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Red-emitting Mg4 Nb2 O9 :Eu(3+) phosphor is synthesized via a solid-state reaction method in air, and its crystal structure and luminescence are investigated. The phosphor can be excited efficiently by ~ 395 nm light, coupled well with a ~ 395 nm near-ultraviolet chip and emits red light at ~ 613 nm with sharp spectra due to (5) D0  → (7)  F2 transition of the Eu(3+) ion. Mg4 Nb2 O9 :Eu(3+) phosphor sintered at 1350 ºC shows Commission international de I'Eclairage (CIE) chromaticity coordinates of x = 0.6354, y = 0.3592, and is a potential red-emitting phosphor candidate for white light-emitting diodes (W-LEDs) under ~ 395 nm near-ultraviolet LED chip excitation., (Copyright © 2014 John Wiley & Sons, Ltd.)

A variety of materials sintered in different atmosphere have been well investigated, but there are few reports on the long-persistent phosphorescent materials, especially the near-infrared long-persistent phosphorescent materials sintered in various atmosphere. Changing the surrounding atmosphere is an effective method to improve the afterglow properties of the materials. In this work, we fabricate a typical kind of near-infrared long-persistent phosphorescent materials of Zn3Ga2Ge2O10: 0.5% Cr(3+) in neutral, oxidizing, and reducing atmosphere. By analyzing the XRD patterns, afterglow spectra, decay and thermo-luminescence curves, we discuss the great effects on the structure, long persistent properties and trap properties of the phosphor. This work of obtaining the Zn3Ga2Ge2O10: 0.5% Cr(3+) is of great potential in the applications in night-vision surveillance and in vivo bio-imaging., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Graphite like C3N4 (g-C3N4) was synthesized facilely via the low temperature thermal condensation of melamine between 300-650°C. The results showed that the products maintained as melamine when the temperature is below 300°C. With the increase of temperature, the products were transformed into carbon nitride and amorphous g-C3N4 successively. The morphology of products was changed from spherical nanoparticles of melamine into layer carbon nitride and g-C3N4 with the increase of temperature. The photoluminescence spectra showed that the carbon nitride products have continuous tunable photoluminescence properties in the visible region with increasing temperature. With the help of steady state, transient state time-resolved photoluminescence spectra and Raman microstructural characterization, a novel tunable photoluminescence mechanism was founded systematically, which is mainly related to the two dimensional π-conjugated polymeric network and the lone pair of the carbon nitride.

Superbroad near-to-mid infrared (NIR-MIR) photoluminescence was observed from Bi5(AlCl4)3 at room temperature, spanning the spectral range of about 1000 to 4000 nm. On the basis of structural considerations and dynamic analyses, Bi5(3+) clusters were identified as the optically active species, inherently differing from the species which is typically believed to be active in NIR-emitting Bi-doped glasses. In comparison to most other NIR-luminescent Bi-doped materials, the MIR-part of the luminescence spectrum is still present at room temperature. Emission intensity and excited state lifetime were found to exhibit abnormal temperature dependence, where the former increases with temperature up to a critical value of about 150 K. This behavior is related to a temperature-dependent overlap between ground state and excited states. The observed stabilization of MIR photoemission at room temperature may be a starting point for the development of Bi-based NIR-MIR light sources with superbroad emission spectrum, where Bi5(3+) or similar polycationic species act as optical gain medium.

Aluminum-lanthanum-silicate glasses with different Eu doping concentration have been synthesized by conventional melt-quenching method at 1680 degrees C in reductive atmosphere. Under 395nm excitation, samples with low Eu doping concentration show mainly the cyan broad emission at 460nm due to 4f(6)5d(1)-4f(7) transition of Eu(2+); and the samples with higher Eu doping concentration show mainly some narrow emissions with maximum at 616nm due to (5)D(0)-(7)F(j) (J=0, 1, 2, 3, 4) transitions of Eu(3+). Cyan-white-red tunable luminescence under 395nm excitation has been obtained by changing the Eu doping concentration.

Lanthanide doped nanoparticles (NPs) exhibit tunable X‐ray‐excited optical luminescence and X‐ray‐excited persistent luminescence (XEPL), holding broad prospects for applications in display/anti‐counterfeiting and X‐ray imaging. The development of effective strategies for multi‐dimensional applications based on lanthanide‐doped fluoride NPs are a constant challenge. Here, core–shell structured fluoride NPs, in which the heavy metal fluoride shell effectively suppresses the non‐radiative relaxation and simultaneously improve the X‐ray absorption of the shell are designed and fabricated. Under X‐ray irradiation, the developed NPs exhibit an increased number of secondary electrons which migrate to Er3+ centers at the interface and greatly improve the XEPL intensity. Additionally, the introduction of Mn2+ further enhances the XEPL intensity and offers an effective route to control the red‐green ratio of the upconversion spectrum. The NPs co‐doped with Mn2+ exhibit a bright green XEPL under X‐ray irradiation and a red emission under 1532 nm laser excitation. It is further validated that these NPs can be utilized for advanced anti‐counterfeiting and high‐resolution delayed imaging based on a film containing NPs as a scintillation screen. These findings suggest a new strategy of designing Er3+ doped NPs for multi‐dimensional applications. [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]

Near‐infrared (NIR) photonic materials find extensive applications across important fields such as telecommunications, laser radar, and atmospheric remote sensing. In particular, photonic materials activated by main group elements, which exhibit unique spectral features including ultra‐broadband tunable luminescence and long lifetime, have become rising stars in NIR emitting dopants. In this review, the energy level characteristics of the p‐electrons to gain insight into the fundamentals of the NIR optical response from the main group elements are first introduced. Next, the NIR luminescence properties of the main group elements are discussed. Then, the strategy for the design of main group elements activated materials with the desired properties based on local chemical environment engineering is proposed. In addition, recent advances in the applications of main group element (excluding bismuth) activated materials are highlighted. Furthermore, the key scientific issues that urgently need to be solved for such materials, such as the detailed luminescence mechanism are highlighted. Anticipation also extends to the future research trends in this exciting field, including the ways for enhancing luminescence efficiency and extending spectral region, and the efforts for implementing these advancements in novel cutting‐edge technologies like photovoltaics and biomedicine. [ABSTRACT FROM AUTHOR]

Effective online monitoring of the spatial distribution of high‐energy radiation is of significant importance in various fields such as medical imaging, high‐energy physics, and homeland security. However, achieving radiation detectors with both high sensitivity and minimal disturbance is an enormous challenge. The present study introduces a solution to this bottleneck issue through the development of a full‐inorganic scintillating fiber, successfully demonstrating its application in constructing a radiation monitoring device. The scintillating fiber, activated with Ce3+ and fabricated using the melt‐in‐tube approach, is lightweight with a density of 2.5 g cm−3 and exhibits efficient scintillating emission with a light yield of 4000 photons MeV−1. These characteristics enable the achievement of radiation detection with high sensitivity while keeping disturbance to the incident radiation beam at a minimum. Furthermore, 2D and 3D radiation beam monitors are constructed based on these scintillating fibers, facilitating spatial radiation monitoring. The findings demonstrate that full‐inorganic scintillating fibers and devices offer a synergistic combination of high sensitivity and negligible disturbances. This progress not only introduces a novel full‐inorganic fiber for radiation detection but also suggests promising applications in various nuclear fields where 3D radiation beam tracking is essential. [ABSTRACT FROM AUTHOR]

With the rapid development of 5G networks, the Internet of Things, and new‐generation of AI, there are considerable demands on expanding the capacity of contemporary optical fiber communication systems. One of the most effective avenues involves the extension of the bandwidth of Er‐doped fiber amplifiers, but with limited success. Herein, an Er‐activated hybridized glass fiber are reported, which can help realize broadband telecommunication. The effect of element hybridization on the bandwidth of Er‐activated fiber is clarified and the structure‐optical response relationship is established. A two‐step deposition approach is proposed to overcome the immiscibility barrier of different hybridized elements, and Er‐activated fiber with uniform doping is constructed. The activated fiber presents excellent compatibility with commercial telecommunication systems, providing a small signal gain of >13 dB in the whole L‐band range and a maximum gain of 28 dB. Furthermore, the Er‐activated fiber amplifier device is successfully developed. It exhibits outstanding optical amplification performance with gain >24 dB in the range of 1580–1624 nm, gain fluctuation less than ±0.9 dB, and noise figure <6.5 dB. The results not only provide a new strategy for developing novel active broadband optical fibers, but a valuable solution for new‐generation large‐capacity optical fiber communication systems. [ABSTRACT FROM AUTHOR]

Excitation polarized upconversion luminescence (EPUL) from lanthanide ions has attracted considerable attention due to its wide applications in microfluidics, single particle tracking, security inks, and cell internal viscosity testing. However, controlling the degree of excitation polarization (DOEP) of the EPUL remains a significant challenge. Here, the modulation of the DOEP (from 0 to 0.5) of the EPUL from Er3+ doped single nanorods by changing the concentration of doped Er3+, Yb3+, or Mn2+ is systematically studied. By analyzing the lifetimes and disproportionate changes in luminescence intensities, it is found that optimizing Er3+, Yb3+, or Mn2+ concentration can reduce non‐radiative transition and population density in excited states, leading to the enhancement of the DOEP under a good alignment of transition dipoles. Furthermore, the possibility of anti‐counterfeiting based on such tunable EPUL is illustrated. Three kinds of fine patterns with a small size of 10 µm are realized by assembling the single nanorods accurately via optical tweezers. The patterns and their EPUL guarantee double protection for the feasibility of anti‐counterfeiting. The findings of this study offer insights into the EPUL from lanthanide ions and provide a microscale platform via the EPUL for the application of multidimensional information encoding and reconfigurable double anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

The fabrication of multicolor luminescent glass with simultaneous controlling of the distribution of emission colors within a monolithic medium has been a tremendous challenge, which, however, could be attractive for diverse photonic applications from optical storage to information encryption. Here, a space‐selective doping method based on a stereolithographic technique is designed, enabling the control of the doping domain of the active luminescence ions, such as Eu3+, Ce3+, Tb3+, and Pr3+, in 3D‐printed single silica glasses. The printed glass shows intense multicolor luminescence, and the interface between the two doping areas is invisible under natural light. By using this technique, multicolor luminescent glass with pre‐designed emission color distribution is fabricated, which enables facile and nondestructive decryption strategies based on photoluminescence under controlled excitation conditions. Besides, the extending of this strategy by using a femtosecond laser for photopolymerization dramatically improves the printing resolution down to the few‐micron scale, enabling the multi‐dimensional optical storage and encryption in miniaturized glass items. This work not only delineates the potential applications of multicolor luminescent glass for multi‐dimensional anti‐counterfeiting and information storage, but also opens up new avenues for prospective applications in sensing, lasers, and displays based on glasses with spatially engineered optical responses. [ABSTRACT FROM AUTHOR]

Bismuth(Bi)‐doped photonic materials with broadband near‐infrared luminescence can be used in applications such as high‐capacity fiber communication, fiber laser, and biological imaging. The scalable fabrication of Bi‐doped fibers with high dopant solubility, high optical activity, and broadband optical response still remains a significant challenge. In this study, the comprehensive studies on the physical, chemical, mechanical, and optical responses of a Bi‐doped glass system are performed and a Bi‐doped germanate multicomponent glass system is proposed to be the promising candidate. The deactivation mechanism of Bi in a glass matrix is investigated and prevented by controlling the fiber drawing. In addition, a Bi‐doped multicomponent germanate glass fiber with a high level of Bi doping is successfully constructed. Finally, a principle compact fiber amplifier device is fabricated for broadband optical amplification. This device can be potentially used for increasing the capacity of telecommunication systems. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphors have recently received considerable attention in spectroscopy technology fields, but designing inexpensive, emission peaks centered above 800 nm, and multimodal broadband NIR luminescence material still remains a great challenge. Here, by selecting stannate compound Mg2SnO4 (MSO) as the host, a kind of broadband NIR phosphor MSO:Cr3+ with multimode luminescence properties is reported. The designed material exhibits an emission peaking at 800 nm and a full‐width at half maximum of 180 nm (≈2730 cm−1). The site occupation of Cr3+ in MSO is unraveled by density functional theory calculation. The constructed NIR light‐emitting device based on MSO:Cr3+ displays a high NIR output power of 187.19 mW@100 mA and remarkable photoelectric efficiency of 13.67%, and its multifunctional applications in information encryption, non‐destructive detection, and so on are also demonstrated. Additionally, through defect site reconstruction, MSO:Cr3+ presents superior broadband NIR persistent luminescence (PersL) properties with PersL duration time longer than 50 h. This work provides a feasible strategy to develop intelligent optical material integrated with multimodal luminescence through low‐cost stannate compounds as the host toward versatile applications such as non‐destructive detection and bioimaging. [ABSTRACT FROM AUTHOR]

Orthogonal upconversion nanoparticles (UCNPs) have received increasing research attention due to their unique optical performance. However, the establishment of the orthogonal UCNPs emitting primary red/green/blue (RGB) UCL remains a great challenge. Herein, RGB‐switchable NaErF4‐cored core–multishell UCNPs (RGB‐UCNPs) are constructed through the coordinative implementation of outside‐in cascaded photon harvesting and interfacial energy‐transfer (IET) inhibition. By modulating several constructional factors, the power‐density‐independent red, green, and blue luminescence in high color purity is readily available in the elaborated RGB‐UCNPs under 1550, 808, and 980 nm excitations, respectively. Notably, full‐color emissions, involving red, yellow, green, cyan, blue, magenta and white, are dynamically implemented in this single architecture through manipulating the excitation power of the combined 1550/808/980 nm lasers. These emission profiles of RGB‐UCNPs make them promising in broad photonic applications. As a proof of concept, the viability of the logicalized information encryption strategy and smartphone APP‐assisted multimodal luminescent QR code anti‐counterfeiting technique is demonstrated, which are both established based on directly useable RGB‐UCNPs with assistance of a self‐built combined laser system. This work not only opens up a new avenue to gain RGB‐switchable UCL and flexible full‐color output in a single nanostructure, but also provides enlightenment for developing the application scenarios of multicolor‐tunable UCNPs. [ABSTRACT FROM AUTHOR]

With the implementation of the Minamata Convention on Mercury, there is an urgent need to find a new way to generate ultraviolet‐C (UVC) light to replace mercury lamp. Upconversion phosphors have the potential to generate UVC light as they are able to convert low energy photons into high energy emissions. Here a new Sr2SiO4:Pr3+ phosphor is reported that could emit UVC light under excitation of a commonly used 450 nm laser diode, a cheap blue light‐emitting diode (LED) with central emitting wavelength at 450 nm, and even sunlight. Moreover, the potential applications of the UVC light of Sr2SiO4:Pr3+ phosphor upon excitation at 450 nm are demonstrated in several different situations, including static marking and dynamic tracking. Demonstration of the unique advantage of photon‐upconverted UVC emission of Sr2SiO4:Pr3+ in the application of sterilization is mainly focused, especially when the deep ultraviolet (DUV) LED cannot work adequately. This work opens a new route for generating UVC light and expands the applications of photon‐upconverted UVC emission, which is expected to be an indispensable supplement to the deep ultraviolet LED. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) are newly emergent broadband light sources for miniaturizing optical systems like spectrometers. However, traditional converters with NIR phosphors encapsulated by organic resins suffer from low external quantum efficiency (EQE), strong thermal quenching as well as low thermal conductivity, thus limiting the device efficiency and output power. Through pressureless crystallization from the designed aluminosilicate glasses, here broadband Near‐infrared (NIR) emitting translucent ceramics are developed with high EQE (59.5%) and excellent thermal stability (<10% intensity loss and negligible variation of emission profile at 150 °C) to serve as all‐inorganic visible‐to‐NIR converters. A high‐performance NIR phosphor‐converted light emitting diodes is further demonstrated with a record NIR photoelectric efficiency (output power) of 21.2% (62.6 mW) at 100 mA and a luminescence saturation threshold up to 184 W cm−2. The results can substantially expand the applications of pc‐LEDs, and may open up new opportunity to design efficient broadband emitting materials. [ABSTRACT FROM AUTHOR]

Spinel configuration is a kind of broadly considered host candidate when designing persistent luminescence (PersL) materials due to the easy generation of vacancies and anti‐site defects. Here, a new strategy of defect enrichment for the activation of PersL is proposed, and in contrast to the spinel configuration, it is demonstrated that the crystal structure of near inverse spinel ensures more numerous defects to activate the near‐infrared (NIR) PersL of Fe3+. Fe3+‐doped MgGa2O4 displays the PersL band in the range of 600 to 900 nm and possesses a super‐long PersL duration time >15 h. The optical analysis and the calculation of density functional theory unravel that the near inverse spinel structure can lower the carrier transfer barriers to accelerate the formation of carrier trap states within the bandgap. Therefore, more numerous defects in this structure may participate in the trapping and de‐trapping process by comparison with the normal spinel configuration. These findings are expected to accelerate the development of new PersL materials through Fe3+ doping toward versatile biological applications in NIR window. [ABSTRACT FROM AUTHOR]

Mechanoluminescent (ML) materials featuring renewable mechanical‐to‐optical conversion have shown promising prospects in stress sensing, lighting, and display. However, the advancement in ML applications is being restrained by the obstacles in developing efficient ML materials and understanding the underlying ML mechanisms. Herein, a matrix evolution strategy to modulate the local microstructure and electronic environment around the luminescent activators is proposed, which not only supports the batch development of new ML materials but also provides a well‐connected platform for systematically revealing the mechanism of achieving efficient ML performance. The feasibility of the strategy is proved by constructing and evaluating a series of ML materials with matrix‐dependent luminescent properties in experimental‐theoretical collaboration. It is demonstrated that the construction of piezoluminescence is available in both non‐centrosymmetric and centrosymmetric matrices without being restricted by lattice symmetry. The inter‐electronic‐levels and shallow electron traps formed by activator doping enhance the electron recombination efficiency through tunneling and conduction band transfer pathways. The results are expected to accelerate the exploitation of ML material systems and to deepen the comprehensive apprehending of ML mechanisms, thereby guiding the rational design and widespread use of efficient ML materials. [ABSTRACT FROM AUTHOR]

Scintillators convert high‐energy radiation into visible luminescence and have been widely applied in various significant fields such as nuclear fusion monitoring, high‐energy particle physics, medical imaging, and geological exploration. The scalable fabrication of scintillating fiber with the desirable combination of uniform size, superior radiation blocking ability, and excellent thermal/radiation stability is a major challenge. Here, a template solidification strategy for fabrication of full‐inorganic and efficient scintillating fiber is presented. The strategy involves the direct solidification of high‐density scintillator melt in a softened silica tube, allowing for the continuous production of small and uniform scintillating fiber. The fabricated scintillating fiber can effectively attenuate radiation up to ≈118 times higher than what conventional silica fiber can. In addition, it exhibits good compatibility with commercial fiber. Using this scintillating fiber, a radiation fiber detector is constructed and its application for online radiation monitoring is demonstrated. [ABSTRACT FROM AUTHOR]

Enhanced broadband near-infrared luminescence has been observed in Bi-doped oxyfluoride glasses excited from UV to near-infrared regions with the addition of AgCl. Enhancement factors depend greatly on excitation wavelength and maximal enhancement factor over three times occurs at the excitation wavelength around 320, 640, and 800 nm. Ag species play dual functions. The mechanism of the enhancement is discussed in depth combing the energy transfer from Ag+, molecular-like, nonplasmonic Ag species, Bi3+ and Bi2+ to near-infrared bismuth active centers, and the redox reaction of Bi species with Ag species. These results offer a valuable way to enhance the near-infrared luminescence efficiency of Bi-doped glasses, and the dual functions of Ag species may also be employed to enhance luminescence of rare-earth and transition metal ions doped materials. [ABSTRACT FROM AUTHOR]

Here, we present three facile approaches to achieve wavelength tunable luminescence in the same host material with single dopant, i.e., by modulating doping level, preparation temperature, and atmosphere. Based on these methods, ultra-broadband tunable near-infrared luminescence with the largest full width at half maximum of about 500 nm covering the whole windows of optical communication has been obtained in bismuth-doped germanate glasses. Wavelength tunable luminescence is also observed with the change of excitation wavelength. Systematical strategy was followed to approach the physical origin of the near-infrared luminescence and we proposed that three different bismuth active centers contribute to the near-infrared luminescence in the germanate glasses. A comprehensive explanation for the tunable luminescence is given, combining the concentration, energy transfer, and chemical equilibrium of these active centers in the glasses. With the increase of melting temperatures and the increase of reducing extent of the preparation atmosphere, bismuth species transform from Bi3+ to Bi2+, Bi+, Bi0 and bismuth clusters, and then to bismuth colloid. Of particular interest is that red tunable luminescence was also observed by modulating doping level, preparation atmosphere, and excitation wavelength. Besides, the trapped-electron centers in germanate glasses can interact with bismuth species of high valence states leading to the formation of bismuth active centers of low valence states and the decrease of trapped-electron centers. This tunable ultra-broadband luminescence is helpful for a better understanding of the origin of the near-infrared luminescence in Bi-doped glasses and may have potential applications in varieties of optical devices. [ABSTRACT FROM AUTHOR]

Rare earth (RE) ions‐doped luminescent nanocrystals (NCs) with numerous unique advantages have attracted tremendous interest for the wide applications from science to engineering, yet suffering from the shortcoming of thermal quenching coming from surface organic ligands. We propose utilizing a facile acid‐base reaction to remove surface organic ligands introduced choosing carboxylic acids as stabilizing agent and weaken thermal quenching. The results showed that the acid‐base reaction displayed an outstanding cleaning effect. After acid‐treatment, most surface organic ligands were removed, and there was no influence on crystal structure and morphology of as‐prepared β‐NaYF4:Er3+ NCs. Meanwhile, with no surface organic ligands capping, β‐NaYF4:Er3+ NCs preferred brighter emission after thermal treatment, including up‐conversion (UC), near‐infrared (NIR), and mid‐infrared (MIR) emission. When calcined the acid‐treated β‐NaYF4:Er3+ NCs in different atmosphere, such as oxygen and reducing atmosphere (15%H2 + 85%N2), an unexpected enhancement of all emission bands in Er3+ was determined under phase transformation temperature, especially in oxygen atmosphere. Furthermore, all the fluorescence lifetimes of Er3+ also exhibited obvious extension. Our results supposed that the β‐NaYF4:Er3+ NCs have promising applications in safety ink, and the acid‐treatment by diluted hydrochloric acid is a general approach to remove deleterious organic ligands on NC surface further to weaken thermal quenching. [ABSTRACT FROM AUTHOR]

Monolithic luminescent glass‐ceramic is highly desirable for solid‐state lighting as it is stable and robust, while in practical light‐emitting devices only a thin luminescent layer is used for more efficient excitation and light extraction. In this paper, Mn2+‐doped glass and glass‐ceramic with the composition of 60SiO2‐8Na2O–20ZnO–12Ga2O3 were fabricated by the conventional melt‐quenching technique. We observe that the crystallization of α‐Zn2SiO4 nanocrystals takes place on the glass surface with controllable thickness after heat treatment. The glass samples show typical red emission peaking at λ = 620 nm that can be ascribed to the spin‐forbidden 4T1g(G) → 6A1g(S) transition of Mn2+ (d5) located in the octahedral coordination site of the glass host. After surface crystallization this red emission is retained and a new green emission at 528 nm is observed through the control of the crystallization temperature and duration, thus offering tunable emission characteristics promising for the lighting application. This change in the visible emission is interpreted in terms of the change of coordination state of Mn2+ from octahedral in a glass matrix to tetrahedral in the surface precipitated α‐Zn2SiO4 crystals. [ABSTRACT FROM AUTHOR]

Tm3+ doped and Tm3+/Yb3+ codoped lanthanum aluminum germanate (LAG) glasses are prepared by melt-quenching method and characterized optically. Based on the measurement of absorption spectrum, Judd–Ofelt intensity parameters (Ω2,Ω4,Ω6) are calculated. The radiation emission rates, branching ratios, and lifetimes of Tm3+ are calculated to evaluate the spectroscopic properties of Tm3+ in LAG glass. The infrared emission properties of the samples are investigated and the results show that the 1.8 μm emission can be greatly enhanced by adding proper amount of Yb3+ under the excitation of 980 nm. The energy transfer processes of Yb3+–Yb3+ and Yb3+–Tm3+ are analyzed, and the results show that Yb3+ ions can transfer their energy to Tm3+ ions with high efficiency and large energy transfer coefficient. [ABSTRACT FROM AUTHOR]

Bi, Ga, and Al codoped germanium glass was prepared and its optical properties were investigated by absorption, photoluminescence excitation (PLE), and photoluminescence spectra. Two active centers which occupy strong and weak crystal field environment are identified by using the PLE spectrum. The tunable and ultrabroadband luminescence properties are originated from electron transitions of these two active centers. Internal optical gain around 1300 and 1560 nm has been detected. The wavelength-dependent internal gains excited with 808 and 980 nm laser diodes show different characteristics, and the relative flat optical amplification can be realized by choosing 980 nm pumping. [ABSTRACT FROM AUTHOR]

Transparent Ni2+-doped MgO–Al2O3–TiO2–SiO2 glass ceramics were prepared, and the optical properties of Ni2+-doped glass ceramics were investigated. Broadband emission centered at 1320 nm was observed by 980 nm excitation. The longer wavelength luminescence compared with Ni2+-doped Li2O–Ga2O3–SiO2 glass ceramics is ascribed to the low crystal field hold by Ni2+ in MgO–Al2O3–TiO2–SiO2 glass ceramics. The change in optical signals at the telecommunication bands with or without 980 nm excitation was also measured when the seed beam passes through the bulk gain host. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report upconversion (UC) luminescence enhancement in LaBGeO5:Yb3+, Er3+ glass‐ceramics (GCs), surface crystallized glass‐ceramics (SCGCs) and ceramics compared with the as‐melt glass fabricated by the conventional melt‐quenching technique. Based on structural investigations, we find that the nucleation and crystallization of trigonal stillwellite LaBGeO5:Yb3+, Er3+ nanocrystals occur first at the glass surface before the following volume crystallization. The local site symmetry around rare earth (RE) ions which was evaluated using the Eu3+ ions as a probe together with Judd‐Ofelt theory calculations exhibits a clear increase with the devitrification of the glass. Consequently, complete crystallization of the glass leads to largest enhancement in the UC emissions of the LaBGeO5:Yb3+, Er3+ ceramics. We ascribe the enhancement of UC luminescence in the LaBGeO5:Yb3+, Er3+ GCs, SCGCs, and ceramics to the structural ordering and the improvement of site symmetry surrounding RE ions that minimizes the rate of nonradiative relaxation process. [ABSTRACT FROM AUTHOR]

Greater enhancement in upconversion (UC) luminescence was observed in the glass-ceramics (GCs) containing CaF2:Yb3+, Er3+ nanocrystals (NCs) compared with whose doped with LaF3:Yb3+, Er3+ NCs prepared by conventional melt-quenching technique followed by successive heat treatment. Our joint experimental and theoretical studies suggest the lager enhancement of UC emission in CaF2-GCs rather than of LaF3-GCs is associated with the difference in the microstructures, the crystal size, the local coordination environment around rare earth (RE) ions as well as the structural rigidity in the silicate region of the GCs. In addition, it was found that a more symmetric ligand field around RE ions in a smaller size crystal which distributed more homogeneously within the highest ordering silicate region favors stronger UC emission by facilitating the energy transfer process and minimizing the rate of non-radiative relaxation process. Our results may enrich our understanding about UC process in oxyfluoride GCs and provide a general picture for the photophysical processes that contribute to the UC in similar GCs systems. [ABSTRACT FROM AUTHOR]

Alkaline earth orthosilicates M2SiO4 (M = Ba, Sr and Ca) phosphors doped with Mn5+ ions have been prepared by the conventional solid-state reaction method. The crystal structures were verified by X-ray diffraction. By varying the host composition from Ba to Ca, the position shifting of photoluminescence emission bands corresponding to the 1E → 3A2 transition are induced by the increasing angular distortion and covalence. The nonradiative energy transfer becomes a dominant role in the photoluminescence process with substituting Ba2+ sites for smaller cations. The structural evolution and relevant luminescence mechanisms in (Ba1−xCax)2SiO4 phosphors also have been investigated in detail. It reveals that the chemical composition modification and structural variation can be an efficient approach to optimize the photoluminescence behaviors. [ABSTRACT FROM AUTHOR]

Abstract: An abnormal trap distribution and coordination geometry‐dependent multi‐band emission are discovered in chromium‐doped aluminates. The multi‐band and broadband persistent luminescence from 650–1100 nm peaking at 688 and 793 nm from Cr3+‐doped SrAl12O19 is systematically studied via structural and spectroscopic analysis. Solid state nuclear magnetic resonance allows the visualization of various coordination configurations in SrAl12O19, thus offering the possibility of tailoring the local geometry of the emission center to trigger the control of the spectral parameter. Deep tissue ex vivo and in vivo imaging in mice both demonstrate that multi‐band‐emissive SrAl12O19:Cr3+ shows superior, high‐quality near‐infrared (NIR) bio‐imaging in the biological transparency window compared to single band‐emissive (with emission only at 688 nm) SrAl2O4:Cr3+, although SrAl2O4:Cr3+ has a higher luminescent intensity and longer duration at 688 nm. Moreover, by measuring the thermoluminescence spectra the driving force of carrier release is discovered to be only from the deep trap (the depth is > 1 eV), which is different from the generally accepted shallow‐dependent afterglow‐emitting process. These findings pave the way for opening a vista of possible avenues for the enhancement of signal‐to‐noise ratio, the improvement of imaging quality, as well as the understanding of the trapping and de‐trapping process in long‐persistent phosphors. [ABSTRACT FROM AUTHOR]

The fabrication and near-infrared optoelectronic performance of the (Na YF4:Yb-Er)/Bi OI upconversion phosphor/semiconductor hybrid films are reported. The composite films were fabricated by a simple electro-deposition and successive ionic layer adsorption and reaction ( SILAR) method. We observed efficient upconversion emissions in the film of Na YF4:Yb-Er upon irradiation by near-infrared part of simulated sunlight, and the UC emission is drastically quenched in the composite film (Na YF4:Yb-Er)/Bi OI. More importantly, this composite film displays unusual negative photoresponse to near-infrared part of simulated sunlight when used in a standard electrochemical cell where the composite film serves as the photoanode. This result may pave the way for potential application of this hybrid films for the development of novel photovoltaic and infrared optoelectronic devices. [ABSTRACT FROM AUTHOR]

The development of doped photonic glass is of fundamental importance for various applications, including telecommunication, lasers, and photovoltaics. Despite the great advances in doping techniques, a long-standing barrier remains concerning how to gain better control over the properties of active dopants in disordered systems. Here, we provide a brief overview of recent progress on the engineering of the chemical environment and chemical state of dopants in glass by tuning the topological features, including sublattices and packing manner of the network. The methods allow us to finely tune the chemical state of active dopants over a wide range of length scales, from dispersed ions to aggregated clusters to nanoparticles, and also offer new opportunities to engineer the local crystal field around active dopants. This inherent structure-based strategy leads to intriguing optical phenomena such as tunable luminescence and notable enhancements in radiative transition probability. [ABSTRACT FROM PUBLISHER]

Improving upconversion luminescence efficiency of lanthanide-doped nanocrystals is always a hot topic for scientists because of its very important application in photonics, photovoltaics, biological imaging, security printing, and therapeutics. Two-color laser field has shown to be a well-established strategy to further improve the upconversion luminescence efficiency. Here, we first propose a two-color laser field combining the 850 and 980 nm lasers to improve the green and red upconversion luminescence efficiency in Er-doped NaYF nanocrystals. In this work, an important advantage for our strategy is that the population is directly pumped to the radiation energy level of the upconversion luminescence by a cooperation excitation process, but not the spontaneous decay from other higher energy levels, and so the higher luminescence enhancement efficiency can be obtained. These studies also provide a clear physical picture for the physical control mechanism of the upconversion luminescence efficiency improvement, which can pave a way to properly design the laser fields in the future study of upconversion luminescence generation and control. [ABSTRACT FROM AUTHOR]

Transfer of energy occurs endlessly in our universe by means of radiation. Compared to energy transfer (ET) in free space, in solid state materials the transfer of energy occurs in a rather confined manner, which is usually mediated by real or virtual particles, including not only photons, but also electrons, phonons, and excitons. In the present review, we discuss the recent advances in optical ET by resonance mediated with photons in solid materials as well as their nanoscale counterparts, with focus on the photoluminescence behavior pertaining to ET between optically active centers, such as rare earth (RE) ions. This review begins with a brief discussion on the classification of optical ET together with an overview of the theoretical formulations and experimental method for the examination of ET. We will then present a comprehensive discussion on the ET in practical systems in which normal photoluminescence, upconversion and quantum cutting resulted from ET involving metal ions, QDs, organic species, 2D materials and plasmonic nanostructures. Diverse ET systems are therefore simply categorized into cases of ion–ion interactions and non-ion interactions. Special attention has been paid to the progress in the manipulation of spatially confined ET in nanostructured systems including core–shell structures, as well as the ET in multiple exciton generation found in QDs and organic molecules, which behave quite similarly to resonance ET between metal ion centers. Afterwards, we will discuss the broad spectrum of applications of ET in the aforementioned systems, including solid state lighting, solar energy utilization, bio-imaging and diagnosis, and sensing. In the closing part, along with a short summary, we discuss further research focus regarding the problems and possible future directions of optical ET in solids. [ABSTRACT FROM AUTHOR]

ABSTRACT Red-emitting Mg4Nb2O9:Eu3+ phosphor is synthesized via a solid-state reaction method in air, and its crystal structure and luminescence are investigated. The phosphor can be excited efficiently by ~ 395 nm light, coupled well with a ~ 395 nm near-ultraviolet chip and emits red light at ~ 613 nm with sharp spectra due to 5 D0 → 7 F2 transition of the Eu3+ ion. Mg4Nb2O9:Eu3+ phosphor sintered at 1350 ºC shows Commission international de I'Eclairage (CIE) chromaticity coordinates of x = 0.6354, y = 0.3592, and is a potential red-emitting phosphor candidate for white light-emitting diodes (W-LEDs) under ~ 395 nm near-ultraviolet LED chip excitation. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) complex nanostructures on the surface of ZnO crystal are fabricated by the interference of three 800 nm fs laser beams. The 2D nanostructures exhibit a great enhancement of UV emission excited by infrared fs laser with central wavelengths ranging from 1,200 nm to 2,000 nm. We propose that the defect states in the band gap of 2D nanostructures induced by 800 nm fs laser ablation cause the great enhancement of UV emission. We make theoretical calculations and explain well with the experimental results. [ABSTRACT FROM AUTHOR]

Phosphors with an efficient yellow-emitting color play a crucial role in phosphor-converted white LEDs (pc-WLEDs), but popular yellow phosphors such as YAG:Ce or Eu2+-doped (oxy)nitrides cannot smoothly meet this seemingly simple requirement due to their strong absorptions in the visible range. Herein, we report a novel yellow-emitting LuVO4:Bi3+ phosphor that can solve this shortcoming. The emission from LuVO4:Bi3+ shows a peak at 576 nm with a quantum efficiency (QE) of up to 68 %, good resistance to thermal quenching ( T50 %=573 K), and no severe thermal degradation after heating-cooling cycles upon UV excitation. The yellow emission, as verified by X-ray photoelectron spectra (XPS), originates from the (3P0,3P1)→1S0 transitions of Bi3+. Increasing the temperature from 10 to 300 K produces a temperature-dependent energy-transfer process between VO43− groups and Bi3+, and further heating of the samples to 573 K intensifies the emission. However, it subsequently weakens, accompanied by blueshifts of the emission peaks. This abnormal anti-thermal quenching can be ascribed to temperature-dependent energy transfer from VO43− groups to Bi3+, a population redistribution between the excited states of 3P0 and 3P1 upon thermal stimulation, and discharge of electrons trapped in defects with a trap depth of 359 K. Device fabrication with the as-prepared phosphor LuVO4:Bi3+ has proved that it can act as a good yellow phosphor for pc-WLEDs. [ABSTRACT FROM AUTHOR]

Novel up-conversion ( UC) luminescent nanopowders, Sr2 CeO4: Yb3+, Ln3+ ( Ln = Er, Tm, Ho) were prepared with Pechini method. The Sr2 CeO4: Yb3+, Ln3+ ( Ln = Er, Tm, Ho) nanopowders had an orthorhombic crystal structure, and showed olive-like morphology with the length of about 260 nm and width of about 130 nm. Under 980 nm lazer excitation, the Sr2 CeO4: Yb3+/ Er3+, Sr2 CeO4: Yb3+/ Tm3+, and Sr2 CeO4: Yb3+/ Ho3+ nanophosphors exhibit strong green, blue, and green UC luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed. [ABSTRACT FROM AUTHOR]

In this manuscript, we report an ultrabroadband luminescence covering the whole 1000-1800 nm in [ABSTRACT FROM AUTHOR]

Searching for an efficient non rare earth-based oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm and unexcitable by green light, is essential for the development of warm white light emitting diodes ( WLEDs). Here, we report a promising and orderly-layered candidate: Sr4 Al14 O25: Mn4+ with CIE color coordinates (0.722, 0.278). It has higher luminescence efficiency particularly upon blue excitation and is much cheaper than the commercial red phosphor 3.5 MgO·0.5 MgF2· GeO2: Mn4+ ( MMG: Mn4+). In sharp contrast to Eu2+-doped (oxy)nitrides, the phosphor can be synthesized by a standard solid-state reaction at 1200°C in air. The effects of flux boron content, environment, and preparation temperature, sintering dwelling time as well as Mn concentration have been systematically investigated for establishing the optimal synthesis conditions. The low temperature emission spectra reveal that there are at least three types of Mn4+ ions in Sr4 Al14 O25: Mn4+ due to the substitution for the distorted octahedral Al3+ sites. The AlO6 layers where Mn4+ prefers to reside are well separated from one another by AlO4 tetrahedra in one dimension parallel to axis a. This scenario can efficiently isolate Mn4+ ions from local perturbations, thereby enabling the high efficiency of luminescence. The energy transfer rates and mechanism are discussed. [ABSTRACT FROM AUTHOR]

In this work, the luminescent properties of Sb3+/ Mn2+ codoped 60 P2 O5-40 MgO glass are presented. White light photoluminescence combining blue and orange-red light was observed under ultraviolet light excitation. The emission spectra showed that the blue emission intensity of Sb3+ decreased significantly whereas the red emission intensity of Mn2+ increased with the increasing concentration of Mn2+ ions. Meanwhile, by maintaining the concentration of MnO (2.0 mol%) and increasing concentration of Sb2 O3, both the blue emission and red emission were enhanced remarkably. The energy transfer from Sb3+ to Mn2+ ions via the dipole-quadrupole interaction was confirmed. [ABSTRACT FROM AUTHOR]

We report on the absorption, static, and transient luminescence spectra of Sm3+-doped glasses. The dependences between absorption and emission cross sections as well as between luminescence quantum efficiencies and Sm3+ doping concentration are examined. The large stimulated absorption cross section and emission cross section combined with the long fluorescent lifetime make phosphate glasses doped with Sm3+ promising material for visible fiber lasers. Moreover, ΔT(Tx − Tg) of these glasses is about 290 °C, which guarantees their thermal stability against crystallization during the fiber drawing process. [ABSTRACT FROM PUBLISHER]

Cr3+-doped LiInSiO4 phosphors were prepared by a solid-state reaction method. X-ray diffraction measurement was carried out for crystalline phase identification. Absorption, photoluminescence, excitation, and time-resolved spectra were measured to investigate the optical properties of the phosphors. Two broadband near-infrared emissions centered at 920 and 1172 nm were observed. Time-resolved spectra show that the emission at 1172 nm decays more quickly than the emission at 920 nm. The electron spin resonance spectra exhibit a broad resonance signal at g = 1.96 because of exchange-coupled Cr3+ pairs. The value of Dq/B for low and intermediate crystal fields was evaluated. We suggest that Cr3+ incorporated into different octahedral sites of the crystal is responsible for the different near-infrared luminescence. [ABSTRACT FROM AUTHOR]