Bright Green Emission Research Articles

The preparation of novel AIE fluorescent microspheres by dispersion polymerization

ABSTRACT An approach to prepare monodisperse polystyrene microspheres with aggregation-induced emission (AIE) characteristics has been developed which shows promising applications in fluorescence-encoding. The micron-sized, monodisperse polystyrene microspheres with AIE molecules were perfectly synthesized by two-stage dispersion polymerization. Fluorescent AIE monomer was synthesized by Suzuki reaction, confirmed by nuclear magnetic resonance (NMR). These AIE fluorogens (AIEgens) exhibited unique properties such as bright green emission in solid state and increased emission in tetrahydrofuran (THF) solution with the increase of water content. The influence of the AIE molecules concentration to microspheres synthesis was well investigated. The reaction conditions were optimized to obtain the functional polystyrene microspheres with a size distribution around 3%. The novel microspheres were characterized by scanning electron microscopy (SEM), confocal fluorescence microscope and flow cytometry. According to these results, two-stage dispersion polymerization was proved to be an efficient pathway for the preparation of AIE fluorescent and functionalized microspheres, which could be used in many biomedical industries.

Enhanced bright green luminescence from GdOF:Ho3+ up-conversion phosphor via Yb3+ doping

In this paper, a series of GdOF-based green phosphors doped with Ho3+ and Yb3+ ions was prepared by a simple co-precipitation method. The crystal structures and optical properties were investigated in detail. The intensity of the emission of GdOF:Yb3+,Ho3+ phosphors is enhanced by the effective energy transfer from Yb3+ to Ho3+, and the optimal luminescence is achieved with the Ho3+ doping amount of 0.1 mol% as well as Yb3+ doping amount of 5 mol%. Tunable UC emission of samples is achieved by adjusting the doping concentration of Ho3+ or Yb3+. The purity of the green UC emission is further improved by enhancing the excitation pumping power. In addition, logarithmic functions of green, red and near-infrared radiation intensities were calculated versus logarithmic function of pump power for further study. A possible UC luminescence mechanism between Yb3+ and Ho3+ is discussed based on power-dependent UC luminescence spectrum and decay lifetimes. These results suggest that GdOF:Yb3+,Ho3+ phosphors with bright and high-purity green UC emission have potential applications in the fields of bioimaging, display and illumination.

Two-Dimensional Layered Organic-Inorganic Hybrid Perovskite Thin-Film Fabrication by Langmuir-Blodgett and Intercalation Techniques.

We demonstrate the formation of a well-organized thin film of two-dimensional (2D) layered (C18H37NH3)2PbI4 hybrid perovskite by immersing octadecyl amine (ODA) Langmuir-Blodgett (LB) films in an aqueous solution of PbI2/HI. The immersed films exhibit a sharp absorption band at 486 nm (2.55 eV), which is assigned to the excitonic absorption. The film exhibits a bright green emission under ultraviolet light at room temperature. The photoluminescence spectrum has a distinct peak at 497 nm (2.49 eV) and is a mirror image of the absorption spectrum. X-ray diffraction (XRD) analyses reveal that the film has a bilayer-like structure with a d-spacing of 6.4 nm, which is equal to that of a (C18H37NH3)2PbI4 perovskite single crystal with a quantum well (QW) structure. Only intense peaks of the (0 0 l) (l = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24) reflections are observed in the out-of-plane XRD pattern, indicating that the c axis is vertically oriented with respect to the substrate surface, and the orientational order is remarkably high. Fourier transform infrared spectroscopy reveals that the ODA molecules are protonated in the PbI2/HI solution. These results suggest that the nitrogen atoms of the ODA molecules in the film are protonated in the PbI2/HI solution, and then, inorganic layers of the PbI6 octahedra are intercalated in the alkyl ammonium film to neutralize the positive charge and form a QW structure. Fluorescence microscopy observation reveals that the 2D layered (C18H37NH3)2PbI4 film has a relatively uniform surface, reflecting the well-organized layered structure of the base material (ODA LB film). Because the intercalation process can be applied to various metal cations and halogen anions, we believe that the proposed technique will aid in the development of highly efficient 2D layered organic-inorganic hybrid perovskite materials.

Near-unity quantum yield in zero-dimensional lead-free manganese-based halides for flexible X-ray imaging with high spatial resolution

Low-dimensional luminescent lead-free metal halides have received substantial attention due to their unique optoelectronic properties. Among them, zero-dimensional (0D) manganese (II)-based metal halides with negligible self-absorption have emerged as potential candidates in X-ray scintillators. Herein, we for the first time report a novel lead-free (TBA)2MnBr4 single crystal synthesized via a facile solvent evaporation method. In this crystal, [MnBr4]2− units are isolated by large TBA+ organic cations, resulting in a unique 0D structure. The prepared manganese-based crystals exhibit a bright-green emission centered at 512 ​nm with a high photoluminescence quantum yield (PLQY) of 93.76% at room temperature, originating from the 4T1–6A1 transition of Mn2+. Apart from their outstanding optical performance, the crystals also show excellent stability and can maintain 94.4% of the initial PLQY even after being stored in air for 90 days. Flexible (TBA)2MnBr4 films prepared as X-ray imaging scintillators exhibit a low detection limit of 63.3 nGyair/s, a high light yield of 68000 ​ph/MeV, and a high spatial resolution of 15.4 ​lp/mm. Thus, this work not only enriches the family of lead-free metal halides but also expands the application of manganese (II)-based halides in flexible X-ray scintillators.

Upconversion luminescence and optical thermometry of Gd3BWO9: Yb3+, Er3+ phosphors

Rare earth upconversion (UC) luminescent materials have important application prospect in the field of optical thermometry due to the unique fluorescence properties. To search for new and efficient UC luminescent materials for optical temperature measurement, a series of Gd3BWO9: Yb3+, Er3+ UC phosphors were prepared through a high temperature solid-state reaction process. X-ray diffraction data show that all of the Gd3BWO9: Yb3+, Er3+ phosphors have pure Gd3BWO9 crystal phase. Under the excitation of 980 ​nm pump laser, all of the Gd3BWO9: Yb3+, Er3+ phosphors exhibit bright green emission at 522 ​nm and 543 ​nm. The UC luminescence mechanism and energy transfer (ET) processes were revealed by studying the power dependency of the UC emission intensities, and the green emission lifetimes of 4S3/2-2H15/2 were also measured to prove the existence of ET between Yb3+ and Er3+ ions. Moreover, the optical thermometry performance of Gd3BWO9: 0.20 ​Yb3+, 0.02 Er3+ was investigated by using fluorescence intensity ratio techniques. At 303 ​K, the relative sensitivity of phosphor is 0.94% K−1. The results manifest that Yb3+- Er3+ co-doped Gd3BWO9 phosphors can be used in optical temperature measurement.

Multiple anti-counterfeiting strategy by integrating up-conversion, down-shifting luminescence, phosphorescence and photochromism into NaYTiO4: Bi/Er phosphors

• The micron phosphors NaYTiO 4 : Bi/Er were prepared by solid state reaction. • NaYTiO 4 : Bi/Er phosphors possess considerable up-conversion, down-shifting luminescence, phosphorescence and photochromism performances. • A novel strategy for multiple anti-counterfeiting is proposed and successfully executed based on NaYTiO 4 : Bi/Er phosphors. • NaYTiO 4 : Bi/Er phosphors can be a great candidate for high-security-level anti-counterfeiting application. With the rapid development of science and technology, the high-security-level anti-counterfeiting technique is essential for ensuring property or information security. In this work, we prepared micron NaYTiO 4 : Bi/Er (NYT: Bi/Er) phosphors with integrating up-conversion (UC) photoluminescence, down-shifting (DS) emission, phosphorescence and photochromism (PC) performances for advanced multiple anti-counterfeiting application. Owing to the abundant energy levels of Er 3+ ions, the UC and DS luminescence behaviors are anticipated. Specifically, the yellow-green emission of Er 3+ ions can be observed upon 980 nm excitation, and the bright green emission is demonstrated under 281 or 254 nm excitation due to the energy transitions of Er 3+ ions and the energy transfer process from Bi 3+ to Er 3+ ions. Besides, the introduction of Bi 3+ ions generates defect levels in the matrix and thus leads to phosphorescence. Furthermore, the repeatable PC performance could be triggered by the 365 nm irradiation and vanished with 450 nm illumination or thermal stimulation. To verify the practical usability of NYT: Bi/Er phosphors on anti-counterfeiting applications, some experiments are designed and successfully executed. It is believed that the NYT: Bi/Er phosphors can be a promising candidate for high-security-level multiple anti-counterfeiting.

The synthesis of Er3+/Yb3+/K+ triple-doped NaYF4 phosphors and its high sensitivity optical thermometers at low power

Optical Thermometry is popular among researchers because of its non-contact, high sensitivity, and fast measurement properties. In the present experiment, Er3+/Yb3+/K+ co-doped NaYF4 nanoparticles with different K+ concentrations were synthesized by solvothermal method, and the samples showed bright upconversion green emission under the excitation of a 980 nm laser. The powder X-ray diffractometer and transmission electron microscope were used to characterize the crystal structure and its surface morphology, respectively. The spectral characteristics of nanoparticles with K+ doping concentration from 10% to 30% (Molar ratio) were investigated by fluorescence spectroscopy, and it was observed that the fluorescence intensity reached the maximum at the K+ concentration of 20%, after which the intensity weakened when the K+ content continued to increase. According to the dependence between the luminescence intensity of the sample and the laser power density and fluorescence lifetime, the intrinsic mechanism was carefully investigated. Temperature-dependent spectra of the samples were recorded in the temperature range of 315–495 K， and the maximum values of absolute sensitivity (Sa) and relative sensitivity (Sr) were measured at 0.0041 K−1 (455 K) and 0.9220%K−1 (315 K). The experimental results show that K+/Er3+/Yb3+ triple-doped NaYF4 green fluorescent nanoparticles (GFNs) have good prospects for applications in display devices, temperature sensing, and other fields.

Design and electrospinning synthesis of SrF2:Er3+/Yb3+ unidimensional nanostructural materials with tunable upconverting fluorescence

In order to develop new morphology and properties of up-converting fluorescent materials, SrF2:Er3+/Yb3+ up-converting fluorescent unidimensional nanostructural materials including nanofibres, nanostrips and hollow nanofibres have been designed and successfully constructed via a uniaxial electrospinning associated with a bi-crucible fluorination technology. Controllable fabrication of unidimensional nanostructural materials is successfully realized via controlling the ingredients and proportions of the spinning solutions and spinning parameters. The influences of roasting temperature, molar proportion of Yb3+ to Er3+ and morphology on the up-converting fluorescence of the samples are studied in detail, and further tunable fluorescence is achieved. Upon the excitation of 980-nm laser, the unidimensional nanostructural materials display excellent up-converting fluorescence. The bright green emissions at 526 and 548 nm are assigned to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 energy levels transition of the Er3+ ions, respectively, and the weaker red characteristic emission peak at 652 nm is attributed to the 4F9/2 → 4I15/2 energy level transition of Er3+. Further, the detailed fluorescent mechanism and the formative mechanism of the unidimensional nanostructural materials are expounded in-depth, and the fabrication techniques are built. Much more importantly, the designing philosophy and fabricating technology can be popularized to manufacture other metal fluoride unidimensional nanostructural materials. The as-synthesized SrF2:Er3+/Yb3+ unidimensional nanostructural materials may find tremendous potential applications in the areas of emitting diodes, displaying devices, optical probes, bioimaging, sensing, drug delivery and lithium-sulfur batteries.

Facile Synthesis of Highly Emissive All-Inorganic Manganese Bromide Compounds with Perovskite-Related Structures for White LEDs

Lead-free all-inorganic halide materials with different Mn2+-based crystal structures (Cs3MnBr5 and CsMnBr3) were obtained using a convenient synthetic method. Cs3MnBr5 had a bright green emission (522 nm), with a unique single-exponential lifetime (τavg = 236 µs) and a high photoluminescence quantum yield (82 ± 5%). A red emission was observed in the case of the CsMnBr3 structure with a two-exponential fluorescence decay curve, and the lifetime was 1.418 µs (93%) and 18.328 µs (7%), respectively. By a judicious tuning of the synthetic conditions, a mixed phase of Cs3MnBr5/CsMnBr3 was also produced that emitted white light, covering almost the entire visible spectrum. White-light-emitting diodes (WLEDs) with color coordinates (0.4269, 0.4955), a color temperature of (3773 K), and a color rendering index (68) were then fabricated using the as-prepared powder of mixed phases of Cs3MnBr5/CsMnBr3 with a commercial UV LED chip (365 nm).

External-Field-Independent Thermometric Sensitivity and Green Emission of Upconversion Phosphor Sr2InF7: Yb3+, Er3.

Based on luminescence intensity ratio (LIR) technology, the noncontact upconversion (UC) optical temperature sensor has aroused a great deal of interest due to its great application prospects in some extreme environments. However, most of the studies focused on improving its sensitivity due to the fact that the sensitivity can be influenced by many external field factors, such as the power density and pulse width of pumping sources or temperature. Herein, a green-emitting UC phosphor Sr2InF7: Yb3+, Er3+ was developed as a potential thermometer, which retained bright green emission under 980 nm excitation with different pulse widths and power densities or at different temperatures; the possible mechanisms are discussed in detail. Its sensitivity almost remained constant when using both continuous wave (c.w.) and pulsed laser or different power densities, which meant the sensitivity of Sr2InF7: Yb3+, Er3+ was independent of the characteristics of pumping laser. A flexible thin-film thermometer composed of Sr2InF7: 2%Yb3+, 2%Er3+ was also fabricated to detect the temperature of microelectronic components, which can not only accurately measure the temperature of the working electronic circuit board but also exhibit excellent repeatability. The results indicated that the present noncontact UC temperature sensor showed stable green emission and thermometric sensitivity as well as the possibility of replacing the traditional thermometers.

Mn2+ doped BaAl11O16N phosphors with narrow band green emission and superior thermal stability for backlighting display applications

Here, BaAl11O16N: Mn2+ green phosphor was synthesized by a two-step high-temperature solid-phase method, and its phase structure, morphology and photoluminescence properties were studied in detail. The phosphor has a wide excitation range of 240–500 nm, and the most effective excitation bands are in the blue spectral regions, indicating that BaAl11O16N: Mn2+ green phosphor can be effectively excited by the commercial blue LED chip. Under the excitation of ultraviolet and blue light, the BaAl11O16N: Mn2+ phosphor shows bright green light emission, with a peak of 514 nm and a half peak width of about 31 nm. The emission properties with temperature change show that the BaAl11O16N: Mn2+ phosphor has good thermal stability and excellent color stability. The white light-emitting diode (a blue InGaN chip combined with BaAl11O16N: 0.25Mn2+ phosphor and a commercial K2SiF6: Mn4+ phosphor) exhibits a NTSC value of 119.3%. Therefore, it can be concluded that the BaAl11O16N: Mn2+ phosphor the ideal choice for wide color gamut backlight as a potential efficient phosphor with green narrow-band emission.

Multicolor upconversion emission and highly optical temperature sensing based on lanthanide-doped double perovskite Sr2LaNbO6 phosphors

Here we adopt trivalent lanthanide (Ln3+ = Er3+, Er3+/Ho3+, and Yb3+/Tm3+) doped Sr2LaNbO6 (SLNO) as novel upconversion luminescence (UCL) materials for achieving UCL and optical temperature sensing under 980 nm excitation. Specifically, Er3+ single doped Sr2LaNbO6 phosphors present bright high-purity green emission under the 980 nm excitation. While co-doping with the Ho3+ ions, the component of red emission from Er3+ ions increases significantly and sample show a remarkable enhancement of luminescent intensity relative to SLNO:Er3+ sample. The above-mentioned phosphors and Yb3+/Tm3+ co-doped phosphor (blue emission) successfully achieve high-purity trichromatic UCL and mixed white light output in the same host. Furthermore, the temperature sensing performance of the SLNO:Er3+/Ho3+ phosphor based on the fluorescence intensity ratio (FIR) is systematically studied for the first time. The temperature sensing based on the non-thermal coupling levels (NTCLs) exhibit higher sensitivity than that based on the thermal coupling levels (TCLs). The maximum absolute and relative sensitivity for 4F9/2/4I9/2 NTCLs reach 0.16803 K−1 at 427 K and 0.01591 K−1 at 641 K, respectively. Interestingly, NIR emission of 4I9/2 → 4I15/2 transition presents a thermal enhancement, while visible emissions show thermal quenching. These results indicate that the Ln3+ doped Sr2LaNbO6 UCL phosphors have potential applications in the fields of non-contact temperature sensors, full-color displays, and anti-counterfeiting.

Moisture-induced phase transition and emission color change for lead-free manganese (II)-Based halide perovskite crystals with greatly improved photoluminescence quantum yield

Halide perovskites with phase transition-sensitive fluorescence color have attracted great attentions in the field of sensing and detection. Though some achievements have been made, the photoluminescence quantum yield (PLQY) for such materials is usually less than 10% before and after phase transition, which is an intrinsic restriction for their application. Herein, we reported a novel lead-free DMAxMnBrx+2 perovskite crystals with moisture-sensitive emission color as well as high PLQY. The result shows that the octahedral coordination of Mn2+ in DMAMnBr3 gives rise to orange emission around 610 nm with PLQY of 41%. While the tetrahedral coordination of Mn2+ in DMA2MnBr4 causes bright green emission nearby 517 nm with a high PLQY of 70%, which is nearly 10 times higher than that of previously reported results. The in situ formation of DMA+ in solution is the key for the dramatically enhanced PLQY. Moreover, as-prepared orange emitted DMAMnBr3 crystals are sensitive to moisture. Just within several tens of second after exposing in the moisture environment, the original orange emission from DMAMnBr3 will turn to green light emission from DMA2MnBr4. The high PLQY of as-prepared DMAxMnBrx+2 perovskite crystals make them possible to be dispersed into non-luminous matrix at a low concentration for moisture detection.

InGaN micro-light-emitting diodes monolithically grown on Si: achieving ultra-stable operation through polarization and strain engineering

Micro or submicron scale light-emitting diodes (µLEDs) have been extensively studied recently as the next-generation display technology. It is desired that µLEDs exhibit high stability and efficiency, submicron pixel size, and potential monolithic integration with Si-based complementary metal-oxide-semiconductor (CMOS) electronics. Achieving such µLEDs, however, has remained a daunting challenge. The polar nature of III-nitrides causes severe wavelength/color instability with varying carrier concentrations in the active region. The etching-induced surface damages and poor material quality of high indium composition InGaN quantum wells (QWs) severely deteriorate the performance of µLEDs, particularly those emitting in the green/red wavelength. Here we report, for the first time, µLEDs grown directly on Si with submicron lateral dimensions. The µLEDs feature ultra-stable, bright green emission with negligible quantum-confined Stark effect (QCSE). Detailed elemental mapping and numerical calculations show that the QCSE is screened by introducing polarization doping in the active region, which consists of InGaN/AlGaN QWs surrounded by an AlGaN/GaN shell with a negative Al composition gradient along the c-axis. In comparison with conventional GaN barriers, AlGaN barriers are shown to effectively compensate for the tensile strain within the active region, which significantly reduces the strain distribution and results in enhanced indium incorporation without compromising the material quality. This study provides new insights and a viable path for the design, fabrication, and integration of high-performance µLEDs on Si for a broad range of applications in on-chip optical communication and emerging augmented reality/mixed reality devices, and so on.

Li+ aided self-activated [formula omitted] phosphors for efficient dual-mode emission and temperature sensing application

For the first time, lanthanide co-doped self-activated Ca9Y1−x−yErxYby(VO4)7 phosphors have been investigated for bearing dual-mode emission: downshifting and upconversion emission behavior. The Ca9Y1−x−yErxYby(VO4)7 phosphor, under 379 nm excitation evinces two bright green emission peaks at 525 nm and 553 nm, which corresponds to H11/22,S3/24→I15/24 transitions of Er3+ ion, this transition is sensitized by an efficient energy transfer from the (VO4)3− group to Er3+ ions. Irradiated with a 980 nm power tunable laser, it shows strong green and comparatively weak red emissions bands. The upconversion emission can be enhanced enormously with the introduction of Li+ ions in the optimized Ca9Y0.847Er0.003Yb0.15(VO4)7 phosphor. Furthermore, utilizing the well-known fluorescence intensity ratio (FIR) technique, optimized Ca9Y0.647Li0.20Er0.003Yb0.15(VO4)7 phosphor has been explored for optical temperature sensors also. The maximum absolute sensitivity and relative sensitivity are obtained to be 0.0125 K−1 at 513 K and 0.012 K−1 at 300 K, respectively. The acquired result reveals that the phosphor Ca9Y0.647Li0.20Er0.003Yb0.15(VO4)7 can be a worthy material for temperature sensing application.

Highly luminescent and stable lanthanide coordination polymers based 2-(3′,4′-dicarboxyphenoxy)-benzoic acid: Crystal structure, photoluminescence, white light emission and fluorescence sensing

New lanthanide coordination polymers (Ln-CPs), {[Ln(DPBA)(phen)2]·2H2O}n (Ln = Eu 1, Tb 2, Gd 3), based on a ternary system containing 2-(3′,4′-dicarboxyphenoxy)-benzoic acid (H3DPBA) and 1,10-phenanthroline (phen) were hydrothermally prepared. The Ln-CPs exhibit a 1D structure with [LnO4N4] polyhedra and DPBA ligands, which can be extended to a 3D supramolecular network by water clusters and π-stacking. The coordination polymers have remarkable thermal stability up to 340 °C and solvent stability (in various solvents containing water in the 3–12 pH range). 1, 2, 3 show bright red, green, and blue emissions, respectively. Notably, 1 exhibits a very high photoluminescence quantum yield (PLQY) of 86%, which is among the best values for Ln-CPs. Energy transfer analysis is performed for Ln-CPs by DFT/TD-DFT calculations, solid-state phosphorescence (77 K) and UV–vis absorption spectra of Gd-CP. Favorable photostability of 1 is observed through a UV aging experiment, which shows that the PLQY of 1 maintained 55% of its initial value after 150 h Ultraviolet A (UVA) irradiation, which makes it potentially useful as a light conversion material. In addition, the Gd0.993Eu0.0017Tb0.0053-CP codoped system shows white emission with a high PLQY of 35.09%, which is among the highly ranked as compared with reported white light emissions based on Ln-CPs. This highly luminescent Eu-CP can also be used as a sensitive fluorescence sensor for antibiotic detection in aqueous solution.

2D polymeric lanthanide(III) compounds based on novel bright green emitting enaminone ligand

New enaminone derivative, 2-{[(4-methoxyphenyl)amino]methylene}-5,5-dimethyl-cyclohexane-1,3-dione (HL), and lanthanide(III) compounds based on it [Ln(HL)2(NO3)3]n, (where Ln3+=Eu (1Eu), Sm (2Sm), Tb(3 Tb) and Dy (4Dy)) have been synthesized. The complexes have been fully characterized by spectroscopic and analytical methods including single crystal X-ray structure. To establish closer intermolecular contacts and HOMO/LUMO energy, the Hirshfeld surface analysis, as well as DFT calculations has been carried out. According to single-crystal X-ray diffraction analysis ligand exhibits bidentate-bridging mode. This leads to the formation of polymeric structure as layer, arranged parallel to ab crystallographic plane. The lanthanide polyhedron is close to bicapped square antiprism. All obtained compounds are isomorphous to each other. The study of photoluminescence showed the presence of a bright green emission of the ligand with a quantum yield of 41 %. The weak sensitization occurs only in case of europium(III) complex leading to apparent luminescence quantum yield of 0.021 %, with ∼4 % sensitization efficiency. Emission spectra of other compounds are the same to the ligand one.

Mechanochemistry-driven engineering of 0D/3D heterostructure for designing highly luminescent Cs–Pb–Br perovskites

Embedding metal-halide perovskite particles within an insulating host matrix has proven to be an effective strategy for revealing the outstanding luminescence properties of perovskites as an emerging class of light emitters. Particularly, unexpected bright green emission observed in a nominally pure zero-dimensional cesium–lead–bromide perovskite (Cs4PbBr6) has triggered intensive research in better understanding the serendipitous incorporation of emissive guest species within the Cs4PbBr6 host. However, a limited controllability over such heterostructural configurations in conventional solution-based synthesis methods has limited the degree of freedom in designing synthesis routes for accessing different structural and compositional configurations of these host–guest species. In this study, we provide means of enhancing the luminescence properties in the nominal Cs4PbBr6 powder through a guided heterostructural configuration engineering enabled by solid-state mechanochemical synthesis. Realized by an in-depth study on time-dependent evaluation of optical and structural properties during the synthesis of Cs4PbBr6, our target-designed synthesis protocol to promote the endotaxial formation of Cs4PbBr6/CsPbBr3 heterostructures provides key insights for understanding and designing kinetics-guided syntheses of highly luminescent perovskite emitters for light-emitting applications.

Photoluminescence of Bi3+ in LiCaY5(BO3)6 and color-tunable emission through energy transfer to Eu3+/Tb3+

Bi3+ has an outer shell lone pair electrons and the energy of 6p orbitals are also sensible to the coordination environment, therefore its typical wide band excitation and emission spectra are highly dependent on the host structure. The recently reported LiCaY5(BO3)6 has multiple sites suitable for cationic doping. In this work, Bi3+ singly doped phosphors and Bi3+/Eu3+ and Bi3+/Tb3+ co-doped phosphors were prepared by high temperature solid state reactions. Careful Rietveld refinements on powder X-ray diffraction suggest the site-preferential doping of Bi3+ into M3 site, which has an octahedral cavity. By 1 atom% doping, Bi3+ exhibits a broad emission band centered at 364 nm with an internal quantum efficiency of 39.8%. The energy transfer to Eu3+/Tb3+ are firmly proved by both the emission intensity change and the decay curves, which is likely through the dipole-dipole interactions. Color-tunable emissions from blue to red, or from blue to green have been realized and the combination with 275 nm LED chip gives the bright blue, red and green emission for LiCa(Y0.99Bi0.01)5(BO3)6, LiCa(Y0.69Bi0.01Eu0.3)5(BO3)6, and LiCa(Y0.69Bi0.01Tb0.3)5(BO3)6, respectively.

Structural and temperature-dependent luminescence of Terbium doped YAl3(BO3)4 phosphor synthesized by the combustion method

A series of Y1-xAl3(BO3)4:x Tb3+ (x = 0.5 to 7 wt%) phosphors synthesized by a gel combustion method have been systemically investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDS), and photoluminescence (PL) as a function of temperature from 300 K to 10 K and 300 K–550 K. An XRD analysis confirms that the phosphors crystallized, and its crystal structure was analysed. The synthesized phosphor matches the XRD pattern provided in the ICSD File No 96-152-6006. The FTIR analysis indicates that nitrates and organic matter have been completely removed and the BO3 groups are present. The broad PL band peaked at 420 nm with a shoulder circa 460 nm of YAl3(BO3)4 is associated with hydrous components which attached to the sample in environmental conditions after synthesis. The PL spectra of YAl3(BO3):Tb3+ phosphors exhibit a bright and narrow green main emission peak at 543 nm corresponding to the 5D4 →7F5 transition under 359 nm excitation. The PL intensity increases with increasing Tb3+ ion concentration up to 5 wt %, followed by evidence for concentration quenching. There is a possibility that higher concentration quenching could be from confinement effects of localised resonant energy transfer. PL data revealed that activation energies for thermal quenching at 485 nm and 543 nm were found to be 0.659 and 0.092 eV, and 0.585 and 0.087 eV, respectively.