Long-persistent Phosphorescence Research Articles

Polylactic acid film embedded with phosphor nanoparticles: Photochromic and afterglow biodegradable window and concrete

A smart window is a window made of a stimuli-responsive material whose transparency can be switched on and off. However, smart windows are often made of fragile, non-biodegradable and costly glass. Herein, this work presents the preparation of a transparent smart window from the environmentally-friendly polylactic acid (PLA) plastic. The plastic window was prepared by physically immobilizing nanoparticles of lanthanide-doped aluminate (NLdA; 79-112 nm) at different ratios into PLA bulk. The developed plastic showed afterglow emission, photochromism, superhydrophobicity, durability, UV shielding, rigidity, photostability, biodegradability, and excellent optical transmittance. NLdA was produced as nanoparticles to enhance NLdA dispersion in the plastic mass. NLdA must be uniformly disseminated in the PLA matrix without aggregation in order to provide transparent smart PLA window with long-persistent phosphorescence and photochromic properties. Different analytical methods were employed to determine the morphology, chemical composition, photoluminescence and coloration properties of smart films. There was an examination of the hardness characteristics. The transparent PLA window absorbed light at 365 nm and emitted at 435 nm and 517 nm, demonstrating reversible photochromism to green when irradiated with UV and greenish-yellow emission when exposed to darkness. There was a significant improvement in ultraviolet shielding and hydrophobicity upon increasing the phosphor content.

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

Smart windows with long-persistent phosphorescence, ultraviolet (UV) light 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 to produce transparent RPET/CNC substrates. Photoluminescence characteristics were also studied 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 colour under UV light to strong green and to greenish-yellow when it is dark, as proved by Commission Internationale de l'éclairage (CIE) laboratory colour 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 was evidence of improved UV shielding, photostability, and hydrophobic activity. In the presence of a low phosphor ratio, the luminescent RPET/CNC substrates showed quick and reversible fluorescence photochromic activity when exposed to UV radiation.

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. HIGHLIGHTS: Colorless photoluminescent smart nacre-like nanocomposites were prepared. Graphene oxide and polyester were mixed with phosphor nanoparticles at 25°C. Photostable long-persistent phosphorescence lighting was observed in the dark. Photochromic change to green emission was detected under ultraviolet light. The nacre-like composites exhibit improved hardness and hydrophobicity.

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 are usually produced from expensive and breakable glass materials. Herein, transparent smart window with long-persistent phosphorescence, high optical transmittance, ultraviolet (UV) protection, rigid, high photostability and durability, an d 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 abili ty to persist emitting light for extended time periods. The solid-state high temperature technique was used to prepare lanthanide-doped aluminate (LdA) micro-scale powder. Then, the top-down technique was applied to afford the corresponding LdAN. 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 microscopy (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 Fourier-transform infrared (FTIR) spectra), X-ray fluorescence (XRF) analysis, scanning electron microscopy (SEM), and energy-dispersion X-ray spectroscopy (EDX). 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 CIELab 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 anti-counterfeiting films and warning signs.

Preparation of flame-retardant, hydrophobic, ultraviolet protective, and luminescent transparent wood.

Transparent wood with multifunctional properties has recently attracted more attention as an efficient building product. Here, we describe the development of transparent wood with long-persistent phosphorescence, tough surface, high durability, photostability, and reversibility without fatigue, and with ultraviolet shielding, superhydrophobicity, and flame-retardant activity. This long-persistent phosphorescent, or glow-in-the-dark, smart wood exhibited an ability to continue emitting light for prolonged periods of time. The photoluminescent translucent wooden substrate was prepared by immobilizing lignin-modulated wooden bulk with an admixture of methylmethacrylate (MMA), ammonium polyphosphate (APP), and lanthanide-doped strontium aluminate (LSA; SrAl2 O4 :Eu2+ ,Dy3+ ) phosphor nanoparticles. The photoluminescent transparent wood displayed a colour switch from colourless to bright white beneath ultraviolet (UV) light and greenish-yellow in the dark as reported by Commission Internationale de l'Éclairage laboratory colorimetric space coordinates. The generated phosphorescent wooden substrates demonstrated an absorbance band at 365 nm and an emission band at 516 nm. The phosphorescent transparent wood was improved flame-retardant properties, ultraviolet shielding, and superhydrophobic properties, as well as a reversible long-persistent phosphorescent responsiveness to UV light without fatigue. The current approach demonstrated a potential large-scale production strategy for multifunctional transparent wooden substrates for a range of applications such as smart windows, gentle indoor and outdoor lighting, and safety directional signs in buildings.

Enhancement of Long-Persistent Phosphorescence by Solid-State Reaction and Mixing of Spectrally Different Phosphors.

Rare-earth-doped oxide-based phosphors have attracted great interest as light-emitting materials for technical applications and fundamental research because of their high brightness, tunable emission wavelength, and low toxicity, as well as chemical and thermal stability. The recent development of rare-earth-doped nanostructured materials showed improved phosphorescence characteristics, including afterglow and lifetime. However, the development of highly efficient phosphors remains challenging in terms of brightness and long persistence. Herein, novel protocols were developed for improving phosphorescence characteristics based on the energy transfer effect by chemical mixing of spectrally different phosphors. This protocol is based on the simple mixing method of different phosphors, which is totally different from the conventional methods but provides much brighter persistent phosphorescence. Simple chemical mixing methods significantly improved the afterglow intensity and lifetime of green and blue phosphors regardless of mixed time when subjected to a high-temperature solid-state reaction. In particular, chemical mixing after a high-temperature solid-state reaction enhanced the phosphorescence intensity more effectively than did chemical mixing before the reaction. We achieved increased luminescence of the phosphor, which is 10 times greater than that of the control sample, from all of the chemical mixing methods, which resulted in more efficient energy transfer than previously reported studies. Chemical mixing of three spectrally different phosphors was also performed to achieve multistep energy transfer for the first time, exhibiting a much higher afterglow intensity (∼2 times) than that of single-step energy transfer. This study provides a novel and simple method for the production of bright and long-persistent phosphors and thus expands their application range.

Long-persistent phosphorescence in Eu2+-doped calcium borate chloride for optical data storage

Yellow-emitting optical data storage phenomena were observed in a series of Ca2BO3Cl: Eu2+, Ln3+ (Ln = La, Ce, Pr, Sm, Gd, Tb, Ho, Tm, Yb, Lu) long-persistent phosphors. Eu2+ in Ca2BO3Cl could emit yellow light located at 580 nm ascribed to the 5d-4f transitions when optical data was being read out. As co-activators, Ln3+ had various effects in causing afterglow and changing trap concentration. Optical data storage phenomena occurred for each combination of Eu2+ and Ln3+ in calcium borate chloride host. Thereinto, prepared Ca2BO3Cl: Eu2+, Ce3+ phosphor presented a decent afterglow and optical storage property. Its afterglow decay time was more than 1 h at room temperature and had a bright yellow optical signal at 473 K Ca2BO3Cl: Eu2+, Ho3+ showed an optimum optical storage property, which remained bright yellow light even after 7 days of data storage. This outstanding optical data storage performance was mainly derived from Ho3+ increased the trap concentration of oxygen vacancies. The crystal structure, excitation and emission spectra, afterglow decay curves and thermoluminescence curves were measured and analyzed in all Eu2+ and Ln3+ doped Ca2BO3Cl samples. A simple optical data storage method was set up and effective optical signals were observed. Based on these results, detailed optical data storage processes and possible mechanism were studied and discussed.

Development of long-persistent photoluminescent epoxy resin immobilized with europium (II)-doped strontium aluminate.

A facile approach for possible industrial production of long-persistent phosphorescence, continuing to emitting light for a long time period, smart cobbles were developed toward photoluminescent hard surfaces. The inorganic strontium aluminium oxide pigment doped with rare earth elements was added to a synthetic organic epoxy in the presence of polyamine as a hardener to make a phosphor-loaded viscous fluid that can then be hardened in a few minutes. The transparency of the solid cobbles can be accomplished easily using homogeneous dispersion of the phosphor in the epoxy resin fluid before the addition of a hardener to avoid pigment aggregation. This pigment-epoxy formula can be easily applied industrially onto flagstones surfaces under ambient conditions. The photoluminescent cobblestones demonstrated an optimum excitation wavelength at 366 nm and an emission band at 521 nm with a long-persistent phosphorescence cobble surface. The development of a translucent white colour under normal daylight, bright green under ultraviolet (UV) irradiation, bright white colour after 30 sec in the dark, and phosphorescent green colour after 75 min in the dark was indicated using Commission Internationale de l'Eclairage (CIE) Laboratory coloration measurements. The luminescent hard composite cobble exhibited a highly durable and reversible long-persistent phosphorescence light. Photoluminescence, morphological, and hardness properties as well as the elemental composition of the prepared cobbles were explored.

Preparation and Luminescence Properties of Ba₅Si₈O21 Long Persistent Phosphors Doped with Rare-Earth Elements.

The phosphors of formula Ba5Si8O21:Eu2+,Dy3+ were synthesized and studied in order to improve their properties. Their synthesis conditions were evaluated as a function of precursors, crucible composition, flux agents, dopants and temperatures. The samples were characterised by means of a systematic investigation through elemental, kinetic, mineralogical (both qualitative and quantitative), and morphological analysis. This study allows for a careful evaluation of the parameters that influence the formation and properties of Ba5Si8O21:Eu2+,Dy3+ phosphors. As for the synthesis conditions, the use of Na2SiO3, BaCO3 and NH4Cl as precursors was very important to reduce the temperature and time of synthesis. The reducing atmosphere produced with purified coal was cheaper and gave results similar to the more traditional gas mixture (H2/N2). At the end of this study, a phosphor with improved long persistent phosphorescence (LPP) characteristics was obtained with Ba/Si = 0.7, Eu/Si = 2.8 × 10−3 and Dy/Si = 3.6 × 10−3 following a 6 h-synthesis in a quartz crucible.

Long-Persistent Circularly Polarized Phosphorescence from Chiral Organic Ionic Crystals.

Long-persistent circularly polarized phosphorescence (LPCPP) is achieved for the first time in chiral organic ionic crystals at room temperature. The co-crystal composed of terephtalic acid (TPA) and chiral α-phenylethyamines (PEAs) gave rise to LPCPP with lifetimes up to 862 ms and large dissymmetric factor (glum ). The hybridization of TPA with chiral PEAs allows circular polarization of the generated long-persistent phosphorescence. The observed mirror-image twisted molecular structures in the rigid lattices were responsible for the chiroptical activation of the generated long-persistent phosphorescence.

Aggregation-Induced Long-Lived Phosphorescence in Nonconjugated Polyurethane Derivatives at 77 K

Achieving long-persistent phosphorescence in polymers is a challenge even at low temperatures. In this work, long-persistent phosphorescence (>1 s) is observed in nonconjugated polyurethane derivatives at 77 K, which is among the longest reported phosphorescent lifetimes for an organic polymer. The mechanism for this unusual behavior has been shown by steady-state photophysical characterization and time-resolved emission spectra to arise from the formation of intra- and/or intermolecular carbonyl clusters at low temperature. The lifetime of long-persistent phosphorescence is increased by the introduction of an aromatic monomer into the nonconjugated polyurethane chains. This is attributed to intra- and/or intermolecular n−π* transitions from electron-rich carbonyl groups to the conjugated aromatic units, thereby enhancing the intersystem crossing rate. Coating an ultraviolet InGaAsN light-emitting diode with a polyurethane derivative as the emitter gives cryogenic afterglow with long-persistent phosphores...

Considerable improvement of Na2CaSn2Ge3O12:Eu3+ reddish orange long-persistent phosphorescence with Co-doping of Dy3+

A novel reddish orange long persistent phosphorescence was observed in Na2CaSn2Ge3O12:Eu3+ and Na2CaSn2Ge3O12:Eu3+,Dy3+ phosphors which were prepared using conventional solid-state method at 1250 °C in air. X-ray diffraction analyses demonstrate that all samples consist of Na2CaSn2Ge3O12 as the predominant phase. With the excitation of 318 nm, all the samples can emit reddish orange light, which is attributed to the 5D0→7F1 transition of Eu3+. The Dy3+ as co-dopants greatly prolong the phosphorescent persistence time of Na2CaSn2Ge3O12:Eu3+ phosphor. The persistent time of the persistence is 5 h, remarkable increased by 21-fold after the co-doping of 0.4 mol% Dy3+. The significant changes in the thermoluminescence curves demonstrated that the incorporation of Dy3+ into Na2CaSn2Ge3O12:Eu3+ not only enriched the types of traps, but also greatly increased the concentration of original traps (V″Ca,V″Na. It can be seen from the photoluminescence, long persistent phosphorescence and thermoluminescence spectra of all obtained samples that the optimal composition is Na2CaSn2Ge3O12:1.2%Eu3+,0.4%Dy3+. The possible mechanism of the reddish orange long persistent phosphorescence phosphor Na2CaSn2Ge3O12:Eu3+,Dy3+ is investigated.

The near-infrared long-persistent phosphorescence of Cr3+-activated non-gallate phosphor

Long persistent phosphors in the near-infrared (NIR) region have attracted much attention due to the potential application in in vivo imaging. A novel Cr3+-activated non-gallate phosphor was prepared by the Pechini method and characterized by photoluminescence, and long-lasting phosphorescence. Ca14Zn6Al10O35:Cr3+ phosphor gives a NIR long persistent luminescence (LPL) after the short UV-irradiation. The optimal concentration of Cr3+ for the LPP in non-gallate phosphor Ca14Zn6Al10O35:Cr3+ is experimentally about 0.5% and the afterglow time can last for 1h. Ca14Zn6Al10O35:Cr3+ is shown to be a new NIR persistent phosphor potentially suitable for in vivo imaging due to its 650–750nm emission range.

Cr3+:SrGa12O19: A Broadband Near‐Infrared Long‐Persistent Phosphor

Cr(3+)-doped SrGa12O19 is demonstrated to be a broadband near-infrared (650-950 nm) long-persistent phosphor whose luminescence can last for more than 2 h after ultraviolet irradiation is stopped. Detailed analysis of the photoluminescence and thermoluminescence spectra and of the persistent decay behavior of the Cr(3+)-doped SrGa12O19 samples indicate that the persistent energy transfer from the SrGa12O19 host to the Cr(3+) ions and the filling and release of electrons into and from the shallow and deep traps through the conduction band is responsible for the long-persistent phosphorescence.

Na2CaSn2Ge3O12: A Novel Host Lattice for Sm3+-Doped Long-Persistent Phosphorescence Materials Emitting Reddish Orange Light

A novel host lattice disodium calcium ditin(IV) trigermanium oxide Na2CaSn2Ge3O12 was utilized for synthesizing long-persistent phosphorescence materials for the first time. Reddish orange long-persistent phosphorescence was observed in Na2CaSn2Ge3O12:Sm(3+) phosphors with persistence time more than 4.8 h. The phosphors were synthesized by a conventional solid-state reaction pathway in air atmosphere. A predominant cubic phase of Na2CaSn2Ge3O12 was observed in all XRD patterns. Photoluminescence measurements indicated that the emission spectrum was composed of the peaks located at 566 (the strongest), 605, 664, and 724 nm. The results of the decay curves in terms of a biexponential model suggest that different defects appear in the crystal lattice. The defects acting as traps were investigated by thermoluminescence, which demonstrated that doping Sm(3+) ions into the Na2CaSn2Ge3O12 host has made the trap types abundant. Furthermore, the origin of the long-persistent phosphorescence has also been discussed. On the basis of the above results, Sm(3+)-doped Na2CaSn2Ge3O12 phosphors are considered to have potential practical applications.

Near infrared long-persistent phosphorescence in La_3Ga_5GeO_14:Cr^3+ phosphor

Near infrared (NIR; 660-1300 nm) long-persistent phosphorescence from Cr(3+) ions with persistence time of more than 1 hour was realized in La(3)Ga(5)GeO(14):Cr(3+) phosphor (with or without co-dopants such as Li(+), Zn(2+), Ca(2+), Mg(2+) and Dy(3+)). The NIR phosphorescence can be effectively achieved under UV illumination (~240-360 nm) but is barely achieved by blue light (~480 nm) irradiation, even though the blue light excitation are effective to the NIR fluorescence. The NIR phosphorescence mechanisms were discussed by measuring the irradiation energy dependence of the phosphorescence intensity.

Near infrared long-persistent phosphorescence in SrAl2O4:Eu2+,Dy3+,Er3+ phosphors based on persistent energy transfer

Eu 2 + , Dy3+, and Er3+ ions codoped SrAl2O4 phosphors with near infrared (NIR) (at 1530 nm) long-persistent phosphorescence were synthesized by a combustion method. The NIR phosphorescence emission was realized through a persistent energy transfer process from Eu2+ ions to Er3+ ions. Optimal Er3+ concentration for the maximum energy transfer efficiency was determined and NIR phosphorescence persisting for more than 10 min was achieved. A model of charge trapping and energy transfer process among Eu, Dy, and Er ions in SrAl2O4 host was proposed.

Preparation and luminescence properties of CaSnO3:Sm3+ phosphor emitting in the reddish orange region

A novel reddish orange light emitting phosphor, CaSnO3:Sm3+, is prepared via a two-step approach including the room temperature synthesis of CaSn(OH)6 precursor and then convert it into CaSnO3 by calcination and its optical properties are systematically investigated. X-ray diffraction, photoluminescence, long persistent phosphorescence and thermoluminescence spectra are used to characterize the synthesized phosphor. This phosphor is found to be well-crystallized by calcination at 750°C for 3h. Photoluminescence measurement indicates that Sm3+-doped CaSnO3 shows an overall reddish orange emission with a CIE values of x=0.57, y=0.37. After irradiation under the 254-nm UV light, the 4G5/2 to 6HJ (J=5/2,7/2,9/2,11/2) afterglow emissions of Sm3+ are obviously observed. Furthermore, the thermoluminescence and the possible mechanism for the long persistent phosphorescence (LPP) of the CaSnO3:Sm3+ phosphor is also discussed in this paper.

Excitation spectra of a long-persistent phosphor SrAl 2O 4 : Eu, Dy in vacuum ultraviolet region

This work has been carried out to understand the phosphorescence mechanism of the new-type long-persistent phosphor SrAl 2O 4 : Eu, Dy. Luminescence and excitation spectra were obtained by using vacuum ultraviolet (VUV) light as an excitation source. It is suggested that the 450 and 520-nm luminescence bands in SrAl 2O 4 : Eu, Dy excited with the VUV light may be attributed to the host sensitization. Creation spectrum of the long-persistent phosphorescence was firstly obtained in the VUV region by measuring the after-glow luminescence. A prominent peak was observed around 200 nm, namely in the low-energy tail of the fundamental absorption of SrAl 2O 4, indicating that the phosphorescence mechanism in SrAl 2O 4 : Eu, Dy may be closely related to the defect formation.