Persistent phosphors for luminous paints: A review

The article briefly reports the fundamental scientific principles and landmarks in the field of luminescence and further enlightens the importance of persistent phosphor that is now widely used in luminous paints. Its main focus is on phosphorescence that makes use of lanthanides that have gained paramount importance in various cross-sections of luminescent applications. Both inorganic and organic afterglow materials, synthesis and characterization along with skilled researchers' essential updates on emerging trends and efforts are elucidated at length. It exclusively reviews the red/green/blue organic/inorganic/hybrid phosphorescent materials and the latest advances in the development of novel long afterglow materials that can accelerate the green technology in the world of luminescence.     

Changes in photosynthetic electron transfer and state transitions in an herbicide-resistant D1 mutant from soybean cell cultures

Anomalies in photosynthetic activity of the soybean cell line STR7, carrying a single mutation (S268P) in the chloroplastic gene psbA that codes for the D1 protein of the photosystem II, have been examined using different spectroscopic techniques. Thermoluminescence emission experiments have shown important differences between STR7 mutant and wild type cells. The afterglow band induced by both white light flashes and far-red continuous illumination was downshifted by about 4 °C and the Q band was upshifted by 5 °C. High temperature thermoluminescence measurements suggested a higher level of lipid peroxidation in mutant thylakoid membranes. In addition, the reduction rate of P700⁺ was significantly accelerated in STR7 suggesting that the mutation led to an activation of the photosystem I cyclic electron flow. Modulated fluorescence measurements performed at room temperature as well as fluorescence emission spectra at 77 K revealed that the STR7 mutant is defective in state transitions. Here, we discuss the hypothesis that activation of the cyclic electron flow in STR7 cells may be a mechanism to compensate the reduced activity of photosystem II caused by the mutation. We also propose that the impaired state transitions in the STR7 cells may be due to alterations in thylakoid membrane properties induced by a low content of unsaturated lipids.     

The long rod-shaped Sr2MgSi2O7:Eu2+,Dy3+ with ultrahigh afterglow performance

The afterglow properties of long afterglow luminescent materials are greatly affected by their defects, which are distributed on the grain surface. Increasing the exposed surface area is an important method to improve the afterglow performance. In this research, long rod-shaped long afterglow materials Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were prepared using the hydrothermal-coprecipitation method. When the reaction time reached 96 h, the length of the afterglow materials could grow to 2 mm, and the sintering temperature was just 1150°C. The emission spectra of all obtained samples upon excitation at 397 nm had a maximum of 465 nm, which belonged to the representative transition of Eu²⁺. The initial brightness was 1.35 cd/m². The afterglow time could reach 19 h, giving a good afterglow performance. The research on this kind of material has essential significance in the exploration of luminescence mechanisms and their applications.     

Photoluminescent polymer-based smart window reinforced with electrospun glass nanofibres

Poly(vinyl chloride) (PVC) was reinforced with electrospun glass nanofibres (EGN) to develop photochromic and afterglow materials such as smart windows and anti-counterfeiting prints. A colourless electrospun glass nanofibres@poly(vinyl chloride) (EGN@PVC) sheet was prepared by physical integration of lanthanide-doped aluminate nanoparticles (LANP). The low concentrations of LANP in the photochromic and photoluminescent EGN@PVC hybrids displayed fluorescence emission with instant reversibility. EGN@PVC with the highest phosphor concentrations showed persistent phosphorescence emission with slow reversibility. Based on the results of the Commission Internationale de l'éclairage Laboratory and luminescence spectroscopy, the translucent EGN@PVC samples became green in the presence of ultraviolet illumination and greenish-yellow in the absence of light. According to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses, the morphological study of EGN and LANP showed diameters of 75–95 and 11–19 nm, respectively. The morphology of the EGN@PVC substrates was studied using SEM, X-ray fluorescence, and energy-dispersive X-ray spectroscopy. The mechanical characteristics of PVC were enhanced by reinforcement with EGN as a roughening agent. When comparing the scratching resistance of LANP-free substrate to photoluminescent EGN@PVC substrates, it was observed that the latter was much superior. The photoluminescence spectra were reported to have an emission peak at 519 nm when excited at 365 nm. These findings demonstrated that the luminous transparent EGN@PVC composites had improved superhydrophobic and UV-blocking characteristics.     

Preparation and characterization of selenium‐decorated graphene quantum dots with high afterglow for application in photodynamic therapy

Graphene quantum dots (GQDs) was synthesized using a simple, rapid and affordable method and decorated with selenium at different molar ratios for the first time to obtain an efficient sample for use in photodynamic therapy. Surface modification of GQDs was carried out using polyethylene glycol (PEG) for conjugation with protoporphyrin IX (PpIX). Synthesized GQDs (Se: 0.3%) at 180°C had an emission spectrum that fairly coincided with the absorption profile of PpIX. A relative decrease of about 62.48% in the emission intensity of anthracene was recorded under illumination with UVC light in the presence of GQDs (Se: 0.3%) and the reduction for clung GQDs (Se: 0.3%) and PpIX during 90 min was about 70.68%. Singlet oxygen (¹O₂) generation was examined using a chemical method that showed significant enhancement in decomposition rate constant in clung GQDs–PEG–PpIX compared with GQDs and PpIX alone. Afterglow over 600 s showed that GQDs (Se: 0.3%) could be effective for near skin and even deep tumours.     

A thermoluminescence study of Photosystem II back electron transfer reactions in rice leaves – effects of salt stress

The recombination reactions of Photosystem II have been investigated in vivo in rice leaves by using the thermoluminescence (TL) emission technique. Excitation of dark-adapted leaf segments at 0 °C with different number of single turn-over flashes induced the appearance of complex TL glow curves. The mathematical analysis of these curves showed the existence of four TL components: B1-band (temperature maximum, t_max, at 24 °C, originating from S₃Q_B⁻ recombination), B2-band (t_max at 35 °C, from S₂Q_B⁻), AG-band (t_max at 46 °C) and C-band (t_max at 55 °C, from Tyr_D⁺Q_A⁻). Their contributions to the total TL signal were different depending on the number of flashes given. AG-band seems to reflect a special electron transfer from some unknown stroma donor to PS II. Q-band (t_max at 19 °C), originating from S₂Q_A⁻ recombination, was recorded after flashing samples incubated in the presence of DCMU. The recombination halftimes (t_1/2) at 20 °C of S₂Q_A⁻, S₃Q_B⁻, S₂Q_B⁻ and Tyr_D⁺Q_A⁻ were, respectively, 0.8 s, 48 s, 74 s and about 1 h. A sharp AG-band (t_max at 50 °C and t_1/2 of 210 s) could be also observed after illumination of leaves with far-red light and after a dark incubation period of whole plants. Incubation of leaf segments with 0.5 M NaCl abolished the inductions of AG-band by darkness and far-red illumination, significantly decreased Q-band intensity, whereas induced a strong increase in C-band intensity. The possible inhibition of S₂/S₃ formation and quinone oxidation by saline stress are discussed.     

Enhancement of the photoluminescence and long afterglow properties of Sr2MgSi2O7:Eu2+ phosphor by Dy3+ co‐doping

Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ long afterglow phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by powder X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX), and photo‐, thermo‐ and mechanoluminescence spectroscopic techniques. The phase structure of the sintered phosphor was an akermanite type structure, which belongs to tetragonal crystallography. The thermoluminescence properties of these phosphors were investigated and compared. Under ultraviolet light excitation, the emission spectra of both prepared phosphors were composed of a broad emission band peaking at 470 nm. When the Sr₂MgSi₂O₇:Eu²⁺ phosphor was co‐doped with Dy³⁺, the photoluminescence (PL), afterglow and mechanoluminescence (ML) intensity were strongly enhanced. The decay graph indicated that both the sintered phosphors contained fast decay and slow decay processes. The ML intensities of Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphors were increased proportionally with increasing impact velocity, a finding that suggests that these phosphors could be used as sensors to detect the stress of an object. Copyright © 2015 John Wiley & Sons, Ltd.     

Broadband near-infrared (NIR) emitting Cr3+-doped La3Ga5SnO14 phosphor with long persistent and photostimulated persistent luminescence

Recently, long persistent phosphors (LPPs) have attracted significant attention as promising candidates for biomedical applications. However, the serious decrease in luminescence intensity in tissue still remains a major challenge. Therefore, exploring more competitive LPPs and achieving reproducible tissue imaging is crucial. In this study, a new series of near-infrared (NIR) phosphors La₃Ga₅Sn_1-xO₁₄:xCr³⁺ (x = 0.005–0.05) were synthesized using a high-temperature solid-state method. The as-synthesized samples were characterized using X-ray diffraction, diffuse/photoluminescence spectroscopy, fluorescence decay curves, and thermoluminescence spectroscopy. Upon excitation with ultraviolet light, strong emission bands were observed in the range 600–1200 nm with an optimal doping concentration of x = 0.02 mol. Moreover, La₃Ga₅SnO₁₄:Cr³⁺ exhibits persistent luminescence due to the presence of suitable energy traps, which prompted the phosphor to emit NIR light even after the removal of the excitation source.     

The importance of being lucky: A tribute to William Arnold

I present here my tribute to William Arnold, a giant and a pioneer of biophysics of photosynthesis. We honor the man, the science and the philosophy of science he has provided us since 1932.     

UV or blue light excited red persistent perovskite phosphor with millisecond lifetime for use in AC‐LEDs

Energy storage phosphors with millisecond period afterglow that compensate for the diming time of alternating current light‐emitting diodes (AC‐LEDs) have promising application. To obtain a persistent luminescence (PersL) white colour in AC‐LEDs, we focussed on a red afterglow with short period phosphorescence. Ca₄Ti₃O₁₀ forms a type of perovskite‐related Ruddlesden–Popper phase structure. Doping Pr³⁺ ions into Ca₄Ti₃O₁₀, an ideal red PersL was obtained. X‐ray diffraction and element analysis demonstrated that our target samples were crystallized well. Steady‐state and afterglow luminescence properties were investigated in detail. Notably, the PersL intensity was dependent on various excitation wavelengths. By measuring three‐dimensional thermoluminescence spectra, we found that the trap depths showed a continuous distribution and that the shallowest trap contributed to the millisecond afterglow. Two PersL mechanism models were used to elucidate the electron charging and de‐trapping processes under UV or blue light activation.