High Luminescence Intensity Research Articles

Luminescence Optimization of M3MgSi2O8 : Eu2 + Phosphor by Spray Pyrolysis Combined with Combinatorial Chemistry for UV-LED Application

Spray pyrolysis was applied to prepare -doped phosphor for near-ultraviolet (NUV) light-emitting diode (LED) application. The luminescence characteristics were optimized by a combinatorial screening method combined with spray pyrolysis for the Ca–Sr–Ba ternary system. The first composition library was obtained by measuring the emission spectrum under 395 NUV excitation. In this first screening, the highest luminescence intensity was obtained at , which had 48% enhancement in the integrated emission intensity compared with phosphor. The second screening was conducted for the potential compositions in the first library. As a result, the optimized composition was , which showed 170% enhancement in the integrated emission intensity compared with phosphor.

Solvothermal Route to Colloidal Upconverting NaYF<SUB>4</SUB>: Yb<SUP>3+</SUP>/Er<SUP>3+</SUP> and Yb<SUP>3+</SUP>/Tm<SUP>3+</SUP> Nanocrystals

Monodispersed nanocrystals of NaYF4: Yb3+, Er3+/Tm3+ that exhibited a high luminescence intensity were chemically synthesized by a non-aqueous solvothermal approach. These nanocrystals were easily dispersed in non-polar solvent and subsequently formed a transparent colloidal solution. Under 980 nm NIR excitation, green and blue emissions were observed from colloidal solutions of the NaYF4: Yb3+, Er3+/Tm3+, respectively. The effects of different solvents used and solvent concentration on the shape, size and size distribution of the nanocrystals have been investigated. It has been revealed that the doping ions diffused into NaYF4 lattice, and they formed a solid solution. The fluorescence photos, spectra, luminescence mechanism, and the formation mechanism of the nanocrystals have also been demonstrated. Emission spectrums of the nanocrystals prepared by this method show much more complicated emission peaks than by other methods.

Luminescence enhancement of Eu-doped calcium magnesium silicate blue phosphor for UV-LED application

(Ca 1− x ,Eu x )MgSi 2 y O 6+ δ blue phosphor was prepared by spray pyrolysis and the photoluminescence properties were optimized by controlling concentration of Si element and the activator content. At y=1.0, the concentration quenching in the luminescent intensity appeared when the Eu 2+ content ( x) was 0.01 (1 at%). Such quenching concentration was changed with the concentration of silicon ( y), which was increased with an increase in the quantity of excess Si ( y>1.0). The highest luminescent intensity was achieved when the Eu 2+ content ( x) and the Si concentration ( y) were 0.04 and 1.3, respectively. According to X-ray diffraction (XRD) analysis, the tetragonal SiO 2 phase was formed as a minor phase when the y value was larger than 1.3. The formation of SiO 2 phase, however, did not reduce but increased the luminescent intensity when the Eu 2+ content was optimized again. As a result, the luminescent intensity of the phosphor particles optimized in the content of both Si and Eu 2+ was about 150% improved compared with that of the CaMgSi 2O 6:Eu sample ( x=0.01, y=1.0).

Effects of Particle Size and Type of Alumina on the Morphology and Photoluminescence Properties of Sr4Al14O25:Eu2+/Dy3+ Phosphor

Sr4Al14O25:Eu2+/Dy3+ phosphor with high luminescence intensity and long afterglow duration was synthesized using 1.0 μm (α), 0.1 μm (α), and 0.05 μm (γ) particle sizes of Al2O3. SEM observation results showed that spike‐like thin particles were formed when 0.05 μm γ‐Al2O3 was used as raw material. Hexagonal thick particles were observed when 0.1 μm α‐Al2O3 was used. But irregular, thin particles were observed while using 1 μm α‐Al2O3. Photoluminescence measurements showed that both the initial intensity and the long persistency were much higher for the phosphor prepared using γ‐Al2O3 of 0.05 μm particle size.

Roughness effect on photoluminescence of cerium doped zinc oxide thin films

Undoped and cerium doped zinc oxide thin films have been prepared by spray pyrolysis technique. The influence of Ce as doping agent on the optical and nonlinear optical properties was carefully investigated using transmission, X-ray diffraction, photoluminescence, atomic force microscopy (AFM), and third harmonic generation (THG). It has been found a deep correlation between the surface roughness and the optical properties. In fact the roughness deteriorates the luminescence and nonlinear response, in a sense that the highest luminescence intensity and nonlinear susceptibility χ (3) are obtained for the smoothest layer. Doped layers are characterized with a high visible luminescence, attributed to cerium transitions, and susceptibilities in the range of 6.38 × 10 −13 esu.

Effects of SiC buffer on the structural and photoelectrical properties of ZnO thin films grown on Si(1 1 1) by PLD

The films of ZnO/SiC/Si(1 1 1) and ZnO/Si(1 1 1) were grown by the pulsed-laser-deposition (PLD) technique and were processed to fabricate ultraviolet (UV) detectors. The effects of SiC buffer on the structural and photoelectrical properties of ZnO thin films grown on Si(1 1 1) substrates were investigated by the X-ray diffraction (XRD), photoluminescence (PL), current–voltage ( I– V) and photoresponse measurements. The results show that the SiC buffer not only leads to better crystalline quality and higher intensity of luminescence at 380 nm of ZnO thin film, but induces lower leakage current and much better photoresponse of UV detector. A compliant SiC buffer layer can relax partial stress induced by large lattice and thermal mismatch between ZnO and Si and reduce the interface defects and interface state density, which can effectively improve the crystalline quality as well as optical and photoelectrical properties of the ZnO thin film grown on Si substrate.

Microwave synthesis of manganese-ion-doped zinc sulfide nano-phosphors using a novel monomer

ZnS:Mn 2+ nano-phosphors are synthesized via a microwave irradiation technique using zinc 2-ethylhexanoate as a novel zinc precursor. The developed process produces ZnS:Mn 2+ nano-particles having in situ capping of 2-ethylhexanoic acid on the surface, resulting in high luminescence intensity due to effective surface passivation. Surface characterization of the nano-particles indicates that 2-ethylhexanoic acid is chemisorbed as carboxylate onto the surface of ZnS:Mn 2+ nano-particles and the two oxygen atoms in the carboxylate are coordinated symmetrically to the Zn atoms, leading to the formation of the covalent Zn–O bond. The anion bound onto the nano-particle surface prevents particle agglomeration due to electrostatic repulsion between two adjacent particles. Electron spin resonance (ESR) spectrum showed a hyperfine sextet revealing the fact that Mn 2+ in ZnS was present as dispersed Mn 2+ impurities rather than Mn 2+ clusters, which would produce broad resonance without splitting. The samples showed bright yellow-orange luminescence at about 585 nm, characteristic of 4T 1 (excited) → 6A 1 (ground) transition of Mn 2+ ion at T d symmetry in ZnS.

Vacuum Ultraviolet and Ultraviolet Spectroscopy of Tb3+- and Eu3+-Doped Na(Sr,Ba)PO4 Phosphate

The Eu3+- and Tb3+-doped NaSr0.65Ba0.35(PO4) phosphors were prepared by high-temperature solid-state reaction. X-ray powder diffraction (XRD) analyses confirm the pure crystalline phase of Olgite mineral. Scanning electron microscopy (SEM) measurements indicate that these phosphors have good surface-crystalline with a narrow size distribution. Vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) spectroscopy were applied to study the luminescence properties of these phosphors. The bands near 147 nm in the VUV excitation spectra of those doped samples are attributed to the PO43- absorption in the host. The excitation and emission spectra indicate that the phosphors can be effectively excited for NaSr0.65Ba0.35(PO4):Eu3+ and NaSr0.65Ba0.35(PO4):Tb3+ by 147 nm and exhibit a red and green light, respectively. The Commission International de I'Eclairage (CIE) chromaticity coordinates for Eu3+- and Tb3+-activated phosphors are calculated. Considering the high luminescence intensity, excellent color purity and chemical stability, NaSr0.65Ba0.35(PO4):RE (RE = Eu3+, Tb3+) are attractive red- and green-emitting plasma display panel phosphors.

Self-assembled one-pot synthesis of red luminescent CdS:Mn/Mn(OH) 2 nanoparticles

We report a novel method of growing red luminescent (635 nm) Mn-doped CdS (CdS:Mn) nanoparticles capped by an inorganic shell of Mn(OH) 2. CdSO 4, Na 2S 2O 3 and Mn(NO 3) 2 were used as the precursors, and thioglycerol (C 3H 8O 2S) was employed as the capping agent and also the catalyst of the reaction. Using these materials resulted in very slow rate of the reaction and particles growth. The self-assembled one-pot process was performed at pH of 8 and Mn:Cd ratio of 10, and took about 10 days for completion. CdS:Mn nanoparticles are slowly formed in the first day of the process; however, the luminescence is weak. After 7 days, the solution turns white turbid through the formation of additional particles, which precipitate on the walls on the next day. At this stage, a relatively strong red luminescence at 635 nm appears from transparent solution of the CdS:Mn nanoparticles. The white deposit on the walls turns to dark-brown color and luminescence increases on the 9th day. Finally, the CdS:Mn nanoparticles agglomerate and precipitate out of the solution on 10th day. X-ray diffraction and optical spectroscopy showed crystalline phase CdS nanoparticles with an average size of 3.6 nm. We explain the luminescence enhancement based on the formation of a Mn(OH) 2 shell on the surface of the CdS:Mn nanoparticles during the precipitation stage. This can passivate the S dangling bonds located on the particles surface. As the surface Cd sites are previously capped with thioglycerol molecules, a complete surface passivation is achieved and results in emergence of high-intensity luminescence.

기계 화학적 방법을 통한 Eu3+도핑된 (Y,Gd)BO3형광체의 분말제조

The mechanochemical process were employed to prepare the red phosphors (Y,Gd)<TEX>$BO_3:Eu^{3+}$</TEX>. The main factors affecting particle size, particle distribution, and luminescent properties of the product were investigated in details. Particles sized around 200-600 nm are formed after intensive milling. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum. Results revealed that phosphors with different morphology, small particle size and high luminescence intensity could be obtained by mechanochemical process.

Phase Purity and Luminescence Properties of Fine Ca-α-SiAlON : Eu Phosphors Synthesized by Gas Reduction Nitridation Method

This paper reports a simple, inexpensive, and efficient synthetic route to -based yellow phosphors for white light-emitting diodes. Through direct gas reduction and nitridation of the homogeneous oxide precursor of , fine phosphors were obtained by one-step firing at for 4 h in the flowing and mixture gas. The dependence of the structural characterization and optical properties on the overall composition of the host lattice has been investigated. A nearly single-phase can be synthesized by controlling the overall composition of the host lattice at and . The strongest luminescence is achieved at about and . Further improvement of the powder characteristics was attained by post heat-treatment at for 2 h under 5 atm of by gas-pressure sintering. The post-treated powders showed a pure phase at . The phosphor exhibits a high crystallinity, high luminescence intensity, high quantum efficiency, and very low thermal quenching, which is better than those prepared by the conventional solid-state reaction.

Cerium-Doped Lutetium Aluminum Garnet Phosphors and Optically Transparent Ceramics Prepared from Powder Precursors by a Urea Homogeneous Precipitation Method

Nanosized, purified crystalline-phase cerium-doped lutetium aluminum garnet (LuAG:Ce) phosphors were prepared by the urea homogeneous precipitation method. The obtained phosphors showed much higher dispersivity, a fairly uniform size of about 30 nm, and higher luminescence intensity than those synthesized by a sol–gel combustion process. The radioluminescence spectrum of the phosphors consisted of two emission bands owing to the transitions from the lowest 5d excited state to the 4f ground state of Ce3+. The transmittance in the visible light region of the transparent ceramics fabricated at 1800 °C for 10 h under a higher vacuum of 1.5×10-3 Pa using the prepared powders reached 70% and the attenuation coefficient decreased to 0.116 mm-1, which caused much higher luminescence intensity. Compared with those reported previously, the optical properties of the LuAG:Ce transparent ceramics fabricated in the present work improved markedly.

GaN doped with neodymium by plasma-assisted molecular beam epitaxy

We report in situ doping of GaN with the rare earth element Nd by plasma-assisted molecular beam epitaxy. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectroscopy data indicate ∼5at.% Nd in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation under nitrogen-rich conditions with up to ∼1at.% Nd, with the highest luminescence intensities corresponding to doping of ∼0.5at.%. Spectral correlation of the Nd emission multiplets for above (325nm) and below (836nm) GaN bandgap excitations implies enhanced substitutional doping at the Ga site.

GaN Doped with Neodymium by Plasma-Assisted Molecular Beam Epitaxy for Potential Lasing Applications

AbstractWe provide an investigation of in situ doping of GaN with the RE element Nd by plasma assisted-molecular beam epitaxy (PA-MBE). GaN epilayers are grown on c-plane sapphire and free standing GaN substrates and the Nd doping is controlled by an effusion cell. The ideal growth conditions for Nd incorporation maintaining crystal quality in GaN were investigated. The optical absorption characteristics indicate that the GaN:Nd epilayer remains transparent at the Nd emission wavelength of interest. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectrometry data indicate ˜5 at. % in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation up to ˜1 at. % Nd. The highest luminescence intensities correspond to a doping range 0.05-1 at. %, with the strongest emission occurring at 1.12 eV (1107 nm). We also present the Stark energy sublevels of Nd3+ ions in GaN as determined by luminescence spectra. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). We correlate the photoluminescence spectra with transitions from the 4F3/2 excited state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above (325nm) and below (836nm) bandgap excitation. Spectral correlation of the Nd emission multiplets in addition to site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site compared to other techniques (ion implantation and co-sputtering).

A simple preparation technique of ZnO thin film with high crystallinity and UV luminescence intensity

In this study, the Zn thin films were evaporated on the glass substrates at room temperature (RT). Then the substrates were transferred into a thermal tube furnace to form the ZnO thin films. This oxidation processes were carried out in the air by two steps: 250 °C for 2 h and then 400, 450, 500, 550 or 600 °C for another 1 h. The X-ray diffraction (XRD) and the scanning electron microscopy (SEM) studies indicate that the ZnO thin film obtained at 500 °C has the best crystallinity. The RT photoluminescence (PL) measurements also show that the film oxidized at 500 °C exhibits the highest ultraviolet (UV) emission intensity at 370 nm with the narrowest full-width at half-maximum (FWHM) of 110 meV. By optimizing the process parameters of this simple technique, high quality ZnO thin films can be acquired.

Luminescent Properties of Mn2+ in Hexagonal Aluminates under Ultraviolet and Vacuum Ultraviolet Excitation

Mn2+-doped xBaO center dot 6Al(2)O(3) and BaMgAl10O17 phosphors were prepared by solid-state reaction. The investigation of vacuum ultraviolet (VUV) excitation spectra of these phosphors exhibits that 0.82BaO center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ have a stronger absorption than BaO center dot 6Al(2)O(3):Mn2+ at about 147 nm. The emission spectra under VUV excitation demonstrated that 0.82BaOBa center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ have a higher luminescent intensity than BaO center dot 6Al(2)O(3):Mn2+. The lifetime analysis indicates that they have similar decay times, indicating that 0.82BaOBa center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ can be used as luminescent materials for plasma display panels. We observed that the critical concentration of the Mn2+ ions by host excitation is different from that of Mn2+ direct excitation, revealing a different mechanism of energy transfer. The critical distance was calculated. A model was suggested to explain the process of the energy transfer from the host to the Mn2+ ions.

Preparation of red phosphor (Y, Gd)BO3:Eu by soft chemistry methods

The three soft chemistry methods were employed to prepare the red phosphor (Y, Gd)BO3:Eu, such as coprecipitation–combustion method, salt assisted combustion method and emulsion method. The main factors affecting particle size, particle distribution and luminescent properties of the product were investigated in detail, and as a result, the preparation processes were optimized. The phosphors were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electronic microscope (TEM) and vacuum ultraviolet (VUV) spectra. Results reveal that phosphors with different morphology, small particle size and high luminescence intensity could be obtained by soft chemistry methods. The difference between the luminescence properties of phosphors in this work and commercial rare earth borate phosphor is discussed. The phosphor with grain shape and high luminescence intensity could be prepared by coprecipitation–combustion method, nanophosphor could be prepared by salt assisted combustion method, and spherical phosphor with a narrow size distribution could be obtained by using emulsion method.

Luminescent characteristics and microstructures of Sr2CeO4 phosphors prepared via sol–gel and solid-state reaction routes

Blue-light-emitting Sr2CeO4 phosphors were synthesized via a sol–gel process and the conventional solid-state method in this study. The developed sol–gel process lowered the synthesis temperature of monophasic Sr2CeO4 to as low as 900 °C. In comparison with the solid-state derived powders, the sol–gel derived powders had more uniform morphology and smaller particle sizes. In addition, sol–gel derived Sr2CeO4 displayed higher luminescent intensity than that prepared via the solid-state route under the same heating conditions. This is attributed to the improved compositional homogeneity and crystallinity in the sol–gel process. During the heating processes, Sr2CeO4 tended to thermally decompose at elevated temperatures. This decomposition reaction resulted in the formation of an impurity phase- SrCeO3 and thereby a decrease in the luminescent intensity. For obtaining Sr2CeO4 phosphors with high luminescent intensity, the heating conditions in both processes need to be well modulated.

Synthesis and Characterization of Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;:Eu&lt;sup&gt;3+&lt;/sup&gt; Film Derived by Sol-Gel Processing

Y2O3:Eu3+ thin film was synthesized by sol-gel method with inorganic salt raw materials, and the crystal structure and luminescent properties were investigated. By adding organic additive to the sol, a homogeneous film with high luminescent intensity could be obtained by dip-coating technique on the surface of alumina sheet and quartz glass. Structures of the films were studied by XRD and SEM. The excitation spectra of the films showed a wide excitation peak from 200nm to 260nm, and the emission spectra had a strongest emission peak at 611nm which revealed a close relationship with the calcining temperature.

Luminescence Properties of MO-Re2O3-B2O3:Eu3+ (M= Mg, Sr; Re=Y, Gd ) under VUV Excitation

The phosphors of MO-Re2O3-B2O3:Eu3+ (M = Mg, Sr; Re = Y, Gd) were prepared by conventional solid-state reaction. Red-emitting MO-Re2O3-B2O3:Eu3+ (M=Mg, Sr; Re=Y, Gd) phosphors had the highest luminescence intensity under vacuum ultraviolet (VUV) excitation. They had sharp emission peak lines at 591 and 613nm, which were assigned to the transitions of 5D0→7F1 and 5D0→7F2. By the introduction of Sr into MgO-Re2O3-B2O3:Eu3+ (M=Mg, Sr; Re=Y, Gd), the intensity of absorption peaked at 172nm and the emission peak intensity were enhanced.