Orange-red Band Research Articles

A single-phase white-emitting Ca2SrAl2O6:Ce3+,Li+,Mn2+phosphor with energy transfer for UV-excited WLEDs

A series of Ca2SrAl2O6:Ce(3+),Li(+),Mn(2+) phosphors have been synthesized by traditional solid state reactions. The structure and photoluminescence properties of the samples together with the energy transfer from Ce(3+) to Mn(2+) ions have been investigated in detail. The obtained phosphors can be excited efficiently by UV excitation and exhibit a broad blue-green emission band peaking at 470 nm and an orange-red emission band at 610 nm, which result from the f-d transition of the Ce(3+) and the (4)T1-(6)A1 transition of the Mn(2+) ions, respectively. By varying the doping concentration of the Mn(2+) ion, a series of tunable colors including white are obtained at an irradiation of 355 nm. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis of photoluminescence spectra and decay curves of the phosphors. The critical distance between the Ce(3+) and Mn(2+) ions has been calculated by both the concentration quenching method and the spectral overlap method. Preliminary studies on the properties of the phosphor indicated that our prepared Ca2SrAl2O6:Ce(3+),Li(+),Mn(2+) phosphor might have potential application as a single-phase white-emitting phosphor for WLEDs.

Structure, photoluminescent and cathodoluminescent properties of a rare-earth free red emitting β-Zn3B2O6:Mn2+phosphor

A rare-earth free red emitting β-Zn3B2O6:Mn(2+) phosphor was prepared by a solid-state reaction method. The crystal structure, photoluminescent and cathodoluminescent properties of β-Zn3B2O6:Mn(2+) were systematically investigated. The absorption and photoluminescence excitation spectra confirm that β-Zn3B2O6:Mn(2+) matches the UV LED chip. Under UV light and low-voltage electron beam excitations, an interesting orange-red emission band centered at ∼600 nm of Mn(2+) at the tetrahedral Zn(2+) sites is observed. Besides, the unusual red shift with increasing Mn(2+) content is also found and contributed to an exchange interaction between Mn(2+). In addition, under low-voltage excitation, β-Zn3B2O6:Mn(2+) exhibits higher color purity of 98.1% than that of the commercial ZnS:Ag,Cd yellow phosphor and reported ZnGeN2:Mn(2+) orange phosphor, which indicated the β-Zn3B2O6:Mn(2+) has a patenting application in FEDs.

A complex study of the fast blue luminescence of oxidized silicon nanocrystals: the role of the core

Silicon nanocrystals (SiNCs) smaller than 5 nm are a material with strong visible photoluminescence (PL). However, the physical origin of the PL, which, in the case of oxide-passivated SiNCs, is typically composed of a slow-decaying red-orange band (S-band) and of a fast-decaying blue-green band (F-band), is still not fully understood. Here we present a physical interpretation of the F-band origin based on the results of an experimental study, in which we combine temperature (4-296 K), temporally (picosecond resolution) and spectrally resolved luminescence spectroscopy of free-standing oxide-passivated SiNCs. Our complex study shows that the F-band red-shifts only by 35 meV with increasing temperature, which is almost 6 times less than the red-shift of the S-band in a similar temperature range. In addition, the F-band characteristic decay time obtained from a stretched-exponential fit decreases only slightly with increasing temperature. These data strongly suggest that the F-band arises from the core-related quasi-direct radiative recombination governed by slowly thermalizing photoholes.

Preparation and properties of rare earth luminous fiber containing red organic fluorescent pigment

Rare earth luminous fiber was prepared by method of melt spinning. X-ray diffraction (XRD), scanning electron microscopy (SEM), and fluorescence spectrophotometer as well as afterglow brightness tester were used to characterize the resulting samples. Results from XRD and SEM demonstrated that the phase of SrA12O4:Eu2+, Dy3+ in the fiber was not destroyed in the manufacturing process and the as-formed luminous fiber consisted of irregular particles. Under ultraviolet excitation, the luminous fiber exhibited a yellow-green and orange-red emission band with a maximum at 520 nm and around 600 nm originating from SrAl2O4:Eu2+, Dy3+ and red organic fluorescent pigments. The energy transfer process was further studied. Furthermore, the emission colors of luminous fibers could be tuned from yellow-green to orange-red easily by doping red organic fluorescent pigment, making the materials have potential application in many areas.

Synthesis and characterization of novel K2La2−xEuxTi3O10 phosphor for blue chip white LEDs

Eu3+ doped K2La2Ti3O10 (KLT) phosphors were prepared by means of conventional solid state reaction method. It has exhibited an intense excitation band at around 466nm, which matches well to the popular emission line from a GaN based blue light-emitting diode (LED) chip. Using this as an excitation wavelength the Eu3+ doped KLT phosphors yielded two strong orange-red emission bands at 595nm (5D0→7F1) and 616nm (5D0→7F2) respectively. The obtained results suggest that Eu3+doped KLT phosphors are useful for blue chip white LEDs. Besides we have studied its dielectric properties along with the other significant characterizations like XRD, SEM and Tg-DTA.

Solvothermal Synthesis and Luminescence Properties of BaCeF5, and BaCeF5: Tb3+, Sm3+ Nanocrystals: An Approach for White Light Emission

Novel monodisperse BaCeF5 and BaCeF5: Tb3+, Sm3+ nanocrystals have been successfully synthesized by a simple one-step solvothermal synthesis. Uniformly distributed nanocrystals with an octahedral morphology and particle size of 75-80 nm were observed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photo-luminescence (PL), and decay studies were employed to characterize the samples. Under ultraviolet irradiation, the BaCeF5: Tb3+, Sm3+ samples exhibit the typical green emission band of the Tb3+ ions, as well as an orange-red and red emission bands of the Sm3+ ions in the presence of Ce3+ ions. The highly intense orange-red and red emission bands of the Sm3+ ions were attributed to the effective energy transfer from the Tb3+ to Sm3+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of BaCeF5: Tb3+, Sm3+ nanophosphors can be easily tuned by changing the concentration of Sm3+ ions. These results suggest that BaCeF5: Tb3+, Sm3+ nanocrystals can be explored for three-dimensional displays, back lighting, white light sources, and so on.

Tin-Doped Rutile Titanium Dioxide Nanowires: Luminescence, Gas Sensor, and Field Emission Properties

Sn-doped rutile TiO2 nanowires were synthesized by a thermal reactive evaporation route. Field emission scanning electron microscopy (FESEM) imaging reveals that the Sn-doped TiO2 nanowires exhibited diameters of 80-150 nm and 2-3 microns in length. High-resolution transmission electron microscopy (HRTEM) imaging makes it possible to observe that Sn-doped TiO2 nanowires show a certain lattices fringe of approximately 0.32 nm, which demonstrates that the nanowires are single crystalline with rutile structure and grow along the [110] axis. Cathodoluminescence (CL) reflected that on the surface of Sn-doped TiO2 nanowires, many oxygen vacancies and defect states were formed during the crystal growth. These defect states raised a broad emission peak around the red-orange band. The ethanol sensing properties of Sn-doped rutile TiO2 nanowires at a temperature of 190 degrees C for the ethanol concentrations of 50, 100, 150, 200, 400, 500, and 600 ppm, correspond to the sensor' sensitivity of 7, 12, 18, 19, 23, and 26%, respectively. The sensitivity increased with an increase in the ethanol concentration. As-synthesized TiO2 nanowires revealed a turn-on field, approximately 5.1 V/microm, at a current density of 1 microAcm(-2).

Plant lighting system with five wavelength-band light-emitting diodes providing photon flux density and mixing ratio control

BackgroundPlant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED) technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses.ResultsWe have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD). The average photosynthetic PFD (PPFD) in the irradiated area was 438 micro-mol m–2 s–1 (coefficient of variation 9.6%), which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD) of 1 micro-mol m–2 s–1 nm–1 at every peak wavelength (405, 460, 630, 660, and 735 nm) grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength), the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg) and the blue-light SPFD gradient (micro-mol m–2 s–1 nm–1 m–1) was 2 deg per 1 micro-mol m–2 s–1 nm–1 m–1.ConclusionsThe plant lighting system, with a computer with a graphical user interface program, can control the PFD and mixing ratios of five wavelength-band lights. A highly uniform PFD distribution was achieved, although an intentionally distorted PFD gradient was also created. Phototropic responses of oat coleoptiles to the blue light gradient demonstrated the merit of fine controllability of this plant lighting system.

Synthesis and photoluminescence of AlN:Mn hexagonal maze-like complex nanostructure

The AlN:Mn hexagonal maze-like complex nanostructure was prepared via a simple thermal chemical vapor deposition process without structure-directing templates or catalysts. The optical property of the product was investigated by room-temperature photoluminescence (PL) measurement. Two emission bands centered at 490nm and 600nm, respectively. In addition to a familiar red-orange band centered at 600nm originating from intra 3d-electrons transition of Mn2+ ion, another strong broad blue-green band around 490nm is related to VAl3−−3×ON+ defect complexes. The results indicate that the AlN:Mn maze-like complex nanostructure has a certain amount of Al vacancies, and the growth mechanism can be ascribed to nucleus arrangement and preferential growth.

Effect of annealing on the structural and luminescent properties of ZnO nanorod arrays grown at low temperature

Vertically well-aligned ZnO nanorod arrays were synthesized on glass substrates by a two-step chemical bath deposition method. The structural and luminescent properties of as-grown and air annealed samples were investigated. Scanning electron microscopy, x-ray diffraction and Raman spectra demonstrate that ZnO nanorods are well oriented with c-axis perpendicular to the substrates. Photoluminescence spectra show a weak ultraviolet emission and an intense broad visible emission band for as-grown and air annealed samples. These visible emission bands exhibit dependences of post annealing temperatures and excitation energies: (1) as the annealing temperature increases, the visible emission band gradually red-shifts from yellow to orange-red; (2) the optimal excitation energy for yellow and orange-red emission band is near the band-gap energy; (3) green emission band can be excited only by the energies lower than the band-gap energy and this emission becomes weak after high temperature annealing. A depletion region model is presented to explain the origins and red-shift of the visible emission bands. The recombination of a delocalized electron in the interstitial zinc close to the conduction band with a deeply trapped hole in the single negatively charged interstitial oxygen center in the deletion region (in the bulk) is responsible for the yellow (orange-red) emission.

Photoluminescence properties of silica aerogel/porous silicon nanocomposites

The luminescent properties of nanocomposite pellets based on silica aerogel and porous Si powder are studied depending on the ratio of chemical compounds. The photoluminescence of nanocomposites is characterized by a red–orange band related to silicon nanoparticles and a blue–green band related to silica aerogel with close values of decay time and activation energy. Remarkable tuning of nanocomposites' photoluminescence spectra in the RGB region is established allowing their use as promising phosphor materials for light-emitting diodes. The outgoing spectra of pellet photoluminescence are guided by the chemical composition ratio, porous Si and silica aerogel technology, and the storage time in ambient atmosphere. It was shown that using the silica aerogel as a dielectric matrix considerably increases the stability of photoluminescence yield of silicon nanoparticles.

Multiband Orange-Red-Emitting Phosphors SrY3SiP5O20 : Eu3 + under Near-UV Irradiation

The photoluminescence properties of silicon-based xenotime-type rare-earth phosphate as an orange-red-emitting phosphor material, (0.2, 0.6, 1, 2, 3, 5, 10, and 15 mol %), are reported. The photoluminescence spectra of the silicon phosphate indicated the simultaneous occurrence of six predominant orange-red band emissions due to doubly split magnetic-dipole , electric-dipole , and unusual transitions under a near-UV wavelength excitation. The multiband emission of at is attributed to the odd-parity distortions of the surrounding environment. With high concentration, the phosphor has a strong excitation due to f–f transitions appearing at around 396 nm, which correspond to the popular emission line from a near-UV light-emitting diode (LED) chip. Thus, the intense orange-red emission of the silicon phosphate phosphors under near-UV excitation suggests them to be a potential candidate for white light generation by using near-UV LEDs.

Ferromagnetic properties of Mn-doped AlN

Mn-doped AlN polycrystalline powders with a wurtzite structure were synthesized by solid-state reactions. A red-orange band at 600 nm, due to Mn 3+ incorporated into the AlN lattice, is observed in the photoluminescence (PL) spectrum at room temperature (RT). Magnetic measurements show the samples possess hysteresis loops up to 300 K, indicating that the obtained powders are ferromagnetic at around RT. The Mn concentration-induced RT ferromagnetism is less than 1 at%. Our results confirm that the RT ferromagnetism can be realized in Mn-doped AlN.

Jahnsite-(NaFeMg), a new mineral from the Tip Top mine, Custer County, South Dakota: Description and crystal structure

Jahnsite-(NaFeMg), NaFe 3+ Mg 2 Fe 2 3+ (PO 4 ) 4 (OH) 2 ·8H 2 O, space group P 2/ a , a = 15.0811(16), b = 7.1403(8), c = 9.8299(11) A, β = 110.445(1)°, V = 991.8(2) A 3 , and Z = 2, is a new mineral from the Tip Top mine, Custer County, South Dakota. It occurs as the dominant chemical zone in transparent pseudo-orthorhombic twinned prisms up to 1 mm long with shallow wedge-like terminations, both as isolated twinned crystals and in subparallel to divergent intergrowths. The crystals are yellow with orange-red bands just below the terminations. The mineral has a white streak, vitreous luster, Mohs hardness of 4, and good {001} cleavage. The measured density is 2.58(2) g/cm 3 , and the calculated density is 2.608 g/cm 3 . It is optically biaxial (–), with α = 1.632(1), β = 1.669(1), γ = 1.671(1) (589 nm); 2 V (meas.) = 25(5)°, 2 V (calc.) = 26°; dispersion: r > v , very strong; orientation: Y = b , Z ^ a = +28° (in β obtuse); pleochroism: X = colorless, Y and Z = beige; Y = Z > X . Electron microprobe analyses provided: Na 2 O 2.82, CaO 0.34, MnO 0.32, MgO 10.27, Fe 2 O 3 27.35, P 2 O 5 35.93, H 2 O 21.58 (calc.), total 98.61, which in terms of the general formula for the whiteite-jahnsite group XM1M2 2 M3 2 (PO 4 ) 4 (OH) 2 ·8H 2 O, yields the empirical formula: (Na 0.72 Ca 0.05 Mn 0.04 2+ )(Fe 0.72 3+ Mg 0.01 )Mg 2.00 Fe 2.00 3+ (PO 3.77 OH 0.23 ) 4 (OH) 2 ·8H 2 O. Crystal structure refinement ( R 1 = 0.041) supports these cation site assignments. Typical crystals have as many as five chemical zones from base to termination corresponding to the following jahnsite species: jahnsite-(NaMnMg), jahnsite-(NaFeMg), jahnsite-(CaMnMg), jahnsite-(NaFeMg), jahnsite-(CaMgMg). The characterization of the new mineral jahnsite-(NaFeMg) is based upon the second zone listed, which corresponds to roughly 80% of the crystal volume. Jahnsite-(NaMnMg) and jahnsite-(CaMgMg) also represent new species; however, the very small volume of these zones is insufficient to permit complete characterization of these species. Jahnsite-(NaFeMg) is the first member of the whiteite-jahnsite group in which a monovalent cation (Na + ) predominantly occupies the X site and a trivalent cation (Fe 3+ ) the M1 site. The structure differs from that determined for jahnsite-(CaMnMg) in that the X site is [8]-coordinated and the M1 and P1 polyhedra exhibit greater distortions caused by cation-cation repulsion across their shared edges. The determination of H positions allows the elucidation of a definitive H-bonding scheme.

A Study on Fabrication, Morphological and Optical Properties of Lead Sulfide Nanocrystals

To investigate the properties of lead sulfide (PbS) nanocrystals, we have prepared PbS nanocrystals on/in the porous alumina membrane with a pore diameter 20 nm. Utilizing the reaction of Pb wires and the hydrogen sulfide (H2S) gas, PbS nanocrystals produced and grew as the reaction time increased. The composition identification of the nanocrystals was performed by the XPS and EDS analyses. More structure characteristics of the PbS nanocrystals obtained from the TEM analysis. As indicated in the PL spectra, an orange-red emission band appeared and the emission intensities were obviously related to the defects in the nanocrytals. A significant quantum confinement effect made the energy gap of PbS nanocrystals produce a blue shift from 0.41 eV to 1.89 eV. Furthermore, the growth mechanism of the PbS nanocrystals was also discussed.

Mn, Cu Doping and Optical Properties of Highly Crystalline Ultralong ZnS Nanowires

Manganese (Mn) and copper (Cu) doping of ZnS nanowires was achieved by thermal evaporation of Mn, Cu doped ZnS nanopowders. Field emission scanning electron microscopy, and X-ray diffraction studies of the obtained ZnS nanowires demonstrate that the nanowires are single crystal structures and have diameters about 30-200 nm and lengths up to 1 millimeter. Room temperature photoluminescence (PL) measurements show a common PL peak around 520 nm for all ZnS nanowires samples, while impurity-related emission band are observed in doped ZnS nanowires. The dependence of the PL intensity on Mn doping concentration has also been investigated. It is shown that for high Mn doping concentration (10%) in the starting ZnS nanopowders, new emission bands (orange-red and red bands) are observed from the ZnS:Mn nanowires products. The origins of these new emission bands are discussed and brought up for further discussion.

Novel Class of Aeschynite Structure LaNbTiO6-Based Orange-Red Phosphors via a Modified Combustion Approach

A novel class of orange-red phosphors based on Eu(3+)-activated LaNbTiO(6) was successfully fabricated by a wet chemical method, called a modified combustion approach. XRD, TG-DTA, SEM, and EDS results show that the heat-treatment of the powders above 1000 degrees C is enough to obtain highly crystallized and phase-pure LaNbTiO(6) and Eu(3+)-doped samples, which is of prime importance in investigating the optical properties of the novel phosphors using LaNbTiO(6) as the host material. UV-vis diffuse reflectance spectroscopy reveals that the direct band gap of LaNbTiO(6) with large grains (above 200 nm) is calculated to be 3.27 eV, while the absorption edge of the small particles shows an obvious blue-shift. Two blue emission bands centered at 440 and 470 nm ascribed to the self-trapped exciton emission of the distorted NbO(6) and TiO(6) groups for the pure LaNbTiO(6) can be obtained. Photoluminescence spectra of the Eu(3+)-doped phosphor particles illuminated the simultaneous occurrence of several intense orange-red band emissions due to the characteristic transitions of (5)D(0,1) --> (7)F(J) (J = 0, 1, 2, 3, 4) of Eu(3+) under 395 nm excitation. The mechanism of these multiplets possibly arising from the odd-parity distortions of the Eu(3+) ion environment and the effect of crystallanity of the compounds on luminescence were discussed, respectively. The highly bright and color-uniform fluorescence images of the doped samples with short luminescence decay times (nanosecond magnitude) confirmed the potential applications of the phosphors in luminescence and display devices.

Infrared and Photoluminescence Study of Rapidly Thermally Annealed SiO<sub>x</sub> Thin Films

Silicon suboxide, SiOx thin films with different oxygen contents (1.15≤x≤1.70) were prepared by thermal evaporation of silicon monoxide at a residual oxygen pressure of 1·10-3 Pa and deposition rates of 0.2, 1.0, 3.0 and 6.0 nm/s. Rapid thermal annealing (RTA) of films was carried out at 1100°C in vacuum for 15 and 30 s and the films were analyzed by infrared (FTIR) and photoluminescence (PL) spectroscopy. In the FTIR spectra of SiOx annealed samples, a blue-shift of the stretching band with initial oxygen content, x, is observed. This band is shifted to a much lower frequency with prolonged RTA time. This behavior can be interpreted in terms of the partial decrease of oxygen content and film density upon annealing in vacuum. With annealing time increase a new band at 1106 cm-1 appears. Therefore, infrared spectra of SiOx films are significantly affected by the oxygen content. PL spectra of these films also change drastically with increasing annealing time. In the PL spectra of films annealed for 15 s two bands are easily visible: broad redorange band at 2.2 eV and a green band at 2.4 eV, while for 30 s annealing only low-energy band exists. Green band is connected with the defects in the SiOx matrix while red-orange band can be deconvoluted into several bands at 2.0, 2.3 and 2.5 eV. Two types of defects can be responsible for the PL band at about 2 eV: defects in a-Si (amorphous silicon) nanoparticles separated during RTA, and nonbridging oxygen hole recombination centers (NBOHC) formed by loosing of oxygen during RTA. The PL band at 2.3 eV is associated with the defects formed at a-Si/SiOx interfaces while a hardly visible band at 2.5 eV is related to the defects connected with the oxygen deficiency formed in the SiOx matrix during RTA.

Photophysics and Bonding in Neutral Gold(I) Organometallic Complexes with an Extended Aurophilic Supramolecular Structure

This work represents a synergistic experimental/computational study of the molecular spectroscopy and bonding in Au(CO)Cl in solution and the solid state. The luminescence behavior for crystalline solids is similar for Au(CO)Cl and related (RNC)AuCl complexes that likewise stack in infinite chains, and both exhibit orange-red unstructured phosphorescence bands with extremely large Stokes shifts ((15−20) × 103 cm-1). The long aurophilic distances computed for the ground state (∼3.2 Å) are contracted in the phosphorescent excited state (∼2.6 Å), demonstrating excimeric Au−Au covalent bonds. The spectral data suggest phosphorescent species in which the excimeric Au−Au bonding is extended beyond two adjacent molecules in the solid state. Controlling the concentration in frozen solutions attains phosphorescent bands due to dimeric species for which the emission energies are higher (in the blue region) than those for crystalline solids and are reproduced by ab initio calculations. The spectral findings herein suggest that predictive information about the supramolecular structure may be obtained by the luminescnce behavior. This is exemplified by crystals of (1,1,3,3-Me4BuNC)AuCl, whose red-orange luminsecence anticipated an extended-chain supramolecular structure, which was later verified crystallographically, as the molecules were found to pack in zigzag chains with alternating short (3.418 Å) and long (4.433 Å) aurophilic distances. Solutions of Au(CO)Cl exhibit negative deviation from Beer's law for, higher-energy monomer bands with the appearance of lower-energy bands at high concentrations due to the dimerization of molecules. Time-dependent density-functional theory (TD-DFT) calculations for monomer and dimer models show good agreement with the experimental spectra and account for the major absorption bands. Ab initio calculations (CCSD(T)/cc-pVTZ) show a blue shift of ∼23 cm-1 in the νC⋮O frequency upon complexation, thus providing the first computational evidence of this anomalous blue shift known experimentally for Au(CO)Cl.

Preparation of ( Sr1 − xCax ) 2Si5N8 ∕ Eu2 + Solid Solutions and Their Luminescence Properties

A series of ternary nitride solid solutions with a general formula of (2 atom %) were synthesized by the carbothermal reduction and nitridation (CRN) method. The structure and luminescence properties were characterized for practical applications as a potential red phosphor for the phosphor-converted white light-emitting diodes (LEDs). The solid solutions were formed as the uniformly single phases with orthorhombic and monoclinic (Cc) symmetry at each end of , while in the range of , such solid solution phases coexisted. All of the obtained phosphors were well crystallized and the grains grew from with increasing content. These phosphors showed broadened excitation spectra originated from the transition of ions, so that the intense orange-red emission bands were observed under the excitation of corresponding to the output lights of near-UV or blue LEDs.