the trapped field-induced positive carriers during polarization. The negative peak enables trap characteristics to be distinguished from the segmental disorientation behavior. It also makes TSC a useful tool to study the trap characteristics of photorefractive polymers containing organic conducting materials with hole carrier domination in transportation. Incorporating different components into the film caused the change of trap behaviors. The charge transport material (CTM) incorporating in the nonlinear optical (NLO) material PMDA-DR19 reduced the trap depth and transformed the NLO material from nonphotoconductive to photoconductive. Adding charge generating material (CGM) generated an additional shallow trap by which the photogenerated electron-hole pairs were separated and the trapped holes were released more easily. The photorefractive composites with aromatic polyester hosts PMDA-DR19 and IPA-DR19 exhibited deeper trap depth and higher trap density than that with AA-DR19 host from aliphatic diacid. IPA-DR19/PVB/CTM, containing no carboxyl acid groups, possessed the same total trap density as PMDA-DR19/PVB/CTM, but the former exhibited a larger part of low energy traps than the latter did.     

光致变色玻璃在建筑中的节能性能评估

光致变色玻璃的透光率随光辐射强度的不同而变化,因此,光致变色玻璃可用于调控阳光进入建筑,是具有节能功效的智能玻璃。然而,目前光致变色玻璃在建筑中应用的研究较少,缺少科学评价其节能性能的方法。本文以制备的卤化银光致变色玻璃为研究对象,建立了光致变色玻璃节能性能简化模拟方法。利用DeST能耗软件研究了光致变色玻璃应用于不同建筑中的节能效果,计算和比较了两种变色特性的光致变色玻璃在不同建筑中的冷热负荷和照明能耗。研究结果显示:光致变色玻璃在建筑面积较大且窗墙比0.6以上的公共建筑中,全年节能率最高超过10%;在建筑面积和窗墙比较小的建筑中,其主要作用在于阻隔紫外线和防眩光。本文的方法和结果可为光致变色玻璃节能性能的研究提供参考,对光致变色玻璃的应用推广具有一定的促进作用。     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

螺噁嗪类光致变色化合物的制备及其性能初探

通过萘并噁嗪环上引入不同类型的取代基,合成了三种螺噁嗪光致变色化合物。研究了其光致变色性能和抗疲劳性能,结果表明,在紫外灯照射下由无色变为蓝色,这种变化是可逆的,并且具有较高的抗疲劳性。     

Anomalous upconversion behavior and high-temperature spectral properties of Yb/Ho-SiAlON ceramics

Traditionally, NaYF₄ and glass-based materials are considered the most efficient upconversion materials. However, those materials may show signs of thermal warping or risks of fracture during long-term service life in extreme environments. In contrast, SiAlON ceramics preserve their spectral and physical integrity during continuous use due to their ultra-low thermal expansion coefficient (～3.0 × 10^?6/K) even at extreme temperatures. Here, we investigate the upconversion photoluminescence properties of Ho and Yb co-doped SiAlON (Ho/Yb-SiAlON) ceramics, prepared by hot-press method, at room temperature and at high temperature (298–1023 K). At room temperature, Ho/Yb-SiAlON ceramics show intense red upconversion emission under 980 nm excitation. At the high-temperature range, the spectral shift is absent in Ho/Yb-SiAlON indicating that the SiAlON ceramics have high-temperature spectral stability, which may be attributed to the low thermal expansion coefficient of SiAlON ceramics. Ho and Yb concentration-dependent spectra show an anomalous upconversion emission behavior. It is found that a higher sensitizer and low activator concentration combination is not always an ideal choice for sensitized luminescence in SiAlON ceramics which is in stark contrast to the common understanding of sensitized luminescence. The mechanism involving the dominant cross-relaxation process has been proposed to explain the observed anomalous upconversion behavior.     

染料掺杂发光聚氨酯复合材料的制备及性能

为合理探讨使发光聚氨酯智能化的方法,本研究采用涂层整理的方式制备出具有热敏变色功能的柔性发光聚氨酯复合材料（LPC）。扫描电子显微镜（SEM）观察到材料表面粗糙不平;X射线衍射仪（XRD）分析表明涂层工艺和颜料的添加未影响材料中稀土发光材料的物相结构;反射率和发射光谱测试显示材料具有优异的热敏变色发光特性,标准光源下材料自身颜色可通过人体体温来改变（由红色变为白色）,经紫外-可见光源激发后,在黑暗环境中形成低温红光-高温白光的体系,充分展示其在智能可穿戴设备领域的应用潜力。     

光致变色化合物螺萘并吡喃的合成及光谱性能

以2-萘酚、苯肼和3-甲基-2-丁酮为原料,设计并合成了一种含萘环螺吡喃类光致变色化合物:1,3,3-三甲基吲哚啉螺萘并吡喃,通过1HNMR、IR和元素分析表征了它的分子结构,利用紫外光谱和荧光光谱对目标化合物的吸收光谱和光致发光光谱进行了研究,初步探索了目标产物的光致变色性能。吸收光谱结果表明,目标分子(闭环体)的二氯甲烷溶液(1×10-4mol/L)在可见光区基本无吸收而呈现无色,但经254 nm的紫外光照射后其开环体在480 nm处有较强的吸收而呈现红色(A=1.1),停止紫外光照射溶液恢复为无色,显示了良好的光致变色性能;发光光谱结果显示,目标分子经紫外光激发后其开环体在433 nm处有较强的蓝光发射。     

Photoluminescence,thermoluminescence and reversible photoluminescence modulation of multifunctional optical materials Pr3+ doped KxNa1-xNbO3 ferroelectric ceramics

It is highly significant to develop multifunctional optical materials to meet the huge demand of modern optics. Usually, it is difficult to realize multiple optical properties in one single material. In this study, we choose ferroelectric (K_xNa_1-x)NbO₃:Pr³⁺ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) as hosts, and the rare earth ions Pr³⁺ are doped in them. For the first time, the integration of photoluminescence, photochromism, luminescence modulation and thermoluminescence and has been achieved in the Pr³⁺ doped (K_xNa_1-x)NbO₃:Pr³⁺ ferroelectric ceramics. Upon 337- or 448-nm light irradiation, all samples show strong red emissions centered at 610 nm. The photochromic reaction increases with the increasing K⁺ content in the (K_xNa_1-x)NbO₃:Pr³⁺ ceramics. A strong photochromic reaction has been found in the (K_0.5Na_0.5)NbO₃:Pr³⁺ ceramics. Accordingly, a large and reversible photoluminescence modulation (ΔR_t = 50.71%) is achieved via altering 395-nm-light irradiation and 200 °C thermal stimulus. All the prepared ceramics show a visible thermoluminescence when stimulated at 200 °C. The mechanisms of luminescence modulation and thermoluminescence are discussed. Present study could provide a feasible paradigm to realize multiple optical properties in one single material.