Dual heterogeneous interfaces enhance X-ray excited persistent luminescence for low-dose 3D imaging.

Lanthanide-doped fluoride nanoparticles (NPs) showcase adjustable X-ray-excited persistent luminescence (XEPL), holding significant promise for applications in three-dimensional (3D) imaging through the creation of flexible X-ray detectors. However, a dangerous high X-ray irradiation dose rate and complicated heating procedure are required to generate efficient XEPL for high-resolution 3D imaging, which is attributed to a lack of strategies to significantly enhance the XEPL intensity. Here we report that the XEPL intensity of a series of lanthanide activators (Dy, Pr, Er, Tm, Gd, Tb) is greatly improved by constructing dual heterogeneous interfaces in a double-shell nanostructure. Mechanistic studies indicate that the employed core@shell@shell structure could not only passivate the surface quenchers to lower the non-radiative relaxation possibility, but also reduce the interfacial Frenkel defect formation energy leading to increase the trap concentration. By employing a NPs containing flexible film as the scintillation screen, the inside 3D electrical structure of a watch was clearly achieved based on the delayed XEPL imaging and 3D reconstruction procedure. We foresee that these findings will promote the development of advanced X-ray activated persistent fluoride NPs and offer opportunities for safer and more efficient X-ray imaging techniques in a number of scientific and practical areas.

Improved optical properties of phosphors-in-glass through the optimal size distribution of glass powder.

White-light diodes (WLEDs) are widely used in high-brightness applications owing to their outstanding advantages. However, current methods for preparing commercial WLEDs significantly deteriorate their optical properties and limit their use in high-power applications. To address this, inorganic materials, such as phosphor-in-glass (PiG), have been recently investigated as practical alternatives. In this study, a series of high-efficiency white-emitting PiG samples were prepared by mixing silicate glass powders with different particle size distributions and different concentrations of Y3Al5O12:Ce3+ (YAG:Ce3+) phosphors. The microstructure, transmittance, and photoluminescence properties of PiG were investigated. When the glass powder with the particle size ranges of 75-150 and 30-48 µm were mixed, at a ratio of 94 : 6, a silicate glass with a thickness of 0.8 mm and a maximum transmittance of 75% in the visible range was obtained. Under excitation with a 450 nm blue-light laser diode, PiG produced white light with a total luminescence efficiency of 194.64 lm W-1 and a total luminous flux of 623.9 lm. These results demonstrate that the optical performance of PiG can be effectively adjusted by adjusting the particle size distribution of silicate glass powder and the mixing concentration of the YAG:Ce3+ phosphor, thereby providing a tuning pathway for smart white-light devices.

Manipulation of time-dependent multicolour evolution of X-ray excited afterglow in lanthanide-doped fluoride nanoparticles.

External manipulation of emission colour is of significance for scientific research and applications, however, the general stimulus-responsive colour modulation method requires both stringent control of microstructures and continously adjustment of particular stimuli conditions. Here, we introduce pathways to manipulate the kinetics of time evolution of both intensity and spectral characteristics of X-ray excited afterglow (XEA) by regioselective doping of lanthanide activators in core-shell nanostructures. Our work reported here reveals the following phenomena: 1. The XEA intensities of multiple lanthanide activators are significantly enhanced via incorporating interstitial Na+ ions inside the nanocrystal structure. 2. The XEA intensities of activators exhibit diverse decay rates in the core and the shell and can largely be tuned separately, which enables us to realize a series of core@shell NPs featuring distinct time-dependent afterglow colour evolution. 3. A core/multi-shell NP structure can be designed to simultaneously generate afterglow, upconversion and downshifting to realize multimode time-dependent multicolour evolutions. These findings can promote the development of superior XEA and plentiful spectral manipulation, opening up a broad range of applications ranging from multiplexed biosensing, to high-capacity information encryption, to multidimensional displays and to multifunctional optoelectronic devices.

Narrow-band Rb1-yKyNa3(Li3SiO4)4:Eu2+(0 ≤ y ≤ 1) cyan-blue phosphors for full-spectrum white LEDs.

A series of Rb1-yKyNa3(Li3SiO4)4:Eu2+(0 ≤ y ≤ 1) phosphors were successfully synthesized through a high-temperature solid-state reaction. The introduction of K+ into the RbNa3(Li3SiO4)4:Eu2+ phosphor to partially or completely replace Rb+ allows the emission spectrum to be modulated from blue (λ = 473 nm, FWHM = 22.5 nm) to a narrow cyan band (λ = 485 nm, FWHM = 21.1 nm). As the K+ ion content increases, the space group of the phosphor evolves from I4/M to I41/A. The complete replacement of Rb+ by K+ results in the KNa3(Li3SiO4)4:Eu2+ cyan phosphor, which shows excellent thermal stability (the comprehensive emission loss is only 8% at 150 °C) and can be used to fill the cyan light gap in white LED devices. By adding the KNa3(Li3SiO4)4:Eu2+ cyan phosphor in packaging with yellow and red phosphors, the color rendering index is increased from 90.2 to 97.1 and the correlated color temperature improved to 3658 K. These results indicate that the cyan phosphor has important application value in full-spectrum white LEDs.

Amplifying Upconversion by Engineering Interfacial Density of State in Sub-10 nm Colloidal Core/Shell Fluoride Nanoparticles.

Achieving bright photon upconversion under low irradiance is of great significance and finds many stimulating applications from photovoltaics to biophotonics. However, it remains a daunting challenge to significantly intensify upconversion luminescence in small nanoparticles with a simple structure. Herein, we report the amplification of photon upconversion through engineering interfacial density of states between the core and the shell layer in sub-10 nm colloidal rare-earth ions doped fluoride nanocrystals. Through tuning of the metal cations in the shell layer of alkaline-earth-based core/shell nanoparticles, both the interfacial phonon frequency and the density of state are evidently decreased, resulting in the luminescence intensification of up to 8224 times. The generality of this upconversion enhancement strategy has been verified through expansion of this approach to alkali-based core/shell nanoparticles. The engineering of photon density of state in such core/shell nanoparticles enables dynamic display and high-level security information storage.

A study of negative-thermal-quenching (Ba/Ca)AlSi5O2N7:Eu2+ phosphors.

Phosphor is an important part of the new generation of light-emitting diodes (LEDs), which requires high luminous intensity and high-temperature resistance. In this study, a series of excellent (Ba1-x-yCax)AlSi5O2N7:yEu2+ phosphors was developed, which were synthesized by a high-temperature solid-state reaction in a reducing atmosphere. In addition, the crystallinity and luminescence intensity of the samples could be enhanced by some amount of Ca2+ substitution. The luminescence intensity was the highest when the Eu2+ concentration reached 0.06. Furthermore, the thermal stability of the luminescence was studied in detail. The results were satisfactory, showing that the luminescence intensity of the (Ba1-xCax)AlSi5O2N7:Eu2+ phosphors exhibited unique negative-thermal-quenching characteristics both at high (273-473 K) and low (4-273 K) temperatures. And the phosphor combined with UV LED chip and red phosphor Sr2Si5N8:Eu2+ can achieve a CRI of 90.4 in white LED application which indicated the (Ba1-xCax)AlSi5O2N7:Eu2+ phosphor has potential in LED applications.

Highly Efficient NaGdF4:Ce/Tb Nanoscintillator with Reduced Afterglow and Light Scattering for High-Resolution X-ray Imaging.

Scintillation-based X-ray excited optical luminescence (XEOL) imaging shows great potential applications in the fields of industrial security inspection and medical diagnosis. It is still a great challenge to achieve scintillators simultaneously with low toxicity, high stability, strong XEOL intensity, and weak afterglow as well as simple device processibility with weak light scattering. Herein, we introduce ethylenediaminetetraacetate (EDTA)-capped NaGdF4:10Ce/18Tb nanoparticles (NPs) as a highly sensitive nanoscintillator, which meets all of the abovementioned challenges. These NPs show comparable XEOL intensity to the commercial CsI (Tl) single crystal in the green region. We propose a mechanism that involves a new electron-captured path by Ce3+ ions and the promotion of energy migration from a trap center to surface quenchers via a Gd3+ sublattice, which greatly reduces the population in traps to produce significant reduction of afterglow. Moreover, by employing an ultrathin transparent NaGdF4:10Ce/18Tb film (0.045 mm) as a nanoscintillator screen for XEOL imaging, a high spatial resolution of 18.6 lp mm-1 is realized owing to the greatly limited optical scattering, which is superior to the commercial CsI (TI) scintillator and most reported lead halide perovskites. We demonstrate that doping Ce3+ ions can greatly limit X-ray-activated afterglow, enabling to use an ultrathin transparent fluoride NP-based nanoscintillator screen for high-quality XEOL imaging of various objects such as an electronics chip and biological tissue.

Fabrication of large size individual octahedral tungsten oxide hydrate and Au NPs as SERS platforms for sensitive detection of cytochrome C.

Surface-enhanced Raman scattering (SERS) has attracted much attention with its powerful trace detection and analysis capabilities, especially biological and environmental molecules. However, building a protein SERS detection platform based on semiconductor devices is a huge challenge. Herein, through the synergy of NH3 and nickel foam, a large-sized semiconductor tungsten oxide hydrate platform (WOHP) was synthesized. The crystal plane of a single WOHP particle is larger than the excitation spot. As a SERS substrate, WOHP can make full use of the excitation light without destroying the structure during the protein molecules detection process. Through the synergy of WOHP and Au NPs, the enhancement factor is 1.5 × 104. Raman peaks of WOHP can be used as references for the detection of typical protein cytochrome C (Cyt C). As the Cyt C concentration decreases, the ICyt C/IWOHP ratio decreases, and the signal can still be obtained when the concentration is as low as 5 × 10-9 mol L-1. More importantly, the method does not affect the catalytic activity of Cyt C and can be applied to the detection of Cyt C concentration in serum.

Integrating Positive and Negative Thermal Quenching Effect for Ultrasensitive Ratiometric Temperature Sensing and Anti-counterfeiting.

Fluorescence intensity ratio-based temperature sensing with a self-referencing characteristic is highly demanded for reliable and accurate sensing. Although enormous efforts have been devoted to explore high-performance luminescent temperature probes, it remains a daunting challenge to achieve highly relative sensitivity which determines temperature resolution. Herein, we employ a novel strategy to achieve temperature probes with ultrahigh relative sensitivity through integrating both positive and negative thermal quenching effect into a hydrogel. Specifically, Er3+ ions show evidently a positive thermal quenching effect in Yb/Er:NaYF4@NaYF4 nanocrystals while Nd3+ and Tm3+ ions in a Yb2W3O12 bulk exhibit prominently a negative thermal quenching effect. With elevating temperature from 313 to 553 K, the fluorescence intensity ratio of Er (540 nm) to Nd (799 nm) and Tm (796 nm) to Er (540 nm) is significantly decreased about 1654 times and increased about 14,422 times, respectively. The maximum relative sensitivity of 15.3% K-1 at 553 K and 23.84% K-1 at 380 K are achieved. The strategy developed in this work sheds light on highly sensitive probes using lanthanide ion-doped materials.

Coefficient effect of rare earth and metal ions in phosphor combined glass materials for a wide color gamut display.

The surface plasmon resonance (SPR) of metal nanostructures is known to affect the optical properties of solid luminescent materials. Ag nanoparticles were first used to obtain a wider color gamut in rare-earth-doped phosphor-in-glass for application as color filters for white light emitting diodes. The existence of Ag nanocrystallites at nanometer scale and the independent integrity of the phosphor luminescence center in the amorphous glass environment were demonstrated. Using UV-Vis spectroscopy, the localized SPR absorption band was observed at 480 nm, and the optical properties of the nanostructures were found to be dependent on the annealing temperature. Hence, an expansion of the color gamut from 79.07% to 93.31% was realized by the coefficient effect of Nd3+ active ions and Ag nanoparticles. These results suggest that Nd3+-ion-co-doped phosphor-in-glass modified by Ag nanoparticles could be potentially applied as a novel optical material with a wide color gamut.

Ultrabroadband Tuning and Fine Structure of Emission Spectra in Lanthanide Er-Doped ZnSe Nanosheets for Display and Temperature Sensing.

Realizing multicolored luminescence in two-dimensional (2D) nanomaterials would afford potential for a range of next-generation nanoscale optoelectronic devices. Moreover, combining fine structured spectral line emission and detection may further enrich the studies and applications of functional nanomaterials. Herein, a lanthanide doping strategy has been utilized for the synthesis of 2D ZnSe:Er3+ nanosheets to achieve fine-structured, multicolor luminescence spectra. Simultaneous upconversion and downconversion emission is realized, which can cover an ultrabroadband optical range, from ultraviolet through visible to the near-infrared region. By investigating the low-temperature fine structure of emission spectra at 4 K, we have observed an abundance of sublevel electronic energy transitions, elucidating the electronic structure of Er3+ ions in the 2D ZnSe nanosheet. As the temperature is varied, these nanosheets exhibit tunable multicolored luminescence under 980 and 365 nm excitation. Utilizing the distinct sublevel transitions of Er3+ ions, the developed 2D ZnSe:Er3+ optical temperature sensor shows high absolute (15.23% K-1) and relative sensitivity (8.61% K-1), which is superior to conventional Er3+-activated upconversion luminescent nanothermometers. These findings imply that Er3+-doped ZnSe nanomaterials with direct and wide band gap have the potential for applications in future low-dimensional photonic and sensing devices at the 2D limit.

Reversible modification of ultra-broadband luminescence in transparent photonic materials through field-induced nanoscale structural transformation.

The development of integrated multifunctional materials with transparent characteristics meets the requirements of optoelectronics and communication. The coupling of stimuli-responsive materials has become a frequently considered strategy. Experimentalists not only search for photonic materials with excellent physical and chemical properties, but also pursue precise and reversible spectral modification. In this study, the luminescent center Ni2+ is artificially introduced into the transparent LiNbO3 nanoferroelectric photonic materials. The Ni2+ ion-based transparent photonic materials exhibit novel complete ultra-broadband emission in the whole near-infrared region. Until now, the ultra-broadband emission was realized by codoping of several active doping ions. In addition, the emission intensity and wavelength of the luminescent center are modified accurately and reversibly by field-induced nanoscale structural transformation. The Ni2+ ion-based transparent nanoferroelectric photonic materials provide an easy way to develop tunable lasers and ultra-broadband optical amplifiers.

Ln3+ doped phosphor-in-glass: A new choice of color filter for wide-color gamut white light-emitting diodes.

Phosphor-in-glass (PiG) is a novel fluorescent color conversion material that is an excellent choice for preparing wide-color gamut white LEDs due to its excellent thermal stability, high efficiency and facile preparation process. To the best of our knowledge, this paper is the first to widen the color gamut of the white LED from 77.33% to 92.02% by doping the PiG substrate with two kinds of lanthanide ions: Er3+ and Nd3+. The low sintering temperature and suitable preparation process has ensured the phosphor and glass become compounded independently together while still exhibiting good luminescence performance; this has been demonstrated via X-ray diffraction and field emission scanning electron microscopy. The influence of doping the host glass with Ln3+ ions has been explored, specifically considering the effects on the color gamut, the color coordination, the correlated color temperature and the color rendering index. The results presented herein have demonstrated that the Er3+/Nd3+-doped PiG is a promising candidate as a color filter in the domain of wide-color gamut white LED.

Efficient Er3+:4I11/2 → 4I13/2 radiative transition regulated by optimizing the sensitization mechanism.

A series of fluorophosphates glass codoped with active Er3+ ions and sensitizing ions of different systems were prepared to systematically study their sensitization effect in order to obtain efficient MIR luminescence. Differential scanning calorimetry curve indicates the favorable thermal stability of the glass host. A comprehensive analysis of the sensitization mechanism is given based on the synthesis considering the position and intensity of fluorescence emissions together with the lifetime of Er3+:4I13/2 active level. The results show two positive sensitization effects: the eliminating effect to the lower laser level of Er3+ active ions represented by Pr3+ ions reducing the lifetime of 4I13/2 energy level to a great extent; and improving the absorption efficiency of pumping source sensitized by Yb3+ ions. The paper has provided a mental knowledge for sensitization mechanism in rare earth multi-doped materials together with the aiming of promoting the MIR luminescence of Er3+ ions.

Oxychloride glass with low phonon energy as a choice for infrared laser materials.

Recently, rare-earth-doped infrared (IR) luminescent glasses have drawn massive attention due to their potential applications in military, medical, and communications fields. In this Letter, we present a system of oxychloride Si-Ge-O-Cl glasses, suitable for rare-earth doping, which has been developed as a new, to the best of our knowledge, choice for IR luminescent materials. Raman spectra show a looser glass network because of the decreased phonon energy and density compared to the one in heavy-metal oxide glasses. The enhanced luminescence from the visible to the IR region has been obtained with a beneficial fluorescence decay time. The spectroscopy results indicate that the system of Si-Ge-O-Cl glasses may be a promising candidate for application in infrared laser materials with enhanced luminescence.

Enhanced UC and IR luminescence properties regulated by tight network structure in multicomponent glasses.

Lanthanide-doped optical functional glasses have received substantial attention in recent years owing to their excellent upconversion (UC) and infrared (IR) performance pumping when used in a semiconductor laser. In this study, the luminescence properties of Ho3+ ions were improved through the design of components used to modulate the microenvironment of the glass. To the best of our knowledge, this is a novel approach to enhancing the UC and IR emissions, and results in up to more than 130% improvement by regulating a tight network glass structure. Herein, the specific preparation design and investigations into the thermal, structural and luminescence properties are described, the results of which indicate that such ZnO-modified germanosilicate (SG-Zn) multicomponent glasses are promising candidates in the fields of biological security marking, optical communication, and 3D volumetric displays.

Broad Mid-Infrared Luminescence in a Metal-Organic Framework Glass.

Metal-organic framework (MOF) glasses are a newly discovered family of melt-quenched glasses. Despite considerable progress in understanding the nature of MOF glasses, their photonic functionalities have not been found so far. Here, we report on the first breakthrough regarding the photonic functionalities of MOF glasses, that is, finding of the luminescence in melt-quenched MOF glasses. The finding was achieved on a zeolitic imidazolate framework (ZIF) series, that is, the ZIF-62 series: Zn1-x Co x (Im)1.7(bIm)0.3, x = 0, 0.1, and 0.5, where Co substitutes Zn in ZIF-62 forming single-phased solid solutions. Remarkably, we observed broadband mid-infrared (Mid-IR) luminescence (in the wavelength range of 1.5-4.8 µm) in both the crystalline and amorphous solid solutions. The intensity of the luminescence in ZIF glass is gradually enhanced by increasing the level of Co concentration. The observed Mid-IR emission originates from d-d transition of Co ions. The discovery of the luminescence in ZIF-62 glass may pave the way toward new photonic applications of bulk MOF glasses.

Enhancing the luminescence performance in germanosilicate glasses controlled by ZnF2.

Rare-earth-doped optical functional glasses have attracted great interest for their excellent luminous performance in the applications of optical communications and biomedical systems. To the best of our knowledge, it is demonstrated for the first time that more than seven times' enhancement of luminescence performance in the mid-infrared region (MIR) has been obtained in germanosilicate glasses controlled by ZnF2. Larger absorption and emission cross sections of the Ho3+: I65→I75 transition indicate that this kind of germanosilicate-zinc glass may provide high gain as a good medium for an efficient 2.85 µm laser system.

Tuning the micro-structure of germanosilicate glass to control Bi0/Bi+ and promote efficient Ho3+ fluorescence.

Bi can exist in a variety of chemical states (with varying ionic charges) and the microstructure of the glass surrounding the ions can be engineered to manipulate the chemical state. In this work, efficient enhancement of Ho3+ emission is observed with the change in local glass environment around Bi by adding Al2O3 to multi-component germanosilicate glass. In this multi-component glass, Al3+ can form tetrahedral AlO4 by accepting the non-bridging oxygen (NBO) and then, the addition of the AlO4-tetrahedron to the glass network facilitates the diffusion of alkali metals. Hence, Al2O3 decreases the Ba2+-rich domain and is conducive to the existence of Bi ions that are at low valence state. Moreover, the emission spectra indicate high efficiency energy transfer (ET) derived from NIR emission centers (Bi0/Bi+) located in close proximity to the Ho3+ ions. These results indicate that the optimized fluorescence of Ho3+ for optical fiber laser can be achieved by adjusting the local structure of the host glass.

Controllable structural tailoring for enhanced luminescence in highly Er3+-doped germanosilicate glasses.

Higher concentrations of rare earth (RE) ions in glass materials would be favorable for the output of single-frequency fiber lasers. In this Letter, we adjusted the topological structure of glass networks through controlling the numbers of non-bridging oxygens (NBOs) and bridging oxygens (BOs) by tuning the composition of the glasses, hence increasing the RE doping concentration of germanosilicate glasses. The increased flexibility of the glass networks favors the distribution of clusters of RE ions to decrease fluorescence quenching, which was validated by both our experimental and theoretical results. To the best of our knowledge, for the first time, a highly Er3+-doped (up to 7 mol. %) heavy metal oxide glass was fabricated without quenching by tuning the components of the glass. In addition, we have demonstrated an approach to enhance the fluorescence properties of heavily RE-doped glass materials by tailoring network topology.