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Fingerprint patterns (or epidermal ridges) are by far one of the most reliable techniques for individual identification. Fingerprint patterns get deposited on all kinds of solid surfaces due to human transudation or exudation process. Bodily fluids through sweat glands contain moisture, natural oils and proteins. Since latent fingerprint patterns are not readily recognizable they are collected from a crime scene and are further processed physically or chemically. Fingerprints obtained using conventional black and white powders face severe drawbacks including low sensitivity, high background interference from the substrates, involvement of toxic materials, and poor stability. To overcome the above-listed issues, especially for coloured and transparent substrates, luminescent materials have emerged as potential agents for rapid visualization of high-contrast latent fingerprints. This review covers the recent advancements in luminescent nanomaterials of both kinds (up and down conversion) and persistent nanophosphors for developing latent fingerprints. Special emphasis has been given to an unusual class of luminescent materials known as persistent nanophosphors, which do not require a constant excitation, thereby completely eradicating background noise. The review also covers different approaches to gathering fingerprints such as powder dusting, cyanoacrylate fuming, ninhydrin fuming and vacuum metal deposition. [ABSTRACT FROM AUTHOR]

Optical encryption technologies based on persistent luminescence material have currently drawn increasing attention due to the distinctive and long‐lived optical properties, which enable multi‐dimensional and dynamic optical information encryption to improve the security level. However, the controlled synthesis of persistent phosphors remains largely unexplored and it is still a great challenge to regulate the structure for optical properties optimization, which inevitably sets significant limitations on the practical application of persistent luminescent materials. Herein, a controlled synthesis method is proposed based on defect structure regulation and a series of porous persistent phosphors is obtained with different luminous intensities, lifetime, and wavelengths. By simply using diverse templates during the sol–gel process, the oxygen vacancy defects structures are successfully regulated to improve the optical properties. Additionally, the obtained series of porous Al2O3 are utilized for multi‐color and dynamic optical information encryption to increase the security level. Overall, the proposed defect regulation strategy in this work is expected to provide a general and facile method for optimizing the optical properties of persistent luminescent materials, paving new ways for broadening their applications in multi‐dimensional and dynamic information encryption. [ABSTRACT FROM AUTHOR]

Persistent phosphor as a printing anti‐counterfeiting material has attracted strong attention owing to its inherent luminescent decay process and multi‐mode luminescence characteristics under external field stimulation. However, the dynamic persistent luminescence (PersL) pattern of a single material is only manifested in color changes and still faces the problem of being easily decrypted. Herein, a multi‐color luminescent material with a wide range distribution of traps is developed, which can emit strong white PersL. In addition, the phosphors show an intelligent response of thermo‐stimulated luminescence to ambient temperature via recalling the charging temperature of the traps. The PersL mechanism is proposed based on electron transfer between PbO6 and TbO6 octahedrons through the O bridging. Based on the intelligent response of thermo‐stimulated luminescence to temperature, high‐throughput multi‐channel luminescence anti‐counterfeiting can be achieved on a single phosphor recording layer. This study not only provides further insights into the PersL mechanism, but also opens a new door for constructing intelligent responsive anti‐counterfeiting materials. [ABSTRACT FROM AUTHOR]

Long persistent luminescence materials (LPLMs) are promising candidates for various photonic applications, owing to their ability to store light. In spite of advancements in exploring of new LPLMs, the fabrication of transparent centimeter‐sized LPLMs with pre‐designed shapes, high productivity, long afterglow multicolor luminescence, and high chemical stability, is still challenging. Here, high‐throughput manufacture of translucent crystal‐glass composites via a classical injection molding (IM) technique is demonstrated, in which persistent phosphors (PPs)‐amorphous silica nanoparticles‐polymer composites are molded into different shapes then thermally treated at elevated temperatures to obtain glass composites with embedded PP particles and customized shapes. The structural characterizations endorse that the PP particles are preserved during high temperature sintering, and the resultant crystal‐glass composites combine the unique benefits of both PPs and silica glass. Remarkably, the total production time to manufacture 100 pieces of centimeter‐sized crystal‐glass composites is 35 h, thus enabling high‐throughput production of glass composite articles by the IM method. In addition, the injection molded crystal‐glass composites demonstrate long afterglow multicolor luminescence and ultrahigh chemical durability. This study provides a massive production strategy for the fabrication of translucent and stable multicolor persistent luminescent objects with customized shapes, which can be used in numerous applications. [ABSTRACT FROM AUTHOR]

It is well known that near‐infrared (NIR) persistent phosphors have rather low absorption coefficients of biological tissues for NIR light. However, recent research shows that the phosphors emitting NIR lights in second NIR (NIR‐II, 1000–1350 nm) and third (NIR‐III, 1500–1800 nm) biological window have advantages over that in NIR‐I (650–900 nm). Although ZnGa2O4:Ni2+ outputs NIR emission and afterglow locatedin NIR‐II, the weak signal significant limits its application. In this work, persistent luminescent phosphors of ZnGa2O4:xNi2+, yEu3+ (x = 0–0.013, y = 0.01–0.06) (termed as ZEGN) were synthesized via a traditional high‐temperature solid‐state reaction, which feature a broad emission band in the NIR‐II window. The phosphors exhibit a broad NIR emission at about 1300 nm after ultraviolet (UV) or orange–red lights excitation, arising from the 3T2(3F) → 3A2(3F) transition of Ni2+. However, incorporation of Eu3+ ions, the NIR emission intensity significantly increases with the increase of Ni2+ ion concentration, reaching the maximum by 18 times at x = 0.005. Removing the light source, the sample still outputs intense NIR afterglow and red afterglow that can last over 500 s. It is noteworthy that the red afterglow of Eu3+ shows a dramatically decrease but the NIR afterglow increases with increasing the Ni2+ ion concentration, because of energy transfer. Under the excitation of 282‐nm UV light, the ZGEN sample exhibits a good thermal stability. The phosphor offers a promising application in biological imaging due to broadband NIR‐II light and afterglow. [ABSTRACT FROM AUTHOR]

Persistent luminescence is an optical phenomenon where solid phosphors can store photoenergy in defects and release the energy by luminescence after stopping excitation. Due to the intriguing optical characteristics, the defect luminescence based persistent phosphors have attracted enormous attention in recent decades, especially in biomedical fields such as biosensing and bioimaging. Persistent luminescence nanoparticles (PLNPs) can effectively avoid the autofluorescence interference from complex samples or tissues, leading to significantly improved sensitivity in biological analysis. In this review, we summarized the methods to control the optical performance of PLNPs from the perspectives of controlled synthesis and defect regulation, and emphasized the close relationship between their optical performance and applications. We further provided a summary about a series of PLNPs nanoprobes designed by our group for biosensing and bioimaging. Our efforts, summarized in this review, will not only open a window for manipulating luminescence in PLNPs, but also further promote the application of PLNPs in biomedicine. What is the most favorite and original chemistry developed in your research group? Synthesis and bioapplications of persistent phosphors. How do you get into this specific field? Could you please share some experiences with our readers? I got into chemistry related to biomedicine during my graduate student period. The research situation of luminescent nanomaterials in China has a strong effect on me, inspiring me to pursuit new luminescent nanomaterials and their applications. We need have interest and concentrate on our research with passion. We are encouraged to work hard. What is the most important personality for scientific research? Curiosity and hard‐working. What are your hobbies? What's your favorite book(s)? Shopping and reading books. My favorite books are novels, such as "The Three‐Body Problem". How do you keep balance between research and family? I have two boys and it takes me much time to take care of them. I need to elevate my work efficiency and work hard. I also buy household service to save time. Who influences you mostly in your life? My father. He loves reading and writing. I know one need to have passion on something under my father's influence. [ABSTRACT FROM AUTHOR]

Lanthanide ions act as excellent luminescence centers and good charge carrier traps. By selecting proper lanthanide ions, persistent phosphors with the desired luminescent color can be developed. In addition, an appropriate host material can give not only better persistent luminescence performance but also an additional function. Herein, bright white persistent phosphors of Pr3+–Tb3+–Eu3+ tridoped paramagnetic Gd3Ga5O12 (GGG) are successfully developed. The GGG phosphors singly doped with Pr3+, Tb3+, and Eu3+ show reddish‐white (3PJ–3HJ), blue (5DJ–7FJ), and red (5D0–7FJ) photoluminescence, respectively, by UV excitation. On the other hand, the GGG samples codoped with Pr3+–Eu3+ and with Tb3+–Eu3+ show only Pr3+ reddish‐white persistent luminescence and Tb3+ blue persistent luminescence, respectively. Based on the thermoluminescence glow curves, it is found that the Eu3+ ion acts only as an electron trap in the persistent luminescence mechanism and the trapped electrons are released at around 325 K. The cool‐white persistent luminescence is achieved by combining Pr3+ and Tb3+ persistent luminescence centers in the GGG:Pr3+–Tb3+–Eu3+ phosphors. It is demonstrated that the white persistent phosphor powder in water can be dragged around by a permanent magnet due to the paramagnetic property of GGG.

Currently, the efficient detection of fingerprints is essential for the crime investigations. Revealing fingerprints is commonly achieved with fluorescent organic compounds but they are not efficient for fingerprint detection on porous or reflective surfaces. In order to solve the problem of collecting fingerprints on porous/reflective surfaces, inorganic phosphors have been employed, since they have characteristics of variable color emission, afterglow, high chemical stability and nano-size, which allow the fingerprint detection on any porous or non-porous surfaces. Due to these last properties, this review presents a summary about the use of phosphorescent and fluorescent phosphors for the detection of latent fingerprints. First, we discussed the main physical and chemical characteristics of the fingerprints which permit their detection and collection from any surface. After this, we presented the main morphological, structural and luminescent properties of the phosphorescent and fluorescent phosphors that allow their use for fingerprint detection. Later, we demonstrated with pictures of fingerprints (with and without light emission from the phosphors deposited on them) that both, phosphorescent and fluorescent phosphors can be used to visualize fingerprints with high resolution and high contrast without interference of the background surface, which is ideal for its collection and registration in the Automated Fingerprint Identification System (AFIS). We believe that this review could be useful to understand how to select an appropriate phosphorescent or fluorescent material for fingerprint detection depending on the type of surface (porous or non-porous, reflective or not reflective) where the fingerprint is deposited. [ABSTRACT FROM AUTHOR]

Near-infrared persistent luminescence materials have recently attracted considerable attention in the field of bio-imaging, food analysis, anti-counterfeiting, etc. However, the limited number of efficient emitters restricts their further development. Herein, a novel broadband near-infrared long persistent phosphor Na 2 CaGe 5 SiO 14 :xCr3+ was synthesized using a high-temperature solid-phase method. Its emission range is mainly within 600–900 nm, and the persistent luminescence duration of the phosphor with the optimal doping concentration is more than 12 h. The optical properties of the samples and the relationship between the crystal field and chromium ion concentration were systematically investigated by UV diffuse reflectance spectra as well as fluorescence spectra, and the occupancy of Cr3+ ions in the Na 2 CaGe 5 SiO 14 matrix was probed. The energy transfer process between Cr3+ ions at different temperatures and the decay behavior at different emission wavelengths were further analyzed in conjunction with low-temperature spectra and photoluminescence decay curves. Finally, Cr ion-doped silicogermanate near-infrared long persistent luminescent materials were tested for biological tissue penetration, demonstrating their potential applications in bio-imaging. [Display omitted]. • A new broadband emitting persistent phosphor with excellent performance is presented. • The Cr3+ dopant ions occupy different lattice positions, leading to different emission properties. • The Cr-ions act as a probe for local symmetry in the lattice. • The phosphor has high application potential in bio-imaging applications thanks to its high tissue penetration. [ABSTRACT FROM AUTHOR]

Although carborane‐based luminescent materials have been studied for years, no persistent phosphor has been reported so far. Herein, we describe boron‐cluster‐based persistent phosphors obtained by linking a σ‐aromatic carboranyl cage to the π system of a carbazolyl group. The carboranes were found to promote intersystem crossing from a singlet to a triplet state. The rigid boron cluster was able to stabilize the ultralong triplet excitons through multiple nonclassical hydrogen bonds, such as B−H⋅⋅⋅π interactions, thus leading to a long lifetime of up to 0.666 s and an absolute phosphorescence quantum yield of 7.1 %, which is outstanding for an organic phosphor without heavy atoms. These phosphors can be excited by visible light and show dynamic emission behavior, including thermochromism and mechanochromism. This study demonstrates that non‐metal/heavy‐atom boron clusters can be used to develop multifunctional high‐performance phosphors for potential applications. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) long‐persistent phosphors (LPPs) have emerged as a potential solution for bio‐imaging applications over the past few years. However, there are enormous challenges regarding their in situ application based on their dependence on short‐wavelength excitation. In this paper, we report a multi‐spectral excited NIR LPP, Li5Zn8Ga5Ge9O36: 1.5 % Cr3+, 0.5 % Ti4+, which overcomes the limitations of functional processes in biological tissues and other complex systems. This LPP exhibits a high luminescent intensity and a long emission duration in the NIR region (700–800 nm). The applicability of this phosphor to tissue imaging is demonstrated experimentally. Its persistent luminescence (PersL) can easily penetrate approximately 2 mm of pork flesh. More importantly, this phosphor can be re‐charged in situ using a red LED or laser diode array to provide renewed NIR PersL for biological tissues, which is beneficial for long‐term biological tissue imaging applications with high signal‐to‐noise ratios. Systematic investigations of the nature of energy traps and PersL mechanisms are also reported in this paper. [ABSTRACT FROM AUTHOR]

Abstract The dysprosium and boron effect on the emission properties of europium-doped SrAl 2 O 4 samples has recently attracted considerable attention due to their high brightness and long afterglow. Here, the influence of both cations, Dy3+ and B3+, on the spectroscopic properties of the europium free samples SrAl 2 O 4 :Dy3+ and SrAl 2 O 4 :Dy3+, B3+ has been investigated in order to get more insights concerning the mechanism by which they enhance the afterglow. Unique features have been observed in their excitation and emission spectra that show on one hand the lattice defects induced by the replacement of Sr2+ by Dy3+ and proves the existence of different crystallography sites for the Dy3+ ions and on the other hand, the local distortion of the energy levels of Dy3+ ions in the presence of B3+. Highlights • Sr2+ replacement by Dy3+ in SrAl 2 O 4 with two different Dy2+ sites. • Strong influence of boron addition in SrAl 2 O 4 :Dy3+ in absorption, excitation and luminescence spectra. • Local distortion of the Dy3+ environment upon incorporation of boron with higher affinity of boron for one of the Dy3+ sites around which the distortion is stronger. [ABSTRACT FROM AUTHOR]

Abstract This review paper provides a description of direct recombination processes between carriers from traps to luminescent centers, involving the occurrence of a tunneling mechanism between their space-correlated localized electronic levels. The experimental evidences that allow to recognize tunneling recombination in phosphorescence time decay and thermoluminescence experiments are first outlined, and compared with those characteristic of recombination processes involving the transfer of carriers in the delocalized bands prior to their recombination. Simple explanations are also proposed for the phenomenological observations in both athermal and thermally assisted tunneling processes. The importance of such recombinations in three material classes – scintillators, persistent phosphors, and dosimeters, is then outlined and discussed in relation to the material requirements in their distinct application fields. For each application, numerous literature examples are reported. Finally, the paper is complemented by a brief illustration of literature investigations describing experimental evidences of direct trap-center recombination different from tunneling, mostly based on the inspection of emission spectra and thermoluminescence glow curve shapes. Highlights • Decription of localized, tunneling recombinations from an experimental and materials science oriented point of view. • Characteristics of athermal recombinations. • Athermal tunneling versus distribution of trap levels. • The role of temperature: thermally assisted tunneling. • Influence of tunneling processes in several material classes - scintillators, phosphors, dosimeters. [ABSTRACT FROM AUTHOR]

In this work we report on the thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of β-Na(Gd,Lu)F4:Tb3+ nanophosphors prepared via a standard high-temperature coprecipitation route. Irradiating this phosphor with X-rays not only produces radioluminescence but also leads to a bright green afterglow that is detectable up to hours after excitation has stopped. The storage capacity of the phosphor was found to be (2.83 ± 0.05) × 1016 photons/gram, which is extraordinarily high for nano-sized particles and comparable to the benchmark bulk phosphor SrAl2O4:Eu2+,Dy3+. By combining TL with OSL, we show that the relatively shallow traps, which dominate the TL glow curves and are responsible for the bright afterglow, can also be emptied optically using 808 or 980 nm infrared light while the deeper traps can only be emptied thermally. This OSL at therapeutically relevant radiation doses is of high interest to the medical dosimetry community, and is demonstrated here in uniform, solution-processable nanocrystals.

Leading to advancement in technological manifestations the phenomenon of persistent luminescence and growth of luminescent materials has witnessed a rapid headway in research and development. It is an optical phenomenon, also referred as long lasting phosphorescence and is applied effectively in safety indications, emergency lighting, graphic arts, interior decoration, multidimensional optical memory and detection of high energy UV, X-rays and β rays. Persistent luminescence is the underlying mechanism that constitutes one of the aspects of solid state lighting technology. LED light bulbs are extremely energy efficient and sustainable since the power consumption is brought down by 80% when compared to conventional light bulbs. Such low energy consumption can save millions in energy costs and can provide eco-friendly sustainable lighting worldwide. Since sustainable energy services are central to economic development, pioneered use of LED lighting powered by renewable energy will cause positive impact not only on environment through reduced carbon dioxide emission and less deforestation but will also provide a cheaper source of lighting to people. The paper highlights the principle working of persistent phenomenon through various models. It also explores the advancement made in this arena through various research input. We are working with the probability of generation of reliable, compact and efficient LEDs with a couple of phosphor systems. Nevertheless, sustainability is multi-faceted. Though LED lighting is worth significant from energy consumption standpoint it is struggling with respect to finite material usage and recyclability. Constant efforts are raised to overcome these shortcomings. [ABSTRACT FROM AUTHOR]

Lighting-related energy consumption has recently increased due to the significant expansion of buildings' floor area and the growing demand for lighting coming from the occupants. With the aim of mitigating the global warming phenomenon by reducing the impacts of fossil fuels-powered systems, the lighting sector has faced a continuous renovation through years, up to the modern and efficient light emitting diodes (LEDs) solutions. Moving from the basic principle of phosphor-converted LEDs, consisting in the combination of phosphor materials to the radiation emitted by a LED chip, the present research investigates the response of photoluminescent pigments with different absorption and emission spectra as a function of the specific spectral distribution of the excitation source. The evolution of photoluminescence is later investigated during both the charging and the decay phase. The performance of each "pigment–lamp" pair is characterized using a spectroradiometer and a specially designed experimental equipment. Results demonstrate how a yellow-emitting material is more suitable than others for lighting purposes, providing for the highest luminance values (up to 2.61 cd/m2) and the longest decay time (> 5 h). Moreover, the fastest activation of luminescence due to UV radiation (after 20–60 min of exposure) does not guarantee the most persistent and intense performance of the samples. [Display omitted] • The coupling of photoluminescence and artificial light is studied for energy saving. • Rare-earth pigments with various luminescent colors are exposed to multiple irradiating spectra. • Photoluminescence evolution is monitored during both the charge and discharge phase. • Different irradiations significantly change the re-emission of the same pigments. • A yellow afterglow charged by blue or white light is the most suitable for lighting. [ABSTRACT FROM AUTHOR]

Recently, near-infrared (NIR) persistent phosphors become a research hotspot in biomedical application, because of their rather low absorption coefficients of biological tissues for NIR light. Most investigated phosphors emit NIR lights, whose wavelengths are no more than 1000 nm and located in NIR-I biological window. However, the phosphors emitting NIR lights in second (NIR-II, 1000–1350 nm) and third (NIR-III, 1500–1800 nm) biological window have advantages over that in NIR-I one. Here, persistent luminescent phosphors of ZnGa 2 O 4 : x Ni2+ (x = 0–0.01) were synthesized via a traditional high-temperature solid-state reaction, which feature a broad emission band in the second near-infrared (NIR-II) window. Ni2+ tends to occupy Ga3+ site in ZnGa 2 O 4 , which results in the formation of oxygen vacancy. Upon ultraviolet (UV) or orange-red lights excitation, the phosphors exhibit a broad NIR emission at about 1300 nm, arising from the 3T 2 (3F)→3A 2 (3F) transition of Ni2+. Removing the light source yields intense NIR afterglow, with the duration longer than 500 s. Strongest NIR emission and best persistent luminescence are found for the x = 0.005 sample, which is excited by 254-nm UV light. The ZnGa 2 O 4 :Ni2+ persistent phosphors have potential application in vivo imaging, because of their charming emissions and afterglows with the wavelength locating in NIR-II window. [Display omitted] • Persistent luminescent phosphors of ZnGa 2 O 4 : Ni2+ were synthesized. • Ni2+ tends to occupying Ga3+ site in ZnGa 2 O 4 , resulting in the formation of oxygen vacancies. • The phosphors have charming emissions and afterglows locating in NIR-II window. • The phosphors have potential application in vivo imaging. [ABSTRACT FROM AUTHOR]

Highlights: [•] Persistent phosphor SrAl2O4:Eu2+ was synthesized and studied. [•] Ab initio calculations of its electronic properties were performed. [•] Lowest position of the Eu 4f states in the band gap was determined. [•] Position of the Eu 4f states agrees with the charge transfer transition. [Copyright &y& Elsevier]

Abstract: Ceramic specimens of singly doped Lu2O3:Tb, and doubly activated Lu2O3:Tb,Ca, Lu2O3:Tb,Hf and Lu2O3:Pr,Hf were prepared and their thermoluminescent properties were investigated. After irradiation with X-rays or deep-UV photons the singly doped Lu2O3:Tb was found to produce a glow curve with a few thermoluminescent bands spread across the temperature range of 50–450°C. (Tb,Ca) co-doped material produced basically one strong thermoluminescent band peaking at around 120°C and thus was able to produce persistent luminescence lasting about 10h, as visible to the human eye. In the (Tb,Hf) co-doped ceramics the thermoluminescence at around 100°C was seen as a vestige only and was responsible for persistent emission lasting merely a few minutes. Instead, a strong thermoluminescence glow band at around 250°C appeared. Its intensity faded by about 10% after 6hours in the dark. Lu2O3:Pr,Hf co-doped ceramics also showed intense thermoluminescence with the main components at around 200°C and 270°C. The latter was found not to fade in time, while intensity of the former dropped by about 7–8% after 6h. All these effects were observed in ceramics processed at temperatures as high as 1700°C. It is proposed that high temperature of processing is necessary as only then clustering of individual defects occurs and the energy released upon heating can diffuse towards the nearby located emitting center efficiently. [Copyright &y& Elsevier]

Abstract: Mg x Sr1− x Al2O4:Eu, Dy (x =0.05–0.25) phosphors were prepared by the solid-state reaction method; their excitation and emission spectra corresponding to the transitions between the ground 4f7 and excited 4f65d1 configurations of Eu2+ ion were studied. Broad band UV excited luminescence attributed to Eu2+ ions was observed around 19,500cm−1 (513nm). From the comparison between the excitation and emission spectra, the crystal field splitting of the Eu2+ 5d states and the parameters of electron–vibrational interaction, such as the Huang–Rhys factor, effective phonon energy, and zero-phonon line position for the studied compound were estimated for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Cr3+ activated red long persistent phosphorescence through persistence energy transfer from Eu2+ to Cr3+ has been reported in strontium aluminates co-doped with Cr3+, Eu2+ and Dy3+. The decay processes of the red long persistent phosphorescence at 693nm emission exhibit strong behavior of f–d band of Eu2+, indicating the occurrence of energy transfer from Eu2+ to Cr3+. Lifetime measurements of the blue band show that the energy transfer rates increase with the increase of the Cr3+ concentration. There are several phases observed in the strontium aluminates. Energy transfer occurs only for the Eu2+ and Cr3+ ions that located in the same phase in the host. In SrAl12O19 phase, the Eu2+ ions emit blue light centered at 400nm and prefer to transferring energy to the Cr3+ that yields 688nm emission, while in the Sr2Al6O11 and Sr4Al14O25 phases, the Eu2+ ions emit at 460 and 490nm, respectively, and transfer the energy to the Cr3+ ions that give emission at 693nm. It is found that the persistent phosphorescence only consists of the 490 and 693nm bands, indicating the dominant contribution to the phosphorescence is from the ions in the Sr4Al14O25 phase. [Copyright &y& Elsevier]

Mn2+ activated long persistent phosphors, CaAl2O4:Mn2+, Ce3+, Ca2Al2SiO7:Mn2+, Ce3+ and MgSiO3:Mn2+, Eu2+, Dy3+, were prepared. Long persistent phosphorescence in green, yellow, and red have been observed in the systems with persistence time over 10 h for the green (525 nm) and the yellow (550 nm) and 4 h for the red (660 nm). Emission and excitation spectra showed that Mn2+ emission was dominant in these materials. Long persistent phosphorescence was also measured in the systems without Mn2+ as a co-dopant. The emissions were much stronger due to 5d–4f transitions in Ce3+ and Eu2+ other than 3d–3d transitions in Mn2+. The disappearances of the long persistent afterglow in these systems when co-doped with Mn2+ suggested the existence of a strong persistent energy transfer from Ce3+ and Eu2+ to Mn2+. [Copyright &y& Elsevier]

A series of infrared long persistent phosphor samples of ZnAl 2 O 4: Cr3+ with various doping concentrations of Ge4+ ions were synthesized via a high temperature solid state reaction method. Powder X-ray diffraction, persistent spectra, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Ge4+ ions on the luminescence in the spinel structure. The results define an optimal co-doping of germanium ions (2 mol%) in the ZnAl 2 O 4 : Cr3+ can enhance the afterglow time of the phosphor. With the increase of co-doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Thermoluminescence data emphasise there are modifications from the presence of the Ge ions. The phenomenon that the long-wave emission reaches the maximum value of the spectral spread before the short-wave signal provides interesting insights into the charge transfer process. • The material can maintain an unusually long signal persistence after being excited by visible light. • 2 mol% is the optimized concentration in terms of afterglow. • The asymmetry of TL spectra indicate clear evidence for there being a tunnelling process involved. [ABSTRACT FROM AUTHOR]

A series of Zn 1·8 Al 1.6 Ge 0.2 O 4: Cr3+ x mol% (x = 0.5, 1, 1.5, 2, 2.5, 3) phosphors were synthesized via a high temperature solid state reaction. It was shown in the previous study that suitable germanium substitution in the original ZnAl 2 O 4 : Cr3+ infrared long persistent phosphors can enhance the afterglow time. In this paper, powder X-ray diffraction, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Cr ions on the luminescence in the spinel structure. With the increase of doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Meanwhile, according to the photoluminescence, the excitation emissions of Cr3+ shift which respond to the structural changes. The Stoke and anti-Stoke lines of Cr3+ infrared emission are noticeable for these samples and the dependence of these lines with temperature is demonstrated. Both thermoluminescence (TL) and afterglow results prove that 1.5 mol% Cr is the optimized doping concentration. All the results indicate that with a suitable concentration, Zn 1·8 Al 1.6 Ge 0.2 O 4: Cr3+ could be prepared as an excellent infrared long afterglow phosphor and the emission lines of Cr ions are excellent probe ions that record structural changes. • The excitation emission spectra of Cr3+ alter with the doping concentration. • 1.5 mol% is the optimized doping concentration in terms of after glow. • The diffraction peaks shift to smaller angles with increases in doping. • Overall the performance has been increased. [ABSTRACT FROM AUTHOR]

Abstract: Novel red long persistent phosphors of BaMg2Si2O7:Mn2+, Eu2+, Dy3+ have been synthesized at high temperature and weak reductive atmosphere. There are a deep blue emission with peak wavelength of 400nm and a broader emission band centered at 680nm when excited by 340nm. The broad emission band is attributed to the spin-forbidden transitions of the d-orbital electrons associated with the Mn2+ ions (4T1(4G)–6A1(6S)). The excitation and emission spectra of the samples with different dopants and doping concentrations show that the Mn2+ emission is dominantly due to the persistent energy transfer from Eu2+. Red long persistent phosphors have been observed in the system for over 2h. [Copyright &y& Elsevier]

Effective green long persistent phosphors (LPP) Sr 4 Al 14 O 25 :Eu2+ and Sr 4 Al 14 O 25 :Eu2+, RE3+ (RE = Nd, Dy) were prepared using solution combustion procedure at 600 °C and reheated for two hours at 1150 and six hours at 1350 °C in tube furnace in the reducing environment (in presence of 95 % N 2 and 5 % H 2). The effect of codopants (Nd3+ and Dy3+) on the luminescent and structural characteristics of materials were studied using photoluminescence (PL) spectroscopy, powder X-ray diffraction (PXRD), Fourier transformation infrared (FTIR) and transmission electron microscopy (TEM). The influence of concentration of dopant ions on the PL intensity was examined by varying Eu2+ concentration (0.01-0.05 mol) in host matrix. The incorporation of 0.03 mol Eu2+ ion in Sr 4 Al 14 O 25 lattice produces maximum PL intensity. On 363 nm excitation, strong broad emission band is observed at 480−520 nm corresponding to 4f65d1→4f7 transition of divalent europium ions. The persistency and luminescence intensity is found to improve by doping Nd3+ and Dy3+ ions as codopants and also with increasing the temperature. PXRD study confirms the formation of single phase orthorhombic crystal symmetry with Pmma space group. The crystallinity of the materials increases with temperature. FTIR spectra determine the stretching and bending modes of vibrations to confirm the formation of metal-oxygen bonds. TEM images demonstrate the synthesis of nearly spherical shaped nanoparticles. [ABSTRACT FROM AUTHOR]

In this work we report on the thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of β-Na(Gd,Lu)F4:Tb3+ nanophosphors prepared via a standard high-temperature coprecipitation route. Irradiating this phosphor with X-rays not only produces radioluminescence but also leads to a bright green afterglow that is detectable up to hours after excitation has stopped. The storage capacity of the phosphor was found to be (2.83 ± 0.05) × 1016 photons/gram, which is extraordinarily high for nano-sized particles and comparable to the benchmark bulk phosphor SrAl2O4:Eu2+,Dy3+. By combining TL with OSL, we show that the relatively shallow traps, which dominate the TL glow curves and are responsible for the bright afterglow, can also be emptied optically using 808 or 980 nm infrared light while the deeper traps can only be emptied thermally. This OSL at therapeutically relevant radiation doses is of high interest to the medical dosimetry community, and is demonstrated here in uniform, solution-processable nanocrystals. [ABSTRACT FROM AUTHOR]