Room Temperature Photoluminescence Properties Research Articles

Development of Highest Value of the Measured Efficiency of Mesoporous Petal Shaped Europium (III) Doped Cobalt Tetroxide@Cupric Oxide Hybrid Nanomaterials for Enhanced Room Temperature Photoluminescence and Fluorescence Decay Properties.

In our work, a novel series of europium (III) (Eu3+) (5, 10 and 15 wt %) doped cobalt tetroxide@cupric oxide (Co3O4@CuO) nanomaterials (NMs) were synthesized by facile coprecipitation method. The synthesized NMs were characterized by XRD (X-ray diffraction), FT-IR (Fourier transform infrared), UV (ultraviolet)-visible absorption spectra, XPS (X-ray photoelectron), BET (Brunauer-Emmett-Teller) analytical methods. Crystal structure studies revealed the formation of polycrystalline nature with monoclinic and cubic phase. The morphology studies of Eu3+x:Co3O4@CuO (x = 5, 10 and 15 wt %) showed petal shape nanoparticles (NPs) with agglomeration. Redshift in optical absorption spectra appeared with a significant impact on the optical band gap as Eu3+ concentration increases on Co3O4@CuO bimetallic oxide NMs. The chemical composition and valence state of the elements confirmed from XPS studies detected the presence of Eu, Cu, Co, O and C elements. An increase in the pore size and surface area resulted as the Eu3+ concentration increased on Co3O4@CuO NMs. However, room temperature photoluminescence (RTPL) spectra of Co3O4@CuO bimetallic oxide NMs at two different excitations (λ excitation = 280nm, 320nm) showed sharp, strong emission intensities located at near ultraviolet (NUV) region and weak emissions detected at far ultraviolet (FUV) regions of the RTPL spectrum. Further, visible range emission intensities were displayed by Eu3+:Co3O4@CuO (5, 10 and 15 wt %) NMs when exited at 280nm. The characteristic white light emission peaks in the visible range of the RTPL spectra showed intense blue, green and orange colours. Emission intensity increases with an increase in Eu3+ concentration on Co3O4@CuO bimetallic oxide NMs. The fluorescence (FL) decay spectra of Eu3+ 10wt% and 15 wt%: Co3O4@CuO NMs showed a decay lifetime of 2.54 and 2.31ns (ns) attributed to the dynamic, ultrafast excitation energy transfer between Eu3+ (dopant) and Co3O4@CuO (host) NMs. It is proposed that enhanced RTPL emission intensity and FL decay behavior of Eu3+x:Co3O4@CuO NMs closely related to the change in the optical band gap, variation in the crystallite size, formation of more number of oxygen vacancies in the crystal structure of hybrid nanomaterials.

Nanoporous GaN by selective area sublimation through an epitaxial nanomask: AlN versus Si x N y

Nanoporous GaN layers were fabricated using selective area sublimation through a self-organized AlN nanomask in a molecular beam epitaxy reactor. The obtained pore morphology, density and size were measured using plan-view and cross-section scanning electron microscopy experiments. It was found that the porosity of the GaN layers could be adjusted from 0.04 to 0.9 by changing the AlN nanomask thickness and sublimation conditions. The room temperature photoluminescence properties as a function of the porosity were analysed. In particular, a strong improvement (>100) of the room temperature photoluminescence intensity was observed for porous GaN layers with a porosity in the 0.4–0.65 range. The characteristics of these porous layers were compared to those obtained with a Si x N y nanomask. Furthermore, the regrowth of p-type GaN on light emitting diode structures made porous by using either an AlN or a Si x N y nanomask were compared.

Large room-temperature ferromagnetism in ordered porous In2O3 films

In this paper, ordered porous In2O3 films were prepared on ordered porous Al2O3 thin films by magnetron sputtering. The film shows large room-temperature ferromagnetism of 18.78 emu/cm3, and the saturation magnetization is more than ten times larger than in the dense In2O3 film. Moreover, the magnetic anisotropy of the ordered porous In2O3 film was observed, and the saturation magnetization in the direction perpendicular to the film surface is much greater than in the direction parallel to the film surface. In addition, by investigating the room-temperature ferromagnetism and photoluminescence properties of the film under different environments, the room-temperature ferromagnetism of ordered porous In2O3 films is most affected by the oxygen vacancies. The research in this paper provides a solid basis for the development of spintronic devices.

The UV photodetection enhancement of tailored ZnO nanorods by controlling the aspect ratio

ZnO Nanorods (NRs) are deposited on glass substrate using the hydrothermal method by applying a strategic growth control to improve their aspect ratios. In this research, the aspect ratio was tuned by tailoring the synthesis parameters, including the seed layer annealing temperature, absence/presence of polyethylenimine (PEI) in the growth solution, and the solution preheating process. The effects of these parameters on the morphology, crystal structure, room temperature photoluminescence properties, and current-voltage characteristics were examined by FESEM, XRD, PL, and I-V measurements. It was demonstrated that by varying the seed layer annealing temperature and presence of PEI solution as well as implementation of the solution preheating process, the aspect ratio of the NRs was increased from 7.9 to 64.4. The ZnO NRs with the high aspect ratio of 64.4, achieved from the solution containing PEI additive preheated at 95 °C for 1 h on the ZnO seed layer annealed at 250 °C that exhibited a maximum bandgap energy (3.32 eV), the highest responsivity of 4.5 mA/W, and the shortest response time (1.1 s). The UV photo detection performance of the deposited NR was improved by enhancing their aspect ratios. Finally, from the application point of view, the optimum value of responsivity is significantly increased to 44.1 mA/W using the deposited nanorods in the FTO/ZnO NRs/FTO device structure.

Effect of electrical poling on the structural, dielectric and photoluminescence properties of small concentration of Ho+3 substituted NBT

The effect of electrical poling on the room temperature structural, dielectric and photoluminescence properties of small concentration (i.e. 0.5 mole%) of Ho+3 substituted sodium bismuth titanate ferroelectric material (Na0.5Bi0.495Ho0.005TiO3 abbreviated as NBT-0.5Ho) has been investigated. Its crystal structure was found to be the mixture of two phases of rhombohedral (R3c) and monoclinic (Cc) in which monoclinic (Cc) coexisted as major phase. Comparative study of X-ray diffraction (XRD) patterns of electrically poled and unpoled specimens of NBT-0.5Ho revealed that electric field irreversibly transformed crystal structural of dominant Cc (≈-94.05% phase fraction) phase to R3c (≈70.6% phase fraction) as major phase. Dielectric value and its dispersion with frequency were significantly decreased in poled specimen which is ascribed to electric field driven structural change. Two photoluminescence (PL) emissions at 655nm and 756nm were obtained in NBT-0.5Ho. PL intensity was considerably tuned in effect of electrical poling in term of quenching. Obtain quenching is correlated with induced structural ordering towards higher symmetry phase (R3c) in effect of electric poling which is confirmed from XRD analysis. Obtained additional functionality of photoluminescence in the NBT-0.5Ho ferroelectric material and its tuning in effect of electric field opens the possibility in the material for optoelectronic devices applications.

(Invited) Impact of Boron Doping and H2 Annealing on Light Emission from Ge/Si Core-Shell Quantum Dots

We have fabricated Si-QDs with boron-doped Ge core with an areal density as high as ~1011 cm-2 on ultrathin SiO2 and characterized their room temperature photoluminescence (PL) properties. With B doping to the Ge core, stable PL observed in the energy range of 0.62 - 0.85 eV was increased by a factor of ~1.5. Note that a new relatively-narrow component peaked at ~0.64 eV emerges in addition to four components derived from the spectral deconvolution of the PL spectrum of undoped QDs and is attributable to radiative recombination between the first quantized state in the conduction band of the Si clad and the B-acceptor level in the Ge core. With H2 post-anneal at 100°C, the integrated PL intensity of the B-doped QDs was reduced by ~35% and the 0.64 eV component disappeared. With increasing H2 post-anneal temperature up to 350°C, the PL intensity was increased to ~1.4 times the initial intensity before post-annealing, and the 0.64 eV component was recovered. The observed PL changes with post-anneal are attributable to hydrogen-induced passivation of B acceptors at 100°C and thermal dissociation of B-H complex at higher temperatures up to 350°C accompanied with hydrogen passivation of residual dangling bond defects as seen in the undoped case.

Enhancing the Photoluminescence Property of Pr3+ Ions by Understanding the Polymorphous Influence of the K3Lu(PO4)2 Host.

Adjusting the local coordination environment of lanthanide luminescent ions is a useful method to manipulate the relevant photoluminescence (PL) property. K3Lu(PO4)2 is a phase-change material, and according to the stable temperature range from low to high, the related polymorphs are phase I [P21/m, coordination number (CN) of Lu3+ = 7], phase II (P21/m, CN = 6), and phase III (P3̅, CN = 6), respectively. Based on the temperature-dependent PL analysis of K3Lu(PO4)2:Pr3+, we find that Pr3+ ions occupy the noninversion sites (Cs) in the two low-temperature phases but preferentially enter into the inversion ones (C3i) in phase III. Compared to Pr3+-doped phase I (78 K), Pr3+ ions in phase III (300 K) manifest a weaker fluorescence intensity (170-fold lower). To enhance the room-temperature PL property of K3Lu(PO4)2:Pr3+, a polymorphous adjustment strategy was proposed by the use of the ion-doping method. By introducing the Gd3+ ions into the lattice, Pr3+-doped phase I is successfully stabilized to room temperature, manifesting a 27-fold fluorescence increase in comparison to K3Lu(PO4)2:Pr3+ (0.1 at. %). The finding discussed in this study highlights the significance of site engineering for luminescent ions and also presents the application value of phase-change hosts in the development of high-performance luminescent materials.

Luminescence properties of CaMoO4 nanoparticles embedded borate composite glass

Transparent glasses of the 1.2CaO–0.2MoO3–B2O3 system were fabricated using the conventional melt-quenching technique. The glasses were heat-treated above the glass transition temperature (Tg) to yielded nanocrystalline composites of CaMoO4 (CMO) and CaB2O4 (CBO). The structural characterization of as-quenched and heat-treated glasses corroborated the crystallites of CaMoO4 and CaB2O4 using powder X-ray diffraction (XRD) and Raman spectroscopy. The various morphologies of the samples were studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Optical transmittance spectrum for as-quenched glass shows, approximately, 77% transparency (uncorrected for the reflection losses) from 2600 ​nm to 325 ​nm with a lower cut-off wavelength at 324 ​nm. The optical band gap (Eg) and refractive index (η) of the as-quenched transparent glass were found to be 3.43 ​eV and 1.615, respectively. Room-temperature photoluminescence properties of the as-quenched and glass nanocrystal composites (GNC) exhibit broad blue emission with UV excitation wavelengths (using laser and Xe lamp). Such distribution of CMO crystallites of nano-dimensions embedded in borate glass matrix could be used for various PL applications.

Synthesis and luminescence spectroscopy study of a novel orange-red colour emissions phosphor based on Tb3+ ion-doped Na2 ZnP2 O7.

Here, we report the synthesis and study of new orange-red (OR) colour-emitting phosphors Na2 ZnP2 O7 :xTb3+ (x = 1, 1.25, 1.5, and 1.75 mol%) using a conventional solid-state reaction. The sample crystallographic structures and their room temperature photoluminescence properties were measured using X-ray powder diffraction, excitation and emission spectra, as well as emission decay curves. X-ray diffraction analysis showed an isostructural tetragonal structure for all the doped materials with no impurities. Several colour emissions corresponding to 5 D4 →7 F6 (blue), 5 D4 →7 F5 (green), 5 D4 →7 F4 (orange) and 5 D4 →7 F3,2,0 (red) intraconfigurational transitions were observed and investigated. These colours were dominated by the OR colours. 5 D4 energy level lifetime was independent of Tb3+ concentration. Various radiative and luminescence parameters, such as experimental branching ratio, radiative decay rate, and luminescence quantum efficiencies, were calculated and discussed. Chromaticity diagram calculations illustrated an orange emission for all the studied materials.

Optical properties of neodymium ions in nanoscale regions of gallium nitride: erratum

Wide bandgap semiconductors are increasingly important for bioimaging applications, as they can possess good biocompatibility and host a large range of fluorescent defects spanning the visible to infrared. Gallium nitride is one promising host for photostable fluorophores. In particular, neodymium (Nd)-doped gallium nitride (GaN) shows bright near-infrared fluorescence and narrow room temperature linewidth and is therefore a candidate material for fluorescent probes for bioimaging. To explore the conditions necessary to generate biomarkers based on Nd:GaN, this paper reports the room temperature photoluminescence (PL) properties of small ensembles of Nd ions implanted into the nanoscale regions of GaN epilayers. The minimum volume of Nd-implanted GaN that can be optically detected in this study is about 8×104 nm3 and the minimum detected ensemble of Nd ions is about 4×103, although not all of implanted Nd ions activate as luminescence centers. We show from the PL excitation spectra that the strongest resonant excitation appears at 619 nm, attributed to the 4I9/2 → 4G5/2 (4G7/2) transition in the 4f-shell. We measure the luminescence lifetime to be several tens of microseconds. We also identify the presence of a different excitation mechanism from the resonant excitation when excited below 510 nm (above 2.43 eV).

Optical properties of neodymium ions in nanoscale regions of gallium nitride

Wide bandgap semiconductors are increasingly important for bioimaging applications, as they can possess good biocompatibility and host a large range of fluorescent defects spanning the visible to infrared. Gallium nitride is one promising host for photostable fluorophores. In particular, neodymium (Nd)-doped gallium nitride (GaN) shows bright near-infrared fluorescence and narrow room temperature linewidth and is therefore a candidate material for fluorescent probes for bioimaging. To explore the conditions necessary to generate biomarkers based on Nd:GaN, this paper reports the room temperature photoluminescence (PL) properties of small ensembles of Nd ions implanted into the nanoscale regions of GaN epilayers. The minimum volume of Nd-implanted GaN that can be optically detected in this study is about 8×104 nm3 and the minimum detected ensemble of Nd ions is about 4×103, although not all of implanted Nd ions activate as luminescence centers. We show from the PL excitation spectra that the strongest resonant excitation appears at 619 nm, attributed to the 4I9/2 → 4G5/2 (4G7/2) transition in the 4f-shell. We measure the luminescence lifetime to be several tens of microseconds. We also identify the presence of a different excitation mechanism from the resonant excitation when excited below 510 nm (above 2.43 eV).

Spectroscopic and color chromaticity analysis of rhodamine 6G dye-doped PVA polymer composites for color tuning applications

Herein we report the successful fabrication of highly flexible, reversibly stretchable and transparent rhodamine 6G/poly(vinyl alcohol) (Rh6G/PVA) polymer composite (PC) films using a user-friendly solution casting method by adding different amounts, viz. 0, 0.5, 1, 1.5 and 2 wt%, of Rh6G dye. The FTIR studies reveal that an interaction between PVA matrix and added Rh6G dye and room-temperature photoluminescence (RTPL) emission intensity is decreased with the increase in the Tg is observed from DSC thermograms. The developed films show appreciable optical and RTPL properties as established by a UV–visible and fluorescence techniques such that the electronic spectral studies substantiate the changes in electronic band structure of PC films, leading to appreciable changes in the optoelectronic properties. These prepared films with excellent optoelectronic properties alongside appreciable flexibilities and stretchabilities aid their applications to organic light emitting diodes (OLED) with enhanced RTPL studies.

Effects of tungsten doping on structure and photoluminescence of MoO3–x nanomaterials

The challenge in molybdenum oxides intended for integration into electronic, optical, energy conversion, and other devices is tuning of their photoluminescence (PL) properties. Despite some initial studies on possibilities of tuning PL properties, this issue remains unresolved. For this reason, we explored the tailoring of PL properties of molybdenum oxide nanomaterials with a dopant through a robust synthesis by hot filament chemical vapour deposition. Here the MoO3–x nanomaterials are doped with tungsten in a low concentration, and the room temperature PL properties are studied. The obtained results highlight the interaction of Mo5+ defects and oxygen vacancies, which are playing an essential role in the enhancement of green PL emission. Moreover, the used doping method is fast and straightforward and can be used to control the structure as well as the PL properties of molybdenum oxide nanomaterials.

Room-temperature photoluminescence and electroluminescence of 1.3-μm-range BGaInAs quantum wells on GaAs substrates

We report the room temperature photoluminescence and electroluminescence properties of boron incorporated into highly strained InGaAs, forming BGaInAs, grown on GaAs substrates. X-ray diffraction was used to determine the alloy composition and strain of BGaInAs quantum wells on GaAs. As expected, the addition of boron reduced the quantum well compressive strain, preventing strain-relaxation and enabling extension of the peak emission wavelength of InGaAs quantum wells to 1.3 μm on GaAs. We also report both the longest wavelength emission observed from BGaInAs (1.4 μm) and electrically injected photoemission from a dilute-boride active region. We observed a blueshift in electroluminescence, due to unintentional in situ annealing of the active region, which we mitigated to demonstrate a path to realize true 1.3 μm emitters in the presence of in situ annealing.

Thermally static stokes fluorescence based self and Sm3+ activated SrWO4 luminophores for application in LED and visual display unit

Ceramic samples of pure and Sm3+ activated SrWO4 luminophores have been synthesized by solid state reaction technique. The confirmation of the sample formation is obtained by analysing and comparing the XRD data with standard JCPDS data. The material shows the single tetragonal phase with space group I41/a. The surface morphology is analysed by Field Emission Scanning Electron Microscope. The interacting behavior of the prepared material with UV and visible light is studied by recording the data in the diffuse reflectance mode to calculate the optical band gap using UV–Visible Spectrophotometer. The room temperature photoluminescence property of the material is studied by recording the excitation and emission spectra along with the decay kinetics. The PL emission spectra contain the emission peaks of the host due to structural defect of the lattice as well as the emission peaks of Sm3+ ions due to its f-f transitions. To check the high temperature utility of the material, temperature dependent photoluminescence property is studied very cautiously by joining the temperature control setup (Optistate DN2 (Oxford instrumental)) to the sample chamber. The luminescence intensity does not degrade much, as the temperature increases from room temperature to 475 K. The photometric study reveals the color-tunable emission of the material from deep blue to light blue region.

Impact of Na2-EDTA and urea on structure and optical properties of pure neodymium oxide

Nano pebbles of pure neodymium oxide is synthesized by the solution combustion method and they exhibit room temperature photoluminescence and thermoluminescence properties. Powder X-ray diffraction pattern reveals A-type hexagonal structure. Surface morphology is visualized by the field emission scanning electron microscopy. The visualized images are regular and irregular shapes with smooth surface. Energy dispersive X-ray spectroscopy reveals the existence of Nd, O and Na elements. X-ray photoelectron spectroscopy reveals the signature of all elements exist in the sample. The diffused reflectance spectrum is used to evaluate the optical band gap energy. Fourier transformed-infrared spectrum confirms the existence of Nd and O bond. Raman spectrum peaks are assigned and confirms A-type hexagonal phase. PL emission is observed in UV, blue, green and red region and the peaks are located at 325, 347, 380, 385, 422, 445, 485, 530, 605, 625, 650, 690 and 750 nm. The activation energies and the frequency factors of thermoluminescence are calculated. The synthesized Nd2O3 is a promising material for white light emitting diodes and the supra linearity features of TL is to be a potential candidate for dosimeters applications.

Combined Temperature and Pressure Sensing Using Luminescent NaBiF4:Yb,Er Nanoparticles

The room temperature synthesis and photoluminescence properties of hexagonal phase NaBiF4 nanocrystals doped with lanthanide ions have been presented. An efficient infrared Stokes emission and upco...

Multifunctional ZnO nanorods decorated with plasmonic gold nanoparticles for enhanced room temperature field emission, photo-luminescence and catalytic properties

We report the enhancement of room temperature photoluminescence (PL), field emission and photocatalytic properties of ZnO nanorods (NRs) decorated by gold NPs (Au-ZnO NRs) prepared using hydrothermal process. The results of X-ray diffraction (XRD) analysis confirmed formation of gold NPs (NPs) and wurtzite phase of ZnO in the final nanostructures. Microscopic studies revealed that uniform ZnO NRs were formed and gold NPs are well decorated on the surface of the NRs. It was shown that both reaction time and concentration of HAuCl4 play a crucial role in photocatalytic, field emission and PL properties of Au-ZnO NRs. We suggest that there is a correlation between the shape of the NRs and concentration of HAuCl4 which causes the maximum PL intensity and stronger field emission properties. The ultraviolet (UV) and visible-light photocatalytic performance was successfully demonstrated for the photodegradation of Methylene blue (MB) as a model dye. Field emission studies revealed that by introducing gold NPs into the ZnO NRs the emission current increases. We have found that the shape of the nanostructure has a crucial role in the field emission properties and at higher reaction times, where the aspect ratio of the ZnO NRs decreases, the emission current also decreases.

A Series of Lanthanide-Based Metal-Organic Frameworks Derived from Furan-2,5-dicarboxylate and Glutarate: Structure-Corroborated Density Functional Theory Study, Magnetocaloric Effect, Slow Relaxation of Magnetization, and Luminescent Properties.

Herein, through a dual-ligand strategy, we report eight isorecticular lanthanide(III) furan-2,5-dicarboxylic acid metal-organic frameworks (Ln-MOFs) with the general formula {[Ln(2,5-FDA)0.5(Glu)(H2O)2]· xH2O} n [Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), and Yb (8); 2,5-FDA2- = furan-2,5-dicarboxylate and Glu2- = glutarate; x = 0.5 for 1, 2, and 4 and x = 0 for 3 and 5-8], synthesized under solvothermal conditions by using an N, N'-dimethylformamide/H2O mixed solvent system. Crystallographic data reveal that all eight Ln-MOFs 1-8 crystallize in the orthorhombic Pnma space group. All of the MOFs are isostructural as well as isomorphous with distorted monocapped square-antiprismatic geometry around the Ln1 metal center. In Ln-MOFs 1-8, the 2,5-FDA2- and Glu2- ligands exhibit μ2-κ4,η1:η1:η1:η1 and μ3-κ5,η2:η1:η1:η1 coordination modes, respectively. Topologically, assembled Ln-MOFs 1-8 consist of the 2D cem topological type. The designed Ln-MOFs 1-8 are further explored for structure-corroborated density functional theory study. Meanwhile, room temperature photoluminescence properties of Ln-MOFs 2 and 4 and magnetic properties of Ln-MOFs 3 and 5 have been explored in detail. A highly intense, ligand-sensitized, Ln3+ f-f photoluminescence emission is exhibited by Ln-MOFs 2 [Eu3+ (red emission)] and 4 [Tb3+ (green emission)]. Magnetic studies suggest weak antiferro- and ferromagnetic interactions between adjacent GdIII ions in Ln-MOF 3, thereby displaying a large magnetocaloric effect. The magnetic data measured at T = 2 K and Δ H = 30 kOe depict that the -Δ Sm value per unit mass reaches 32.1 J kg-1 K-1, which is larger than most of the GdIII-based complexes reported. The alternating-current susceptibility measurements on Ln-MOF 5 revealed that out-of-phase signals are frequency- and temperature-dependent under both 0 and 2 kOe direct-current fields, thereby suggesting a typical slow magnetic relaxation behavior with two relaxation processes. This is further supported by the Cole-Cole plots at 2.4-6 K.

ZnO nanostructure-assisted growth of (0002)-oriented GaN thin films by laser molecular beam epitaxy

Vertically aligned zinc oxide (ZnO) nanostructures (NS) have been fabricated without any catalyst on Si (100) and sapphire (0002) substrates using high-pressure-assisted pulsed laser deposition technique. It has been observed that the substrate plays a crucial role in deciding the morphology and optical quality of the nanostructures, wherein ZnO NS on Si substrate exhibit better luminescence characteristics as compared to those grown on sapphire substrate. Gallium nitride (GaN) layers are grown using a customized laser molecular beam epitaxy system and the effect of an intermediate layer in the form of vertically aligned ZnO NS is analyzed. A comparative study is performed with GaN layers grown on ZnO NS-coated Si, bare Si, and bare sapphire substrate. The structural and room temperature photoluminescence properties of the GaN layer significantly improve when grown on ZnO-NS/Si substrates as compared to bare sapphire and Si substrate.