Development of Photoluminescent Translucent Wood toward Photochromic Smart Window Applications

Review of Photoluminescent-Photochromic Nanocomposites Containing Immobilized Inorganic Lanthanide-Doped Strontium Aluminate Nanoparticles

Synthesizing photoluminescent-photochromic nanocomposites is a broad and active research area with many articles published in recent years. Literature lacks a systematic review of nanocomposites that combine both photoluminescence and photochromism at once. This review article focused on synthesizing, properties, and selected applications of photoluminescent-photochromic nanocomposites. These two characteristics were brought about together in the nanocomposites by the immobilization of inorganic lanthanide-doped strontium aluminate nanoparticles (LSANs) in polymeric or ceramic matrices. The paper began by relating nanotechnology to composite materials and proceeded to discuss the concepts of luminescence and photochromism. Eventually, three main applications of such a class of nanocomposites were discussed in detail. The applications considered were smart windows, smart coatings, and anticounterfeiting. In all applications, the addition of the LSANs to the matrix material imparted magnificent enhancement of the photoluminescent and photochromic characteristics. Furthermore, the presence of LSANs in these nanocomposites caused remarkable enhancement in other properties such as mechanical properties, hydrophobicity, and protection against UV radiation.

Sustainable transparent wood focusing on lignin decolorization methods, polymer impregnation techniques and applications in functional buildings: A review

The utilization of transparent wood as a potential composite derived from wood offers numerous advantages, including exceptional mechanical properties, lightweight, low thermal conductivity and immense potential for multifunctionality. Additionally, transparent wood demonstrates commendable performance in both thermal insulation and light transmission management, contributing to the reduction of energy consumption. This makes it an attractive option for buildings and related engineering elements. However, despite the successes achieved to date, further improvement is still required in terms of overall sustainability and functionality to meet the demands of advanced applications. This paper provides a comprehensive summary of the transparent wood preparation process, highlighting the efforts made to improve sustainability through various approaches. These strategies encompass using environmental-friendly chemicals or methods for lignin decolorization, substituting petroleum-based polymers with bio-based alternatives, and increasing the cellulose content through densification techniques. In addition, this paper presents the functionalization aspects of transparent wood such as chromism, heat shielding properties, ultraviolet shielding properties, luminescence, and fire-resistance, as well as its building applications. Finally, the challenges currently encountered in the development and application of transparent wood are discussed with an emphasis on the necessity for additional exploration and advancement in this area.

Design and Synthesis of Multi-compartment Microcapsules via Pickering Emulsion Polymerization for Infrared Stealth and Adaptive Camouflage Applications

High-performance color-changing compounds, recognized as prominent smart materials, dynamically alter their color in response to external environmental stimuli. However, existing compounds exhibit limited responsiveness and color diversity, presenting challenges in the development of textiles responsive to multiple stimuli. This research introduces a novel design for dual-responsive color-changing microcapsules, employing a Pickering emulsion template method. The larger compartment encloses photosensitive dyes, whereas the smaller one contains thermochromic phase-change colorants. Adjusting the density of nanocapsules in the smaller compartment on the microcapsule surface enables a spectrum of colors, including red, yellow, blue, and green, triggered by light and heat. When incorporated into textiles, these microcapsules bestow adaptive color-changing attributes and infrared stealth capabilities onto the fabrics. Additionally, by modulating the color via surface micro/nanostructures, textile surfaces can exhibit hydrophobic and oleophobic properties. Such enhancements extend the textiles' potential applications in areas like anti-counterfeiting and military operations.

Ln-MOF in production of durable antimicrobial and UV-Protective fluorescent cotton fabric for potential application in military textiles

Industrialization of military textiles faces many challenges and some requirements such as durability, protection and suitability for hostile environment must be provided. Herein, fluorescent protective cotton with ultraviolet radiation (UVR)-protection and antimicrobial property was currently prepared via the immobilization of lanthanide-metal organic framework (Ln-MOF). Cotton fabrics were primarily activated via cationization process with 3-Chloro-2-hydroxypropyltrimethyl ammonium chloride to obtain the cationized cotton (Q-cotton). Subsequently, Ln-MOFs based on Europium (Eu) and Terbium (Tb) were separately immobilized within cotton and Q-cotton fabrics. The obtained Ln-MOF@fabrics showed good fluorescent character, while three and four emission bands were estimated for Eu-MOF@fabric and Tb-MOF@fabric, respectively, related to the electron transition from 5D0 to 7F0-4 in Eu3+ and from 5D4 to 7F3-6 in Tb3+. After Ln-MOF incorporation, UVR-protection factor (UPF) was significantly enlarged from 1.9 (insufficient UPF) to 22.1-25.6 (good UPF) without cationization and to 32.4-37.8 (very good UPF) for Q-cotton. Against three different pathogens (Escherichia coli, staphylococcus Aureus and Candida albicans), Ln-MOF@fabrics exhibited good microbial reduction of 68-79% and 81-91% in case of cotton and Q-cotton, respectively. The cationization improved the functionality and durability of fabrics, while the acquired functions were still existed even after 10 repetitive washings.

Smart Window with Reversible and Instantaneous Photoluminescence based on Microsphere Structure

A smart window that dynamically regulates light transmittance is crucial for modern life end-users and promising for on-demand optical devices. The advent of three-dimensional (3D) photonic crystal microspheres has enriched the functions of a smart window. However, the smart window formed by polymer microspheres encounters poor mechanical strength and microstructural defects. Herein, to solve this limitation, we report the microsphere-based smart window composed of tightly packed cross-linked polymer microspheres (as a precursor) containing organic photochromic dyes, followed by compression under a high elastic state. When excited under an ultraviolet supply, our smart window showed a rapid and reversible fluorescent photoluminescence without fatigue (50 cycles). Moreover, the bulk devices with a microsphere cross-linked network structure enable excellent mechanical strength (hardness reached 0.158 GPa) and visible-light transparency. Interestingly, a QR code can be recognized under visible light exposure but not under ultraviolet light exposure because of photoluminescence of the smart window. Our method generally provided a paradigm for various amorphous polymers, which can be regarded as a simple and effective approach to build a versatile strategy to introduce an ideal marketplace with economic and community benefits.

Coordination-driven in-situ controlled synthesis of cellulose-based fluorescent composite with tunable color for decoration, anti-counterfeiting, and accurate color recognition

Fluorescent composites have widespread applications in many aspects. Wood-derived cellulose is a renewable, easily processed and biodegradable, and cellulose-based fluorescent composites are highly favored for in different fields. However, the existing cellulose-based fluorescent composites still have many urgent problems to be solved, such as unstable luminescence properties and easy shedding of luminescent substances, and the development of their practical applications is still a formidable challenge. Herein, a green and mild strategy for the in-situ controllable synthesis of cellulose-based fluorescent composites membrane (CFM) was developed. Firstly, delignified wood (DW) was modified with citric acid, and then lanthanide ions were introduced on modified DW through coordinated covalent bonds. Additionally, the luminescence mechanism of CFM is proposed. CFMs show adjustable color for decorative and light conversion and can be accurately identified for data protection, which increases the high value-added of cellulose-based composites. The stable luminescent properties were maintained after sonication for 30 min or solvent immersion for three months. Therefore, this work presents a new approach for the synthesis of CFM, which provides an environment-friendly strategy for manufacturing cellulose-based fluorescent materials, which is significant for the subsequent development of environment-friendly composites for anti-counterfeiting and decorative applications.

Development of photoluminescent viscose fibers integrated with polymer containing lanthanide-doped phosphor

Smart clothing refers to textiles that can sense an external stimulus by changing their physical properties such as colorimetric and fluorescent fabrics. The pad-dry-curing coloration approach was used to apply a luminous and hydrophobic composite coating onto cellulose-based materials. This novel method includes incorporating phosphor nanoparticles made from lanthanide-doped strontium aluminum oxide (LSAO) into room temperature vulcanizing silicone rubber (RTV). The LSAO nano-sized particles (3-8 nm) must be mixed evenly throughout RTV without aggregation to allow for the formation of a colorless layer onto viscose surface. Pad-dry-curing the film onto viscose cloth worked well at room temperature. The contact angles of the luminous fibers enhanced from 138.6° to 158.2° as the LSAO ratio increased. The antimicrobial and ultraviolet (UV) protection of the LSAO-finished viscose were investigated. The transparent fluorescent film on viscose surface was excited at 367 nm to display an emission peak at 518 nm. According to CIE Lab coordinates and luminescence analyses, the fluorescent viscose fibers showed various colors, including white under visible light, intense green beneath UV device, and greenish-yellow under darkness. The comfort properties of the LSAO-finished viscose were assessed by measuring their bend length and permeability to air. Transmission electron microscopic analysis of LSAO nanoparticles was explored. Energy dispersive x-ray, x-ray fluorescence, and scanning electron microscopy were utilized to describe the spectroscopic outcomes of the treated textiles. The colorfastness of the LSAO-finished viscose fabrics was examined. The coated fabrics exhibited a non-fatigable reversible luminous photochromism in response to UV illumination. RESEARCH HIGHLIGHTS: Multifunctional LSAO@RTV nanocomposite was pad-dry-cured onto viscose textile. Photochromism to green under UV light and greenish-yellow in the dark was detected. Efficient antimicrobial, UV protective, and superhydrophobic activity were observed. The antimicrobial properties were maintained for 24 washing cycles. Pad-dry-cured viscose showed good comfortability and photostability.

Preparation of high-strength photochromic alginate fibers based on the study of flame-retardant properties

Color-changing fibers have attracted much attention for their wide applications in camouflage, security warnings, and anti-counterfeiting. The inorganic color-changing material tungsten trioxide (WO3) has been widely investigated for its good stability, controllability, and ease of synthesis. In this study, photochromic alginate fibers (WO3@Ca-Alg) were prepared by incorporating UV-responsive hybrid tungsten trioxide nanoparticles in the fiber production process. The prepared photochromic alginate fibers changed from white to dark blue after 30 min of UV irradiation and returned to their original color after 64 h. It can be seen that WO3@Ca-Alg has the advantage of long color duration. The strength of this fiber reached 2.61 cN/dtex and the limiting oxygen index (LOI) was 40.9 %, which indicates that the fiber exhibited mechanical resistance and flame-retardant properties. After the cross-linking of WO3@Ca-Alg by sodium tetraborate, a new core-shell structure was generated, which was able to encapsulate tungsten trioxide in it, thus reducing the amount of tungsten trioxide loss, and its salt and washing resistance was greatly improved. This photochromic alginate fiber can be mass produced and spun into yarn.

Fabrication of carbon dots-embedded luminescent transparent wood with ultraviolet blocking and thermal insulating capacities towards smart window application

To expand functions of transparent wood (TW) including fluorescence, ultraviolet blocking, heat preservation and insulation, we adopted carbon quantum dots (CQDs) to prepare luminescent transparent wood. CQDs with yellow/red fluorescence (YCD/RCD) were prepared by chitosan and o-phenylenediamine. Afterwards, Balsa woods were pretreated to obtain wood frameworks (DW/LW), which were further combined with epoxy resin for achieving transparent woods (DW-TW/LW-TW). Results showed LW retained more lignin, the LW-TW blocked more ultraviolet light, displaying the better visible transmission and mechanical strength than DW-TW. After adding YCD and RCD to LW-TW, the yellow and red fluorescence transparent woods with outstanding mechanical and ultraviolet blocking properties were prepared, especially the red fluorescence transparent wood (RTW). Specifically, the tensile strength and elongation at break of RTW reached up to 19.39 MPa and 5.35 %, respectively. Moreover, RTW could block 78.8 % of UV-B light and 78 % of UV-A light, respectively. Besides, RTW possessed excellent visible transmission (70.3 %) and UV blocking (88.87 %). Significantly, both RTW and YTW displayed outstanding water repellency, excellent durability, good thermal stability and insulation. Predictably, luminescent transparent woods certainly will enhance the adaptability of wood, and broaden its applications in green decoration, lighting setup, sensor and other fields.

Facile preparation of smart nanocomposite adhesive with superhydrophobicity and photoluminescence

Smart photoluminescent nanocomposite adhesive was developed toward simple commercial manufacturing of long-persistent luminescent and hydrophobic applications. The prepared photoluminescent glue was able to continue emitting light after turning the illumination source off even after being in the dark for up to 1.5 h. Lanthanide-doped strontium aluminum oxide (LSAO) nanoparticles (NPs) dispersed in liquid silicone rubber (SR) was prepared to function as nanocomposite glue for various surfaces. Using nano-scaled particles, LSAO was uniformly disseminated without agglomeration in the silicone rubber matrix, enabling the produced nanocomposite glue to transmit light. For the applied glues, there is an excitation peak determined at 365 nm, and an emission peak determined at 518 nm. Depending on the LSAO ratio, the photoluminescence spectra displayed either afterglow phosphorescence or fluorescence. Photochromism was monitored from transparent to greenish under UV irradiation and greenish-yellow in darkness. The glued samples benefit from enhanced superhydrophobicity and scratch resistance due to LSAO NPs embedded in the silicone rubber matrix. The glueed LSAO@SR nanocomposite showed high durability and resistance to light damages. This research established the feasibility of mass-producing smart glue for various uses such as building safety directed signs and smart windows.

Electrospun glass nanofibers to strengthen polycarbonate plastic glass toward photoluminescent smart materials

Electrospun glass nanofibers (GNFs) were used to strengthen polycarbonate (PC) to create long-persistent photoluminescent and fluorescent smart materials such as afterglow concrete and smart window. Physical integration of lanthanide-activated aluminate (LA) nanoparticles (NPs) yielded transparent GNFs@PC smart sheets. Spectral investigations utilizing photoluminescence and CIE Lab parameters were performed to confirm that the translucent appearance of GNFs@PC changed to green when exposed to UV light. This fluorescence activity was quickly reversible for the GNFs@PC hybrids with low concentrations of LANPs, which indicate fluorescence emission. Higher phosphor concentrations in GNFs@PC led to longer-lasting afterglow photoluminescence and slower reversibility. The GNFs@PC hybrids showed an emission band detected at 518 nm upon excitation at 368 nm. The morphological characteristics of LANPs and GNFs were analyzed by transmission electron microscopy (TEM), which revealed sizes of 11-26 nm and 250-300 nm, respectively. GNFs were prepared using electrospinning technology and then used as a roughening agent into PC sheets. Morphological characteristics of GNFs and GNFs@PC smart sheets were examined using energy-dispersive X-ray spectroscopy (EDXA), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The GNFs@PC smart sheets were shown to have enhanced scratch resistance in comparison to LANPs-free PC control sample. Increases in LANPs concentration enhanced both hydrophobicity and UV protection.

Development of hydrophobic, mechanically reliable, and glow-in-the-dark glue using Arabic gum

A smart nanocomposite adhesive was created to facilitate a simple production of long-persistent photoluminescent and hydrophobic commercial products. Even after being left in the dark for up to 90 min, the created photoluminescent adhesive agent continued to generate light. A surface-specific nanocomposite adhesive agent consisting of lanthanide-activated strontium aluminate (LSA) nanoparticles (NPs; 5-14 nm) immobilized in the environmentally friendly Arabic gum (AG) was developed. A light-transmitting nanocomposite adhesive agent was manufactured by dispersing LSA nanoparticles evenly across the AG matrix without agglomeration. An excitation peak at 365 nm and an emission wavelength at 519 nm were observed for the prepared adhesives at different concentrations of LSA NPs. The emission spectra showed either fluorescence or afterglow phosphorescence, depending on the LSA ratio. The photochromic transition from colourless to green beneath an ultraviolet (UV) lamp and greenish yellow in a dark room was tracked. The LSA NPs in the Arabic gum matrix imparted enhanced hydrophobicity and scratch resistance to the LSA@AG nanocomposite. The LSA@AG nanocomposite demonstrated excellent durability and photostability. This study confirmed that the mass production of smart adhesives for applications such as smart windows, smart packaging, and safety directional signs in buildings is possible.

Dual-mode security authentication of SrAl2 O4 :Eu,Dy phosphor encapsulated in electrospun cellulose acetate nanofibrous films

Photochromic inks have been an attractive authentication strategy to improve the anti-counterfeiting efficiency of commercial products. However, recent reports have shown significant disadvantages with photochromic inks, including poor durability and high cost. In this context, we developed novel photochromic nanofibres for advanced anti-counterfeiting applications. Lanthanide-doped strontium aluminate (LdSA) nanoparticles (NPs) were prepared and immobilized into electrospun cellulose acetate nanofibres (CANF). Authentication materials immobilized with inorganic photochromic agents can warranty durability and photostability. Therefore, the ultraviolet-stimulated photochromism of LdSA-encapsulated cellulose acetate nanofibres (LdSA@CANF) demonstrated high reversibility and photostability. A broad range of cellulose acetate nanofibres with unique emission characteristics was developed when applying different ratios of LdSA NPs. LdSA@CANF appeared colourless under visible daylight, whereas a green emission was monitored under ultraviolet-light illumination. The shape and chemical content of the photochromic fibrous films were examined using various analytical techniques. The mechanical characteristics of LdSA@CANF-coated paper were investigated. The emission wavelength was detected at 514 nm to designate green colour, whereas the excitation wavelength was detected at 369 nm to indicate transparency. The prepared cellulose acetate nanofibrous film can be described as an efficient strategy for the anti-counterfeiting of commercialized items.

Preparation of carbon dots-embedded fluorescent carboxymethyl cellulose hydrogel for anticounterfeiting applications

Fluorescent inks have been emerged as a desirable encoding technique to enhance anticounterfeiting printing of commercial goods. However, significant drawbacks with fluorescent inks, such as poor durability, low efficiency, and high cost. Herein, we describe the preparation of a self-healing authentication ink based on carboxymethyl cellulose (CMC) hydrogel immobilized with nitrogen-doped carbon dots (NCD) nanoparticles (NPs) for cutting-edge anticounterfeiting applications. Security inks that self-heal are very durable. Under ambient conditions, the prepared NCD@CMC hydrogel could self-heal with a high healing efficiency. It might stick to diverse surfaces such as plastic, glass and paper sheets. The self-healing composite ink demonstrated outstanding photostability under UV light. Straightforward and environmentally friendly method was applied on the agricultural waste of rice straw toward the production of NCD using hydrothermal carbonization in an aqueous medium, and in the presence of NH₄OH as an inexpensive passivating agent. The quantum yield (QY) for NCD reached 24.09 %. Various concentrations of NCD NPs were employed to produce self-healable nanocomposite inks with a variety of emission properties. Stamping homogeneous films onto paper surfaces produced a transparent layer. The CIE Lab and emission spectra of prints independently verified the capability of NCD nanocomposite inks to vary their color to blue under UV illumination. To measure the particle diameter of the prepared NCD, their morphological characteristics were examined by transmission electron microscopy (TEM) to indicate diameters of 10-25 nm. Utilizing various analytical techniques, the morphology and chemical composition of the fluorescent prints were examined. We examined the mechanical qualities of the stamped papers as well as the rheological characteristics of the ink hydrogel. Due to their colorless appearance, the excitation band of the printed films was peaked at 364 nm, while their emission was peaked at 465 nm. The current smart ink holds high potential for numerous applications like smart packaging and authentication, and shows great promise as a practical and mass production approach for easily creating anticounterfeiting stamps.

Development of Photoluminescent and Photochromic Polyester Nanocomposite Reinforced with Electrospun Glass Nanofibers

A polyester resin was strengthened with electrospun glass nanofibers to create long-lasting photochromic and photoluminescent products, such as smart windows and concrete, as well as anti-counterfeiting patterns. A transparent glass@polyester (GLS@PET) sheet was created by physically immobilizing lanthanide-doped aluminate (LA) nanoparticles (NPs). The spectral analysis using the CIE Lab and luminescence revealed that the transparent GLS@PET samples turned green under ultraviolet light and greenish-yellow in the dark. The detected photochromism can be quickly reversed in the photoluminescent GLS@PET hybrids at low concentrations of LANPs. Conversely, the GLS@PET substrates with the highest phosphor concentrations exhibited sustained luminosity with slow reversibility. Transmission electron microscopic analysis (TEM) and scanning electron microscopy (SEM) were utilized to examine the morphological features of lanthanide-doped aluminate nanoparticles (LANPs) and glass nanofibers to display diameters of 7-15 nm and 90-140 nm, respectively. SEM, energy-dispersive X-ray spectroscopy (EDXA), and X-ray fluorescence (XRF) were used to analyze the luminous GLS@PET substrates for their morphology and elemental composition. The glass nanofibers were reinforced into the polyester resin as a roughening agent to improve its mechanical properties. Scratch resistance was found to be significantly increased in the created photoluminescent GLS@PET substrates when compared with the LANPs-free substrate. When excited at 368 nm, the observed photoluminescence spectra showed an emission peak at 518 nm. The results demonstrated improved hydrophobicity and UV blocking properties in the luminescent colorless GLS@PET hybrids.

Preparation of Lighting in the Dark and Photochromic Electrospun Glass Nanofiber-Reinforced Epoxy Nanocomposites Immobilized with Alkaline Earth Aluminates

Alkaline earth aluminates (AEAs) as photoluminescent agents and silicon dioxide-based electrospun glass nanofibers with an average diameter of 150-450 nm as a roughening agent were prepared and applied to reinforce an epoxy resin toward the development of long-persistent photoluminescent and photochromic smart materials, such as smart windows and anticounterfeiting barcodes. With the physical immobilization of lanthanide-doped aluminate nanoparticles (NPs), a light-induced luminescent transparent glass@epoxy film was developed. The glass@epoxy samples were able to alter their color to green beneath ultraviolet rays and greenish-yellow in the dark, as explored by CIE Lab and luminescence spectral analyses. The morphology of the lanthanide-doped aluminate nanoparticles (43-98 nm) was examined by transmission electron microscopy (TEM). The morphologies and chemical composition of the luminescent glass@epoxy substrates were determined by different analytical techniques. The mechanical properties of the developed photoluminescent glass@epoxy substrates were inspected to show improved scratch resistance as compared to the AEA-free substrate. The photoluminescence spectra were measured to indicate the detection of two emission bands at 494 and 525 nm when excited at 365 nm. The photoluminescent glass@epoxy hybrids with lower AEA contents have showed fast reversibility of photochromism. On the other hand, the glass@epoxy substrates with higher phosphor contents underwent persistent luminescence. Results showed that the luminescent colorless glass@epoxy hybrids have enhanced superhydrophobicity and ultraviolet blocking.

Immobilization of Strontium Aluminate into Recycled Polycarbonate Plastics towards an Afterglow and Photochromic Smart Window

A transparent smart window made of recycled polycarbonate plastic (PCP) waste was prepared and immobilized with strontium aluminate phosphor nanoparticles (SAPN). It has afterglow emission, super-hydrophobicity, durability, photostability, good mechanical properties, ultraviolet protection, and high optical transmittance. To create an afterglow emission polycarbonate smart window (SAPN@PCP), recycled polycarbonate waste was integrated with various concentrations of SAPN (15-52 nm). SAP micro-scale powder was made using the solid-state high temperature method. The SAP nanoparticles were produced using the top-down method. To create a colorless plastic bulk, recycled polycarbonate waste was inserted into a hot bath. This colorless plastic was thoroughly combined with SAPN and cast to create an afterglow luminous smart window. To investigate its photoluminescence properties, spectrum profiles of excitation and emission were measured. According to the luminescence parameters, the phosphorescent colorless polycarbonate plates displayed a change in color to strong green under UV illumination and greenish-yellow in a dark box. The afterglow polycarbonate smart window displayed two emission peaks at 496 and 526 nm, and an absorption wavelength of 373 nm. Upon increasing the SAPN ratio, the hydrophobic activity, hardness, photostability, and UV protection were improved. Luminescent polycarbonate substrates with lower SAPN ratio demonstrated rapid and reversible fluorescence under UV light, while the higher SAPN content in the luminous polycarbonate substrates showed afterglow.

Preparation of photoluminescent nanocomposite ink for detection and mapping of fingermarks

Simple and efficient detection and mapping method based on a strong turn-on fluorescent pigment was developed for fingerprint analysis. We present a phosphor powder characterized by strong emission which is useful to achieve better fingerprint detection on multicolored or photoluminescent surfaces, such as currency notes characterized by optically changeable inks and highly fluorescent positions, because it offers better contrast and reduce the difficulty of background interference. Novel photochromic ink was prepared to establish a fingerprinted colorless film onto cellulose documents with green emission for anticounterfeiting applications as illustrated by photoluminescence spectra. Inorganic/organic nanoscale composite ink was prepared from rare-earth doped aluminate phosphor nanoparticles (PNPs; 27-49 nm) dispersed in a polyacrylic acid binding agent. PNPs were dispersed efficiently in polyacrylic acid to generate a colorless mark. The produced photochromic inks were spray-coated onto off-white paper sheets enclosing invisible fingermarks, and then exposed to thermofixation. Photochromic film was detected on paper surface presenting a transparent appearance under visible daylight and switchable to green under UV light. The CIE Lab parameters and photoluminescence spectra were studied under visible light and ultraviolet irradiation. The fingerprinted sheets showed fluorescence band at 517 nm upon excitation at 366 nm, showing a bathochromic shift and reversible photochromism without fatigue. The morphologies of pigment phosphor particles and fingerprinted sheets were inspected. The rheological properties of ink and mechanical behavior of the fingerprinted paper samples were explored. HIGHLIGHTS: Novel smart ink with alkaline-earth aluminate and polyacrylic acid was developed. Dual-mode fluorescent photochromism was presented for latent fingerprint analysis. Off-white fingerprinted films under daylight showed color change to green under UV. Fluorescence band monitored at 517 nm upon excitation at 366 nm. Fluorescent fingermark on paper sheets demonstrated good photostability.

Preparation of photoluminescent and anticorrosive epoxy paints immobilized with nanoscale graphene from sugarcane bagasse agricultural waste

Sugarcane bagasse agricultural waste has been one of the most common solid pollutants worldwide. Thus, introducing a simple method to convert sugarcane bagasse into value-added materials has been highly significant. Herein, we develop a simple and green strategy to reprocess sugarcane bagasse as a starting material for the preparation of graphene oxide nanosheets toward the preparation of novel photoluminescent, hydrophobic, and anticorrosive epoxy nanocomposite coatings integrated with lanthanide-doped aluminate nanoparticles. Environmentally friendly graphene oxide (GO) nanostructures were provided by a single-step preparation procedure from sugarcane bagasse (SCB) agricultural waste using ferrocene-based oxidation under muffled conditions. The oxidized SCB nanostructures were applied as a drier, anticorrosion, and crosslinking agent for epoxy coatings. Different concentrations of pigment phosphor were applied onto the epoxy coating. The generated epoxy-graphene-aluminate (EGA) paints were then coated onto mild steel. The hydrophobic properties and hardness as well as resistance to scratch of the EGA paints were examined. The transparency and colorimetric screening of the EGA nanocomposite paints were determined by the absorption spectral analysis and CIE Lab parameters. The luminescent translucent paints demonstrated a bright green emission at 520 nm when excited at 372 nm. The anticorrosion properties of the painted steel submerged in NaCl_(aq) were inspected by the electrochemical impedance spectral (EIS) method. The EGA paints with phosphor (11% w/w) exhibited the most distinct anti-corrosion properties and long-persistent luminescence. The produced paints displayed high durability and photostability.

Optical properties of novel luminescent nacre-like epoxy/graphene nanocomposite coating integrated with lanthanide-activated aluminate nanoparticles

Nacre structure has aragonite polygonal tablets, tessellated to generate separate layers, and exhibits adjacent layers and tablets within a layer bonded by a biopolymer. Herein, we report the development of nacre-like organic/inorganic hybrid nanocomposite coating consisting of epoxy tablets as well as rare-earth activated aluminate and graphene oxide tablet/tablet interfaces. The lanthanide-activated aluminate was prepared by the high temperature solid-state approach followed by the top-down technology to provide the phosphor nanoparticles (PNPs). Graphene oxide nanosheets were prepared from graphite. The prepared epoxy/graphene/phosphor nanocomposites were applied onto mild steel. Covalent bonds were formed between epoxy polymer chains resin and graphene oxide nanosheets. Those interface interactions results in tough surface, high tensile strength, and excellent durability. The usage of phosphor in the nanoparticle form guaranteed no agglomerations were produced throughout the hardening procedure by allowing better distribution of PNPs in the nacre-like matrix. The generated nacre-like substrates displayed reversible fluorescence. The excitation of the white colored nacre-like coats at 367 nm results in a green emission band at 518 nm as designated by CIE Lab and photoluminescence spectra. Various analysis methods were utilized to inspect the surface structure and elemental composition of the nacre-like coats. An improved hydrophobicity and mechanical characteristics were detected with increasing the phosphor concentration. Due to the astonishing characteristics of the prepared nacre-like composite paint, both ceramics and metals can benefit from the current simple strategy.

Photoluminescent and photochromic smart window from recycled polyester reinforced with cellulose nanocrystals

Smart windows with long-persistent phosphorescence, UV protection, high transparency, and high rigidity were developed by easily immobilizing varying ratios of lanthanide-activated aluminate phosphor nanoscale particles within a composite of recycled polyester/cellulose nanocrystals (RPET/CNC). Cellulose nanocrystals were prepared from rice straw waste. Cellulose nanocrystals were used at low concentration as both crosslinker and drier to improve both transparency and hardness. The phosphor nanoscale particles must be distributed into the recycled polyester/cellulose nanocrystals composite bulk without agglomeration in order to produce transparent RPET/CNC substrates. Photoluminescence characteristics were also studied by using spectroscopic profiles of excitation/emission and decay/lifetime. The hardness efficiency was also examined. This transparent recycled polyester waste/cellulose nanocrystals nanocomposite smart window has been shown to change color under UV light to strong green and to greenish-yellow when it is dark, as proved by CIE Lab color parameters. It was found that the afterglow RPET/CNC smart window had phosphorescence intensities of 428, 493 and 523 nm upon excitation at 368 nm. There were evidences of improved UV shielding, photostability, and hydrophobic activity. In the presence of low phosphor ratio, the luminescent RPET/CNC substrates showed quick and reversible fluorescent photochromic activity when exposed to UV radiation.

Color-switchable and photoluminescent poly (vinyl chloride) for multifunctional smart applications

Recycled poly (vinyl chloride) (PVC) waste was used to prepare transparent material with long-lasting phosphorescence, photochromic activity, hydrophobicity, strong optical transmission, ultraviolet (UV) protection, and stiffness. Lanthanide-activated aluminate (LaA) microparticles were prepared via the high temperature solid state procedure, which were subjected to the top-down grinding technology to afford LaA nanoparticles (LaAN). Laminated poly (vinyl chloride) bottles were shredded into a transparent plastic matrix, which was combined with LaAN and drop-casted to produce smart materials for a variety of applications. Smart window and photochromic film for smart packaging can be made from recycled poly (vinyl chloride) waste by immobilizing it with various ratios of LaAN. Long-lasting phosphorescent translucent poly (vinyl chloride) smart window and films need LaAN to be evenly dispersed in PVC without clumping. Different analytical methods were employed to assess the materials' morphological structure and chemical composition. Photoluminescence and decay spectra were all employed to investigate the luminescence characteristics. In addition, the mechanical performance was studied. According to CIE Lab (Commission Internationale de L'éclairage) color measurements, this transparent PVC smart material becomes a bright green under UV rays and turns a greenish-yellow in the dark. The PVC luminescence was observed to exhibit an apparent emission bands at 429 and 513 nm when excited at 367 nm. Improvements have been monitored in the UV shielding and hydrophobicity with increasing the phosphor concentration. LaAN-immobilized PVC exhibited reversible photochromism. The present approach can be applied for a variety of applications, such as anticounterfeiting films for smart packaging, smart window, and warning lightening marks.

Development of functional glow-in-the-dark photoluminescence linen fabrics with ultraviolet sensing and shielding

Linen fibres were coated with a glow-in-the-dark photoluminescence, flame-retarding, and hydrophobic smart nanocomposite using the pad-dry-curing process. Ecologically friendly ammonium polyphosphate and lanthanide-activated strontium aluminium oxide (LSAO) nanoparticles were immobilized into linen fabric using eco-friendly room-temperature-vulcanizing silicone rubber. Different analytical techniques were used to examine the morphological characteristics and elemental compositions of LSAO nanoparticles and treated linen textiles. The self-extinguishing properties of the treated linen textiles were tested for their fire resistance. After 24 washing cycles, the coated linen samples retained their flame-retarding properties. The treated linen's superhydrophobicity rose in direct proportion to the LSAO concentration. After being excited at 365 nm, the colourless luminescent film that was coated on linen surface gave out an emission wavelength of 519 nm. The photoluminescent linen was monitored to create a range of different colours, including off-white in daytime light and green under ultraviolet (UV) light radiation, according to the Commission Internationale de l'éclairage laboratory colorimetric coordinates and photoluminescence spectra. Emission, excitation, and lifetime spectral analysis of the treated linen revealed persistent phosphorescence. For mechanical and comfort evaluation, the coated linen textiles' bending length and air permeability were assessed. Good UV light shielding and enhanced antibacterial activity were detected in the treated linens.

Development of photoluminescent artificial nacre-like nanocomposite from polyester resin and graphene oxide

Long-lasting phosphorescent nacre-like material was simply prepared from a nanocomposite of inorganic and organic materials. Low molecular weight unsaturated polyester (PET), graphene oxide (GO), and nanoparticles of rare-earth activated aluminate pigment were used in the preparation process of an organic/inorganic hybrid nanocomposite. Using methylethylketone peroxide (MEKP) as a hardener, we were able to develop a fluid solution that hardens within minutes at room temperature. Covalent and hydrogen bonds were introduced between the polyester resin and graphene oxide nanosheets. The interface interactions of those bonds resulted in toughness, excellent tensile strength, and high durability. The produced nacre substrates demonstrated long-persistent and reversible luminescence. The excitation of the produced nacre substrates at 365 nm resulted in a 524 nm emission. After being exposed to UV light, the photoluminescent nacre substrates became green. The increased superhydrophobic activity of the produced nacre substrates was achieved without affecting their physico-mechanical properties.

Simple preparation of novel photochromic polyvinyl alcohol/carboxymethyl cellulose security barcode incorporated with lanthanide-doped aluminate for anticounterfeiting applications

Forgery and low-quality products pose a danger to the society. Therefore, there are increasing demands for the production of easy to recognize and difficult to copy anti-counterfeiting materials. Products with smart photochromic and fluorescent properties can change color and emission spectra responding to a light source. In this context, we devised a straightforward preparation of luminescent polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) nanocomposite to function as a transparent labeling film. The lanthanide-doped aluminate (LdA) was prepared in the nanoparticle form to indicate diameters of 35-115 nm. Different ratios of the lanthanide-doped aluminate (LdA) were physically dispersed in the PVA/CMC nanocomposite label film to provide photochromic, ultraviolet protection, antimicrobial activity and hydrophobic properties. Fluorescence peaks were detected at 365 and 519 nm to indicate a color change to green. As a result of increasing the phosphor ratio, improved superhydrophobic activity was achieved as the contact angle increased from 126.1° to 146.0° without affecting the film original physical and mechanical properties. Both UV protection and antibacterial activity were also investigated. The films showed quick and reversible photochromic response without fatigue. The current strategy reported the development of photochromic smart label that is transparent, cost-effective and flexible. As a result, numerous anticounterfeiting products can benefit from the current label for a better market. LdA-loaded PVA/CMC films demonstrated antibacterial activity between poor, good, very good and outstanding as the percentage of LdA in the film matrix increased. The current film can be applied as a transparent photochromic security barcode for anticounterfeiting applications and smart packaging.

Simple Preparation of Photoluminescent and Color-Tunable Polyester Resin Blended with Alkaline-Earth-Activated Aluminate Nanoparticles

A simple inorganic/organic nanocomposite was used to generate long-lasting phosphorescent pebbles for easy commercial manufacturing of smart products. An organic/inorganic nanocomposite was made from low-molecular-weight unsaturated polyester and rare-earth-activated strontium aluminum oxide nanoparticles doped with europium and dysprosium. The polyester resin was mixed with phosphorescent strontium aluminate oxide nanoparticles and methylethyl ketone peroxide as a cross-linking agent to create a viscous mixture that can be hardened in a few minutes at room temperature. Before adding the hardener catalyst, the phosphorescent strontium aluminate nanoparticles were dispersed throughout the polyester resin in a homogeneous manner to ensure that the pigment did not accumulate. Long-lasting, reversible luminescence was shown by the photoluminescent substrates. The emission was reported at 515 nm upon exciting the pebble at 365 nm. In normal visible light, both blank and luminescent pebbles had a translucent appearance. As a result of UV irradiation, the photoluminescent pebbles produced an intense green color. The three-dimensional CIE Lab (International Commission on Illumination) color coordinates and luminescence spectra were used to investigate the color changing characteristics. Photophysical characteristics, including excitation, emission, and lifetime, were also investigated. Scanning electron microscopy, wavelength-dispersive X-ray fluorescence spectroscopy, and energy-dispersive X-ray analysis were employed to report the surface morphologies and elemental content. Without impairing the pebbles' original physico-mechanical characteristics, the pebbles showed improved superhydrophobic activity. The current simple colorless long-lasting phosphorescent nanocomposite can be applied to a variety of surfaces, like ceramics, glassware, tiles, and metals.

Reversible Photo-, Thermal-, and pH-Responsive Functionalized Wood with Fluorescence Emission

A reversible photo-, thermal-, and pH-responsive high-performance functional wood with fluorescence has been prepared. The properties, structure, multi-response, fluorescence, water resistance, and corrosion resistance of original wood (ORW) and functional wood (FUW) were investigated with an X-ray photoelectron spectroscopy (XPS) spectrometer, a Fourier-transform infrared (FTIR) spectrometer, a N₂ adsorption–desorption analyzer, an atomic force microscope (AFM), tensile tests, a scanning electron microscope (SEM), an ultraviolet–visible (UV–Vis) spectrophotometer, a fluorescence spectrometer, the equilibrium swelling ratio (ESR), and corrosion tests. The results of XPS, FTIR, N₂ adsorption–desorption, and AFM exhibited that FUW was successfully prepared. Additionally, the results of the tensile test and SEM revealed that FUW had better mechanical properties than ORW, due to the filling of epoxy resin in the pores of the wood. Moreover, the UV–Vis and fluorescence spectra demonstrated that the introduction of epoxy resin induced multi-response and fluorescence functions to FUW. Furthermore, the data of ESR and corrosion test showed that the introduction of epoxy resin greatly improved the water and corrosion resistance of wood. This study provides ideas and methods for preparing novel high-performance multi-response FUW.

Immobilization of lanthanide doped aluminate phosphor onto recycled polyester toward the development of long-persistent photoluminescence smart window

Smart window can be defined as switchable material whose light transmission is altered upon exposure to light, voltage, or heat. However, smart windows usually produced from expensive and breakable glass materials. Herein, transparent smart window with long-persistent phosphorescence, high optical transmittance, ultraviolet protection, rigid, high photostability and durability, and superhydrophobicity was developed from recycled polyester (PET). Recycled polyester waste (RBW) was simply immobilized with different ratios of lanthanide-doped aluminate nanoparticles (LdAN) to provide a long-persistent phosphorescent polyester smart window (LdAN@PET) with an ability to persist emitting light for extended time periods. The solid-state high temperature technique was used to prepare LdA micro-scale powder. Then, the top-down technique was applied to afford the corresponding LdA nanoparticles. Recycled shredded recycled polyester bottles were charged into a hot bath to provide a clear plastic shred bulk, which was then well-mixed with LdAN and drop-casted to provide long-persistent luminescent smart window. In order to improve the phosphor dispersion in the PET bulk, LdAN was synthesized in the nanoparticle form which was characterized utilizing transmission electron microscope (TEM). For better preparation of translucent smart window of long-persistent phosphorescent polyester, LdAN must be homogeneously dispersed in the PET matrix without agglomeration. The morphology and chemical composition were studied by infrared spectra (FT-IR), X-ray fluorescent (XRF) analysis, scanning electron microscopy (SEM), and energy-dispersion X-ray analyzer (EDS). In addition, spectral profiles of excitation and emission, and decay and lifetime were used to better understand the photoluminescence properties. The hardness properties were also investigated. The developed phosphorescent transparent polyester smart window demonstrated a color switch to intense green underneath UV irradiation and greenish-yellow under darkness as verified by CIE Lab color parameters. The afterglow polyester smart window showed an absorption wavelength at 365 nm and two phosphorescence intensities at 442 and 512 nm. An enhanced UV protection, photostability and hydrophobic activity were detected. The luminescent polyester substrates with lower LdAN ratios demonstrated rapid and reversible fluorescent photochromic activity beneath the UV light. The luminescent polyester substrates with higher LdAN contents displayed long-persistent phosphorescence afterglow. The current strategy can be simply applied for the production of smart windows, low thickness anticounterfeiting films and warning signs.

Development of silica-coated rare-earth doped strontium aluminate toward superhydrophobic, anti-corrosive and long-persistent photoluminescent epoxy coating

Long-persistent phosphorescent smart paints have the ability to continue glowing in the dark for a prolonged time period to function as energy-saving products. Herein, new epoxy/silica nanocomposite paints were prepared with different concentrations of lanthanide-doped aluminate nanoparticles (LAN; SrAl₂ O₄ : Eu²⁺ , Dy³⁺ ). The LAN pigment was firstly coated with SiO₂ utilizing the heterogeneous precipitation technique to provide LAN-encapsulated between SiO₂ nanoparticles (LAN@SiO₂ ). The epoxy/silica/lanthanide-doped aluminate nanoparticles (ESLAN) nanocomposite paints were coated on steel. The prepared ESLAN paints were studied by transmission electron microscope (TEM), infrared spectra (FTIR), scanning electron microscope (SEM), X-ray fluorescence analysis (XRF), and energy-dispersive X-ray spectra (EDS). The transparency and coloration properties of the nanocomposite coated films were explored by CIE Lab parameters and photoluminescence spectra. The ultraviolet-induced luminescence properties of the transparent coated films demonstrated greenish phosphorescence at 518 nm upon excitation at 368 nm. Both hardness and hydrophobic activities were investigated. The anticorrosion activity of the nanocomposite films coated onto mild steel substrates immersed in NaCl_(aq) (3.5%) was studied by the electrochemical impedance spectral (EIS) analysis. The silica-containing coatings were monitored to exhibit anticorrosion properties. Additionally, the nanocomposite films with LAN@SiO₂ (25%) exhibited the optimized long-lasting luminescence properties in the dark for 90 minutes. The nanocomposite films showed highly reversible and durable long-lived phosphorescence.

Production of photoluminescent transparent poly(methyl methacrylate) for smart windows

Photochromic and long-lasting photoluminescent transparent, rigid, ultraviolet (UV) protective and superhydrophobic poly(methyl methacrylate) (PMMA) plastic able to switch colour beneath UV irradiation was developed. Photoluminescent transparent PMMA plastic was prepared by the simple polymerization process of methyl methacrylate immobilized with alkaline earth aluminate (AEA) nanoparticles. These colourless PMMA plastic substrates showed a colour switch to greenish underneath UV light as proved using CIELAB screening. The morphology of AEA was evaluated using transmission electron microscopy. Conversely, transparent PMMA samples were evaluated using energy-dispersive X-ray spectra, scanning electron microscope, X-ray fluorescence spectroscopy and for hardness properties. Additionally, the photoluminescence properties were explored by studying excitation and emission spectra. The produced luminescence colourless PMMA plastic substrates displayed excitation band at 370 nm, and three emission peaks at 433, 494 and 513 nm. Photoluminescent PMMA with lower contents of AEA showed fast and reversible photochromism under UV light, while PMMA samples with higher contents of AEA showed long-lasting luminescence such as a flashlight with the ability to replace electric power. The findings showed that the produced photoluminescence colourless PMMA plastic substrates exhibited enhanced UV shielding and superhydrophobicity.

Facile production of smart superhydrophobic nanocomposite for wood coating towards long-lasting glow-in-the-dark photoluminescence

A smart photoluminescent nanocomposite surface coating was prepared for simple industrial production of long-persisting phosphorescence and superhydrophobic wood. The photoluminescent nanocomposite coatings were capable of continuing to emit light in the dark for prolonged time periods that could reach 1.5 h. Lanthanide-doped aluminium strontium oxide (LASO) nanoparticles at different ratios were immobilized in polystyrene (PS) and developed as a nanocomposite coating for wood substrates. To produce transparency in the prepared nanocomposite coating, LASO was efficiently dispersed in the form of nanoscaled particles to ensure homogeneous dispersion without agglomeration in the PS matrix. The coated wood showed an absorption band at 374 nm and two emission bands at 434 nm and 518 nm. The luminescence spectra showed both long-persisting phosphorescence as well as photochromic fluorescence relying on the LASO ratio. The improved superhydrophobicity and resistance to scratching of the coated wood could be attributed to the LASO NPs incorporated in the polystyrene matrix. Compared with the uncoated wood substrate, the coated LASO-PS nanocomposite film also displayed photostability and high durability. The current study demonstrated the potential high-scale manufacturing of smart wood for some applications such as safety directional signs in buildings, household products, and smart windows.