Phase-dependent Photoluminescence Research Articles

Spherical red-emitting X1-Y2SiO5:Eu and α-Y2Si2O7:Eu phosphors with high color purity: The evolution of morphology, phase and photoluminescence upon annealing

Spherical silicate phosphor has widespread application in display or lighting industry. By using spherical silica particles as the core, we successfully prepared shell-thickness-controllable core/shell spherical particles, which can then be controllably converted to spherical X1-Y2SiO5:Eu (YSO:Eu) and α-Y2Si2O7:Eu (YPS:Eu) particles upon annealing. Even after 1000–1200 °C annealing, both X1-YSO:Eu and α-YPS:Eu particles still had the spherical shape and narrow size distribution. The shell thickness and annealing temperature synergistically controlled the phase evolution upon annealing. Thinner shell of around 30 nm, having extremely high chemical reaction activity, promoted the formation of spherical X1-YSO:Eu particles at 1000 °C and α-YPS:Eu particles at 1100 °C. Shell of around 85 nm produced spherical X1-YSO:Eu particles at 1100 °C and α-YPS:Eu particles at 1200 °C. Thicker shell also promoted the formation of spherical particles, but these particles usually had the mixed silicate phases. The phase-dependent photoluminescence properties were investigated in detail. Both spherical X1-YSO:Eu and α-YPS:Eu phosphors emitted reddish-orange color, with nearly 100% color purity and dominant wavelength of around 601 nm, which would absorb great attention for the application in display or lighting devices.

Bright Luminescence in Three Phases-A Combined Synthetic, Spectroscopic and Theoretical Approach.

Combining phase‐dependent photoluminescence (PL) measurements and quantum chemical calculations is a powerful approach to help understand the influence of the molecular surroundings on the PL properties. Herein, a phosphine functionalized amidinate was used to synthesize a recently presented bimetallic gold complex, featuring an unusual charge separation. The latter was subsequently used as metalloligand to yield heterotetrametallic complexes with an Au‐M‐M‐Au “molecular wire” arrangement (M=Cu, Ag, Au) featuring metallophilic interactions. All compounds show bright phosphorescence in the solid state, also at ambient temperature. The effect of the molecular environment on the PL was studied in detail for these tetrametallic complexes by comparative measurements in solution, in the solid state and in the gas phase and contrasted to time‐dependent density functional theory computations.

Bright Luminescence in Three Phases—A Combined Synthetic, Spectroscopic and Theoretical Approach

AbstractCombining phase‐dependent photoluminescence (PL) measurements and quantum chemical calculations is a powerful approach to help understand the influence of the molecular surroundings on the PL properties. Herein, a phosphine functionalized amidinate was used to synthesize a recently presented bimetallic gold complex, featuring an unusual charge separation. The latter was subsequently used as metalloligand to yield heterotetrametallic complexes with an Au‐M‐M‐Au “molecular wire” arrangement (M=Cu, Ag, Au) featuring metallophilic interactions. All compounds show bright phosphorescence in the solid state, also at ambient temperature. The effect of the molecular environment on the PL was studied in detail for these tetrametallic complexes by comparative measurements in solution, in the solid state and in the gas phase and contrasted to time‐dependent density functional theory computations.

A phase-dependent photoluminescent discotic liquid crystal bearing a graphdiyne substructure.

In recent years, graphdiyne and its derivatives with fascinating electro-optic properties have attracted tremendous scientific attention. Here we design and synthesize a graphdiyne-derived discotic liquid crystal material by decorating six wedge-shaped 3,4,5-tris(dodecyloxy)benzoate groups on the fundamental structural unit of graphdiyne, the dehydrotribenzo[18]annulene core. This graphdiyne-derived liquid crystal material exhibits a cubic phase and a hexagonal columnar phase at varied temperatures. Most interestingly, this molecule displays a tunable phase-dependent photoluminescence behavior. Under the irradiation of 365 nm wavelength ultraviolet light, the luminescent material emits pale blue, green and azure light in the cubic, hexagonal columnar and isotropic phases respectively. This graphdiyne-derived discotic liquid crystal with excellent optical characteristics might have application potentials in organic optoelectronic functional materials and devices.

Phase dependent photoluminescence and thermoluminescence properties of Y2SiO5:Sm3+ nanophosphors and its advanced forensic applications

In the present work, a series of Sm3+ doped Y2SiO5 orange red nanophosphor were synthesized via ultrasonication route. The structural, morphology and luminescent properties of X1 and X2 phased products were thoroughly investigated. SEM images exhibit irregular shaped particles. The optimum doping concentration was found to be 3 mol % for Sm3+ ion and the critical distance Rc was estimated to be ~9.47 Å. The dipole-dipole interaction was main liable for concentration quenching. The photometric properties of the prepared nanophosphors were estimated, which indicates that the nanophosphor may be potentially excited NUV chips for application in W-LEDs. The Judd-Ofelt intensity parameters and radiative parameters were estimated. In order to investigate their thermoluminescence properties, prepared products were irradiated to γ -dose in the range from 1 to 5 kGy. Characteristic TL glow curves of X1 phase consists of peaks at 398, 468, 554 and 599 K. However, in X2 phase peaks at 471, 521, 575 and 619 K were recorded. The dose-response plots were linear. The kinetic parameters were estimated by various methods and compared. The optimized Y2SiO5:Sm3+ (3 mol %) nanophosphor was employed to visualize latent fingerprints with high sensitivity, low backward hindrance and simple setup using optimized sample under UV 254 nm light. The aforesaid outcomes signify the fabricated nanophosphor display outstanding luminescence properties leads to significant applications, such as WLED's, dosimetry and forensic science.

Phase-dependent photoluminescence behavior of Cr-doped alumina phosphors

Cr-doped amorphous, γ, θ and α-alumina phosphors are carefully synthesized and comprehensively studied to reveal correlations between crystal structure, doping concentration and photoluminescence property. All phosphors exhibit characteristic phase dependent emission behavior: their luminescence intensity and peak position are found to be closely dependent on crystal structure of alumina phases. Luminescence intensity and critical quenching concentration increase drastically with phase transition sequence of amorphous–γ–θ–α. Crystal field parameters are extracted from UV–Vis spectra and the calculated Dq/B values of all alumina phases are larger than 2.3. An alternative possible emission mechanism for γ and θ alumina is deduced from the emission character.

Engineering Parallel and Perpendicular Polarized Photoluminescence from a Single Semiconductor Nanowire by Crystal Phase Control

We report on a crystal phase-dependent photoluminescence (PL) polarization effect in individual wurtzite GaAs nanowires with a zinc blende GaAsSb insert grown by Au-assisted molecular beam epitaxy. The PL emission from the zinc blende GaAsSb insert is strongly polarized along the nanowire axis while the emission from the wurtzite GaAs nanowire is perpendicularly polarized. The results indicate that the crystal phases, through optical selection rules, are playing an important role in the alignment of the PL polarization in nanowires besides the linear polarization induced by the dielectric mismatch. The strong excitation power dependence and long recombination lifetimes ( approximately 4 ns) from the wurtzite GaAs and zinc blende GaAsSb-related PL emission strongly indicate the existence of type II band alignments in the nanowire due to the presence of nanometer thin zinc blende segments and stacking faults in the wurtzite GaAs barrier.

Self-templated and self-assembled synthesis of nano/microstructures of Gd-based rare-earth compounds: morphology control, magnetic and luminescence properties

Nearly monodisperse NaGdF(4) and GdF(3) nanowires/nanorods as well as GdBO(3) microplates/microflowers have been successfully prepared by a designed chemical conversion approach using Gd(OH)(3) nanowires/nanorods as precursors via a facile hydrothermal approach. The Gd(OH)(3) nanowires/nanorods precursors were prepared through a simple hydrothermal process, which then served as sacrificial templates for the fabrication of NaGdF(4) and GdF(3) nanowires/nanorods as well as GdBO(3) microplates/microflowers by a hydrothermal process. The possible formation mechanisms for the corresponding Gd(3+)-based various products are presented in detail. We have investigated the magnetic properties of the NaGdF(4), GdF(3), and GdBO(3) samples. The as-obtained Eu(3+) doped NaGdF(4), GdF(3), and GdBO(3) samples show the strong characteristic red emission of Eu(3+) under ultraviolet excitation. Moreover, the luminescence colors of the Eu(3+) and Tb(3+) co-doped GdBO(3) samples can be tuned from red, through orange, yellow and green-yellow, to green by simply adjusting the relative doping concentrations of the activator ions under a single wavelength excitation, which might find potential applications in the fields such as light display systems and optoelectronic devices. More importantly, this simple method is expected to allow the large-scale production of other complex rare-earth compounds with controllable morphologies and sizes, and exploration of the morphology and phase-dependent photoluminescence properties.

Amino Acid-Assisted Synthesis of ZnO Hierarchical Architectures and Their Novel Photocatalytic Activities

A facile and bioinspired synthesis of ZnO hierarchical architectures, including prismlike and flowerlike structures and crytalline and noncrystalline hollow microspheres, has been developed using the amino acid histidine as the directing and assembling agent. The histidine molecules play different roles in the formation of ZnO hierarchical architectures due to the competitive coordination between histidine and OH− to Zn2+ when the reactant molar ratios are adjusted. The resulting architectures are characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectoscopy, and thermogravimetric analysis (TGA). Morphology- and phase-dependent photoluminescence of the ZnO architectures has been shown. In particularly, a novel photocatalytic activity of the ZnO hierarchical architectures for the reaction of the formaldehyde and carbon dioxide has been demonstrated, prob...

Shape controllable synthesis and upconversion properties of NaYbF4/NaYbF4:Er3+ and YbF3/YbF3:Er3+ microstructures

Ytterbium fluoride compounds with different crystal phases and morphologies, such as β-NaYbF4 hexagonal microdisks, microprisms, microtubes, and α-NaYbF4 submicrospheres as well as YbF3 octahedra, have been synthesized via a facile hydrothermal route. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL) spectra were used to characterize the samples. The intrinsic structural feature of ytterbium fluoride compounds and four external factors, namely the pH values in the initial reaction solution, the fluoride source, the use of an organic additive (Cit3−) and simple ions (Na+, NH4+, BF4−, BO3−), are responsible for the ultimate shape evolutions of the products. The possible formation mechanisms for products with various architectures are presented. Additionally, the upconversion (UC) photoluminescence properties of β-NaYbF4:Er3+ hexagonal microdisks, microtubes, α-NaYbF4 spheres and YbF3 octahedra were investigated in detail. To the best of our knowledge, this is the first report concerning controllable synthesis of ytterbium fluoride compounds with diverse crystal phases and morphologies. More importantly, this simple method is expected to allow the large-scale production of other complex rare earth fluoride compounds with controllable morphologies and sizes, and exploration of the morphology and phase-dependent photoluminescence properties.

Phase dependent photoluminescence and energy transfer in Ca 2P 2O 7: Eu 2+, Mn 2+ phosphors for white LEDs

α- and β-Ca 2P 2O 7: Eu 2+, Mn 2+ phosphors were prepared by solid-state reaction. Phase transition from tetragonal (β-phase) to monoclinic (α-phase) is performed. A strong orange emission of Mn 2+ is observed in both α-and β-Ca 2P 2O 7: Eu 2+, Mn 2+ upon near ultraviolet (UV) excitation through energy transfer from Eu 2+ to Mn 2+. The transfer efficiencies for various Mn 2+ concentrations are estimated based on lifetime measurements of the fluorescence of Eu 2+ in the two phases. The photoluminescence excitation spectra of α-Ca 2P 2O 7: Eu 2+, Mn 2+ can cover 400 nm of the near-UV range, denoting its potential use as a phosphor with intense orange component for white light emitting diodes (LEDs).

Surface morphology and crystalline phase dependent photoluminescence of Gd2O3:Eu3+ thin films grown on various substrates

Gd2O3:Eu3+ luminescent thin films have been grown on Al2O3 (0001), Si (100) and fused silica glass substrates using pulsed laser deposition technique. By changing substrate, the films show different crystalline phases, surface morphologies and luminescent characteristics. Both cubic and monoclinic phases were observed from the Gd2O3:Eu3+ films grown on all substrates. Crystalline phase and surface roughness of the films are very sensitive to the type of substrate and photoluminescence intensity of the Gd2O3:Eu3+ films are highly dependent not only on the crystallinity but also on the surface roughness of the films. Especially, the photoluminescence intensity is sensitive to the intensity of monoclinic phase of Gd2O3:Eu3+ films. The highest emission intensity was observed with Gd2O3:Eu3+ films grown on Al2O3 (0001) substrate, whose brightness was 2.7 and 3.8 times higher than that of the films grown on Si (100) and fused silica glass substrates, respectively. It is indicated that Al2O3 (0001) substrate supports better the cubic phase of Gd2O3:Eu3+ films and rougher surface roughness than any other substrates.