Microwave-assisted synthesis of GdOF: Eu3+/Tb3+ ultrafine phosphor powders suitable for advanced forensic and security ink applications

The rare-earth-doped inorganic ultrafine oxyfluoride host matrices in forensic science, especially in latent fingerprint detection and anti-counterfeiting applications, were still unexplored and may replace the existing technology owing to its high sensitivity. Herein, GdOF: Eu³⁺/Tb³⁺ ultrafine red and green phosphors were synthesized via a rapid, green microwave-assisted hydrothermal method at 150 °C. The phosphors synthesized by this novel method possess good luminescent intensity for the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ and ⁵D₄→⁷F₅ transition of Tb³⁺ ions as compared to the phosphors prepared via other conventional methods such as co-precipitation synthesis, sol-gel synthesis, and microwave-assisted co-precipitation synthesis. Further, an enhancement in the luminescent intensity of the ultrafine phosphor was noticed when the microwave parameters and pH values were tuned. The optimized red and green phosphors having high luminescence intensity, good color purity, and high quantum yields of 89.3%, and 71.2%, respectively, were used for the visualization of latent fingerprints on various substrates. These promising phosphors exhibited excellent visualization regardless of the background interference and limit the risk of duplication and are highly reliable. The security inks developed using these phosphors are highly efficient for anti-counterfeiting applications. These multifunctional properties of investigated phosphors can be explored for security applications.

Systematic Study on the Luminescent Properties, Thermal Stability, and Magnetic Behavior of GdOF: RE3+ (RE = Eu, Yb, and Er) Red Phosphors with Various Morphologies

In this work, GdOF:RE³⁺ (RE = Eu, Yb, and Er) phosphors with high thermally stable luminescence were reported, which were synthesized by an ionic liquid-assisted two-phase system and subsequent calcination technique for the first time. Nanodisks, nanorod aggregates, nanoneedles, and stubby nanorods were obtained by simply regulating the pH value. The luminescent properties of precursors and products were discussed in detail. By carefully adjusting the calcination temperature and the pH value of the initial system, pure red emission was achieved in both GdOF:Eu³⁺ and GdOF:Yb³⁺, Er³⁺ phosphors. The reason for distinct luminescent properties of different products was discussed from various perspectives. Moreover, the temperature-dependent spectra were measured and the GdOF:Eu³⁺ and GdOF:Yb³⁺, Er³⁺ products both exhibited outstanding thermal stability. In addition, the as-prepared nanomaterials presented paramagnetic properties, indicating their potential application in both field-emission displays and magnetic resonance imaging technology.

Photoluminescence and structural analysis of trivalent europium doped MLaAl3 O7 (M = Ba, Ca, Mg and Sr) nanophosphors

The solution combustion technique was used to synthesize MLaAl₃ O₇ (M = Ba, Ca, Mg, and Sr) nanophosphors-doped with Eu³⁺ using metal nitrates as precursors. The photoluminescence (PL) emission spectra exhibited three peaks at 587-591, 610-616, and 653-654 corresponding to ⁵ D₀ →⁷ F₁ , ⁵ D₀ →⁷ F₂ , and ⁵ D₀ →⁷ F₃ transitions, respectively. Upon excitation at 254 nm, these nanophosphors displayed strong red emission with the dominant peak attributed to the ⁵ D₀ →⁷ F₂ transition of Eu³⁺ . The materials were further heated at 900 and 1050°C for 2 h to examine the consequence of temperature on crystal lattice and PL emission intensity. X-ray diffraction (XRD) analysis proved that all the synthesized materials were of a crystalline nature. CaLaAl₃ O₇ material has a tetragonal crystal structure with space group P421m. Scherer's equation was used to calculate the crystallite size of synthesized phosphors using XRD data. A Fourier transformation infrared study was used to observe the stretching vibrations of metal-oxygen bonds. Infrared peaks for stretching vibrations corresponding to lanthanum-oxygen and aluminium-oxygen bonds were found at 582 and 777 cm^-1 respectively for CaLaAl₃ O₇ phosphor material. Transmission electron microscopy images were used to determine the size of particles (18-37 nm for the as-prepared materials) and also to analyze the three-dimensional view of these materials. The experimental data indicate that these materials may be promising red-emitting nanophosphors for use in white light-emitting diodes.

Optical and x-ray technology synergies enabling diagnostic and therapeutic applications in medicine

X-ray and optical technologies are the two central pillars for human imaging and therapy. The strengths of x-rays are deep tissue penetration, effective cytotoxicity, and the ability to image with robust projection and computed-tomography methods. The major limitations of x-ray use are the lack of molecular specificity and the carcinogenic risk. In comparison, optical interactions with tissue are strongly scatter dominated, leading to limited tissue penetration, making imaging and therapy largely restricted to superficial or endoscopically directed tissues. However, optical photon energies are comparable with molecular energy levels, thereby providing the strength of intrinsic molecular specificity. Additionally, optical technologies are highly advanced and diversified, being ubiquitously used throughout medicine as the single largest technology sector. Both have dominant spatial localization value, achieved with optical surface scanning or x-ray internal visualization, where one often is used with the other. Therapeutic delivery can also be enhanced by their synergy, where radio-optical and optical-radio interactions can inform about dose or amplify the clinical therapeutic value. An emerging trend is the integration of nanoparticles to serve as molecular intermediates or energy transducers for imaging and therapy, requiring careful design for the interaction either by scintillation or Cherenkov light, and the nanoscale design is impacted by the choices of optical interaction mechanism. The enhancement of optical molecular sensing or sensitization of tissue using x-rays as the energy source is an important emerging field combining x-ray tissue penetration in radiation oncology with the molecular specificity and packaging of optical probes or molecular localization. The ways in which x-rays can enable optical procedures, or optics can enable x-ray procedures, provide a range of new opportunities in both diagnostic and therapeutic medicine. Taken together, these two technologies form the basis for the vast majority of diagnostics and therapeutics in use in clinical medicine.

A novel color-tunable phosphor, Na5Gd9F32:Ln3+ (Ln = Eu, Tb, Dy, Sm, Ho) sub-microcrystals: structure, luminescence and energy transfer properties

Ln3+-Doped fluorides are economical and highly efficient luminescent materials, which play a crucial role in LEDs, biolabeling, and sensors. Therefore, Na5Gd9F32:Ln3+ sub-microspheres with tunable multicolor emissions were successfully synthesized via a simple water bath method employing colloidal Gd(OH)CO3 spheres as precursors. Samples were characterized by XRD, SEM, TEM, EDS and PL. It was found that the hydrolysis of BF4- ions had a dynamic effect on the retention of the morphology of the product owing to the mild reaction environment caused by the low hydrolysis rate of BF4- ions. Upon excitation by ultraviolet light, the Na5Gd9F32:Ln3+ (Ln = Eu, Tb, Dy, Sm, Ho) phosphors underwent characteristic f-f transitions and gave rise to red, green, green, yellow, and pale green emissions, respectively. Moreover, various emission colors could be obtained by using different excitation wavelengths and adjusting the Eu3+/Tb3+ molar ratio owing to energy transfer between Tb3+ and Eu3+ ions in the Na5Gd9F32 host. The energy transfer mechanism was demonstrated to be a dipole-dipole interaction. The multicolor luminescent phosphors with a certain dopant concentration based on a single host and excitation wavelength may have potential applications in the field of lighting displays.

Silica-modified luminescent LaPO4 :Eu@LaPO4 @SiO2 core/shell nanorods: Synthesis, structural and luminescent properties

Monoclinic-type tetragonal LaPO₄ :Eu (core) and LaPO₄ :Eu@LaPO₄ (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano-products were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO₄ and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications.

A facile route to the controlled synthesis of β-NaLuF4:Ln3+ (Ln = Eu, Tb, Dy, Sm, Tm, Ho) phosphors and their tunable luminescence properties

Highly uniform and monodisperse β-NaLuF₄:Ln³⁺ (Ln = Eu, Tb, Dy, Sm, Tm, Ho) hexagonal prisms have been synthesized via a facile two-step hydrothermal method without any organic surfactants.

Morphology control and photoluminescence properties of Eu3+-activated Y4Al2O9 nanophosphors for solid state lighting applications

Spherical Eu³⁺:Y₄Al₂O₉ nanophosphors exhibit brilliant PL behavior with enhanced color purity and excited state lifetime.

Dy3+ -, Sm3+ -, Ce3+ - and Tb3+ -activated optical properties of microcrystalline BaMgP2 O7 phosphors

Photoluminescence (PL) and thermoluminescence (TL) properties of rare earth (RE) ion (RE = Dy³⁺ , Sm³⁺ , Ce³⁺ , Tb³⁺ ) activated microcrystalline BaMgP₂ O₇ phosphors are presented in this work. Non-doped and doped samples of BaMgP₂ O₇ were prepared using a solid state diffusion method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), PL and TL. The XRD measurement confirmed the phase purity of the BaMgP₂ O₇ host matrix. The average particle size was found through SEM measurement to be around 2 μm. All activators using the PL technique displayed characteristic excitation and emission spectra that corresponded to their typical f → f and f → d transitions respectively. Thermoluminescence measurements showed that BaMgP₂ O₇ :RE (RE = Dy³⁺ , Sm³⁺ , Tb³⁺ , Ce³⁺ ) and co-doped BaMgP₂ O₇ :Ce³⁺ ,Tb³⁺ phosphors have also TL behaviour.

Controllable Synthesis of Monodisperse Er3+-Doped Lanthanide Oxyfluorides Nanocrystals with Intense Mid-Infrared Emission

Monodisperse lanthanide oxyfluorides LnOF (Ln = Gd, Y) with mid-infrared emissions were controllably synthesized via a mild co-precipitation route and a subsequent heat-treatment. The detailed composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM). The results showed that monodisperse GdOF:Er³⁺ were nano-riced shape with length about 350 nm and width about 120 nm, while the quasi-spherical YOF:Er³⁺ were uniform nanocrystals with an average size around 100 nm. The influence of calcination temperature on the size and phase transition of LnOF nanocrystals was also investigated. The photoluminescence (PL) spectra indicated that the 2.7 μm emission of Er³⁺ had achieved in both GdOF and YOF nanocrystals, which were calcined at different temperatures. In addition, the decay time of both ⁴I_13/2 and ⁴I_13/2 energy levels corresponding to Er³⁺ in YOF nanocrystals were also studied in detail. The results suggested that both rice-shaped GdOF nanocrystals and YOF nanocrystals could provide suitable candidate materials for nanocrystals-glass composites, which could be a step forward to the realization of mid-infrared laser materials.

Luminescence analysis of SrGa2 Si2 O8 : RE3+ (RE = Dy, Tm) phosphors

This article reports on the luminescence properties of rare earth (Dy³⁺ and Tm³⁺ )ions doped SrGa₂ Si₂ O₈ phosphor were studied. SrGa₂ Si₂ O₈ phosphors weresynthesizedby employing solid state reaction method.From the measured X-ray diffraction (XRD) pattern of the samplemonoclinic phase structure has been observed. Thermoluminescenceand Mechanoluminescence properties of the γ-ray irradiated samples have been studied. Photoluminescence spectra of Dy³⁺ activated SrGa₂ Si₂ O₈ phosphor has been measured with an excitation wavelength at 348 nm,and it shows two emission bands at 483 and 574 nm due to ⁴ F_9/2  → ⁶ H_15/2 and ⁴ F_9/2  → ⁶ H_13/2 transitions respectively. Whereas the photoluminescence spectra of Tm³⁺ activated SrGa₂ Si₂ O₈ phosphor has been measured with an excitation wavelength at 359 nm and it exhibits two emission bands at 454 and 472 nm due to ¹ D₂  → ³ F₄ and¹ G₄  → ³ H₆ transitions respectively. In thermoluminescence study, γ-irradiatedthermoluminescence glow curve of SrGa₂ Si₂ O₈ :Dy³⁺ phosphor shows two well defined peaks at 293 °C (peak1)and 170 °C (peak2) whereas thermoluminescence glow curve of SrGa₂ Si₂ O₈ :Tm³⁺ phosphor shows peaks at 292 °C (peak1) and 184 °C (peak2) indicating that two sets of traps are being activated within the particular temperature range and the trapping parameters associated with the prominent glow peaks of SrGa₂ Si₂ O₈ :Dy³⁺ and SrGa₂ Si₂ O₈ :Tm³⁺ are calculated using Chen's peak shape and initial rise method.From the Mechanoluminescence study, only one glow peak has been observed. Copyright © 2016 John Wiley & Sons, Ltd.

Rapid, morphology-controllable synthesis of GdOF:Ln3+ (Ln = Eu, Tb) crystals with multicolor-tunable luminescence properties

This work investigates a facile and mass-production method to synthesize multiform morphologies of GdOF and obtains multicolor emissions in GdOF:Tb³⁺,Eu³⁺ samples.

Energy transfer and tunable multicolor emission and paramagnetic properties of GdF3:Dy3+,Tb3+,Eu3+ phosphors

GdF₃:RE³⁺ (RE = Dy³⁺, Tb³⁺, Eu³⁺) phosphors can realize multicolor emission including white light. Simultaneously, GdF₃:RE³⁺ (RE = Dy³⁺, Tb³⁺, Eu³⁺) phosphors also exhibit paramagnetic properties at room temperature and low temperatures.

BaGdF5:Dy3+,Tb3+,Eu3+ multifunctional nanospheres: paramagnetic, luminescence, energy transfer, and tunable color

The photoluminescence emission color tones of BaGdF₅:Dy³⁺,Tb³⁺,Eu³⁺ nanomaterials change from yellow-green to red by adjusting the doping concentration and the different excitation wavelengths. Furthermore, the obtained samples also exhibit paramagnetic properties.

White light-emitting, tunable color luminescence, energy transfer and paramagnetic properties of terbium and samarium doped BaGdF5 multifunctional nanomaterials

Multicolor luminescence of BaGdF₅:Tb³⁺,Sm³⁺ nanospheres can be obtained by adjusting the excitation wavelength. The obtained phosphors also exhibit paramagnetic properties at room temperature and low temperature.

Host-sensitized luminescence in LaNbO4:Ln(3+) (Ln(3+) = Eu(3+)/Tb(3+)/Dy(3+)) with different emission colors

In this work, a series of Eu(3+), Tb(3+), and Dy(3+) singly-doped and co-doped LaNbO4 (LNO) phosphors have been synthesized by a high-temperature solid-state reaction route. X-ray diffraction (XRD) along with Rietveld refinement, diffuse reflection spectra, photoluminescence (PL) and cathodoluminescence (CL) properties, decay lifetimes, and PL quantum yields (QYs) were exploited to characterize the phosphors. Under UV excitation, energy transfer process from the host to the activators exists in the singly-doped samples, which leads to tunable emission color from blue to red for LNO:Eu(3+), green for LNO:Tb(3+), and yellow including white for LNO:Dy(3+). In Eu(3+) and Tb(3+) co-doped phosphors, LNO:Eu(3+), Tb(3+), the energy transfers from the host to the activators and Tb(3+) to Eu(3+) ions have also been deduced from the PL spectra, resulting in tunable emission color from green to red by adjusting the concentration ratio of Eu(3+) and Tb(3+) ions. The decay times monitored at host emission and Tb(3+) emission confirm the existence of energy transfer in the as-prepared samples. The best quantum efficiency can reach 43.2% for LNO:0.01Tb(3+) among all the as-prepared phosphors. In addition, the CL spectra of LNO:Eu(3+)/Tb(3+)/Dy(3+) are a little different from their PL spectra because another emission envelope around 530 nm appears in the samples, which is attributed to the bombardment of higher energy excitation source of low-voltage electron beam. However, the characteristic emissions similar to PL spectra were reserved. Moreover, the CL spectrum of LNO:0.02Tb(3+) has stronger emission intensity than that of ZnO:Zn commercial product. These results from the PL and CL properties of LNO:Eu(3+)/Tb(3+)/Dy(3+) suggest their potential in solid-state lighting and display fields.

Recent progress in low-voltage cathodoluminescent materials: synthesis, improvement and emission properties

Nowadays there are several technologies used for flat panel displays (FPDs) and the development of FPDs with enhanced energy efficiency and improved display quality is strongly required. Field emission displays (FEDs) have been considered as one of the most promising next generation flat panel display technologies due to their excellent display performance and low energy consumption. For the development of FEDs, phosphors are irreplaceable components. In the past decade, the study of highly efficient low-voltage cathodoluminescent materials, namely FED phosphors, has become the focus of enhancing energy efficiency and realizing high-quality displays. This review summaries the recent progress in the chemical synthesis and improvement of novel, rare-earth and transition metal ions activated inorganic cathodoluminescent materials in powder and thin film forms. The discussion is focused on the modification of morphology, size, surface, composition and conductivity of phosphors and the corresponding effects on their cathodoluminescent properties. Special emphases are given to the selection of host and luminescent centers, the adjustment of emission colors through doping concentration optimization, energy transfer and mono- or co-doping activator ions, the improvement of chromaticity, color stability and color gamut as well as the saturation behavior and the degradation behavior of phosphors under the excitation of a low-voltage electron beam. Finally, the research prospects and future directions of FED phosphors are discussed with recommendations to facilitate the further study of new and highly efficient low-voltage cathodoluminescent materials.

Crystal-site engineering control for the reduction of Eu(3+) to Eu(2+) in CaYAlO4: structure refinement and tunable emission properties

In this article, Eu-activated CaYAlO4 aluminate phosphors were synthesized by a solid-state reaction. Under UV light excitation, characteristic red line emission of Eu(3+) was detected in the range of 570-650 nm. In addition, we introduced crystal-site engineering approach into the CaYAlO4 host through incorporation of Si(4+)-Ca(2+) to replace Al(3+)-Y(3+), which would shrink the AlO6 octahedrons, accompanied by the expansion of CaO9 polyhedron, and then enable the partial reduction of Eu(3+) to Eu(2+). The crystal structure and underlying mechanism have been clarified on the basis of the Rietveld refinement analysis. The PL spectra of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) exhibit both green emission of Eu(2+) (4f(6)5d(1)-4f(7), broadband around 503 nm) and red-orange emission of Eu(3+) ((5)D0-(7)F1,2, 593 and 624 nm) under UV light excitation with a quantum yield of 38.5%. The CIE coordinates of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) phosphors are regularly shifted from (0.482, 0.341) to (0.223, 0.457) with increasing x, which would expand the application of Eu. Furthermore, this investigation reveals the correlations of structure and property of luminescent materials, which would shed light on the development of novel phosphors suitable for lighting and display applications.

Morphology control and multicolor-tunable luminescence of YOF:Ln3+ (Ln = Eu, Tb, Dy, Tm) nano-/microcrystals

Multiform YOF nano-/microcrystals have been synthesized and multicolor-tunable luminescence of YOF:Ln³⁺ (Ln = Eu, Tb, Dy, Tm, Tm/Dy) has been investigated.

Cubic KLu3F10 nanocrystals: Mn2+ dopant-controlled synthesis and upconversion luminescence

Rare-earth-doped cubic KLu₃F₁₀ nanocrystals with excellent upconversion luminescence have been fabricated by adding Mn²⁺ ions.

Tunable luminescence properties of the novel Tm3+- and Dy3+-codoped LiLa(MoO4)x(WO4)2−x phosphors for white light-emitting diodes

Tm³⁺ can transfer energy to Dy³⁺ efficiently, and with increase in MoO₄²⁻ content, the chromaticity coordinates changed from the edge to the center of the white area.

Monodisperse lanthanide oxyfluorides LnOF (Ln = Y, La, Pr-Tm): morphology controlled synthesis, up-conversion luminescence and in vitro cell imaging

Lanthanide oxyfluorides LnOF (Ln = Y, La, Pr-Tm) nano/micro-materials with a variety of well-defined morphologies including nanorods, nanospindles, nanorod-bundles and nanospheres, have been successfully synthesized via a facile precipitation technique followed by a heating treatment. It is found that the pH values, fluoride sources and dosage of urea in the initial reaction systems play critical roles in the morphology determination of the LnOF products and the possible formation mechanism for these diverse architectures has been presented. XRD, FT-IR, TG-DTA, SEM, TEM, as well as up-conversion (UC) luminescence spectra are used to characterize the synthesized samples. Under 980 nm NIR laser excitation, red, green and blue UC luminescence are observed from Yb(3+)/Er(3+), Yb(3+)/Ho(3+) and Yb(3+)/Tm(3+) co-doped YOF nanospheres. The MTT assay indicates that YOF nanospheres exhibit good biocompatibility. Especially, the emission spectrum of YOF: 0.20Yb(3+), 0.04Er(3+) nanospheres is dominated by a single red emission at 660 nm, which falls into the "optical window" of biological tissues. The application of YOF: 0.20Yb(3+), 0.04Er(3+) nanospheres in the cell imaging is also investigated, which shows a bright-red emission without background noise.

YOF nano/micro-crystals: morphology controlled hydrothermal synthesis and luminescence properties

SEM images and multicolored down-conversion and up-conversion luminescence photographs of the YOF: Ln³⁺ nano/micro-structures.