Green Luminescence Band Research Articles

Effects of surface conditions on the visible luminescence of ZnO

The effects of surface conditions on photo-induced-carrier (PIC) diffusion are studied by solving one-dimensional continuity equation. Using various forms of ZnO samples with different surface conditions, the PICs lost at sample surface are substantiated to have important contributions to the visible luminescence. For unpassivated ZnO nanorods and single-crystal samples that undergo a high-temperature annealing in air, the visible luminescence originating from the PICs diffused to the surface is estimated more than 99.8 % and 70 % at room temperature, respectively, and more than 99.99 % and 97 % at low temperature. The structureless luminescence caused by PICs, such as the green, yellow, and orange luminescence bands are well fitted under the framework of tail-state luminescence, while the structured green band is suggested to be in association with a specific type of surface states formed during high-temperature annealing in oxidizing atmosphere and can be fitted with Huang-Rhys model by taking into account tail-state luminescence.

Synthesis and characterization of MgZnCo ternary mixed metal oxide by the sonochemical method for solid hydrogen storage

In the present investigation, MgZnCo ternary nanocomposites were developed via a one-step sonochemical technique. The nanocomposite was characterized using structural and optical methods. The formation of different crystalline nanocomposite phases (MgO, ZnO, and Co3O4), and a binary phase (Mg-Zn) has been confirmed by X-ray diffraction. Also, it was indicated that varying of Co molar ratio had an impact on the average sizes of the nanoparticles. SEM showed octahedron-shaped nanoparticle morphology with different average sizes for the nanocomposites prepared. Photoluminescence analysis showed the presence of green and ultraviolet emissions, with green luminescence bands being most often observed. with the intention of discovering samples with suitable structural and optical properties for future solid hydrogen storage applications.

Sonochemical synthesis and characterization of new nanostructured ternary composites based on Mg, Zn, and Co

A simple and rapid method for synthesizing new ternary nanocomposites based on Mg, Zn, and Co has been developed using ultrasound technology. The nanocomposites were characterized using structural, optical, and thermal methods. XRD diffraction confirmed the formation of different crystalline nanocomposite phases (MgO, ZnO, and Co3O4) and binary phase (Mg–Zn), while Raman spectroscopy and FTIR, identified the vibration modes and provided information on functional groups and chemical bands present in samples. SEM showed the octahedron-shaped nanoparticles morphology with different averages size for the nanocomposites oxide prepared. Photoluminescence analysis showed the presence of green, blue, and ultraviolet emissions, with green luminescence bands being most often observed. Heat capacity and thermal diffusivity measurements were used to study thermal properties.

Photoluminescence from GaN Implanted with Be and F

GaN samples are implanted with Be and F and annealed in different conditions to activate the BeGa acceptors. Photoluminescence spectra are studied to recognize the defects. The UVLBe band with a maximum at 3.38 eV and the YLBe band with a maximum at 2.15 eV are observed and associated with Be. The sequential implantation of Be and F ions into GaN at 600 °C reduces the concentration of nitrogen vacancies (VN), as evidenced by the lack of the green luminescence band associated with the isolated nitrogen vacancy. First‐principles calculations are employed to find parameters of defects that can form after implantation.

LUMINESCENCE OF TWO-DIMENSIONAL ZnO NANOSTRUCTURES: NANOWALLS, NANOSHEETS, NANOCOMBS

Preliminary comparative studies of the photoluminescent properties of two-dimensional ZnO nanostructures with morphology of nanowalls, nanosheets, and nanocombs, fabricated by gas-transport synthesis, have been performed. All structures exhibited near-band-edge (NBE) UV emission of the same order of intensity. Unlike nanocombs, whose spectrum contains a comparatively strong green luminescence band, nanowalls and nanosheets are characterized by a large ratio of the UV and visible components. This distinction is presumably due to the difference in the mechanisms of structure formation: nanowalls and nanosheets are formed according to the vapor–liquid–solid mechanism, whereas nanocombs grow according to the vapor–solid mechanism

High contrast green luminescence from spin-coated Mo-doped β-Ga2O3 thin films

High-contrast green luminescence was obtained from molybdenum (Mo)-doped beta-phase gallium oxide (β-Ga2O3) by a sol-gel spin coating method. The X-ray diffraction, atomic force microscopy, and ultraviolet–visible–near infrared transmission results revealed that the Mo dopants did not significantly affect the fabricated films’ crystal structure, surface morphology, and energy bandgap (Eg). All spin-coated Mo-doped films formed a beta phase structure and exhibited smooth surface morphology with a root-mean-square surface roughness of less than 7 nm. The thickness of the coated film increased gradually with Mo doping concentration. In the photoluminescence measurements, a green luminescence band associated with the Mo ion dxz-dyz band transition slowly appeared, which hindered the original emission from the recombination of electron–hole pairs in β-Ga2O3 but increased overlapped green color luminescence. Compared with the undoped β-Ga2O3, the CIE chromaticity diagram showed that luminescence changed from blue to green, and the contrast of the green luminescence significantly improved from 0.33 to 0.73.

Cool white light and tunable multicolor emission from Tb3+/Dy3+ co-activated glasses under different excitations for WLEDs

A set of co-doped (Tb3+/Dy3+) lithium zinc borate (LZB) glasses were developed by melt quenching. The structural evaluation was performed for synthesized glassy matrices. The Dy3+ and Tb3+ individually doped glasses exhibit intense yellow and green luminescence bands at 575 nm (4F9/2 → 6H13/2) and 543 nm (5D4→7F5), respectively. The sensitization effect of Dy3+ on Tb3+ was analyzed by increasing the Tb3+ content with respect to the optimum Dy3+ content (0.5 mol%) in Dy3+/Tb3+. The spectral overlay of Dy3+ luminescence and Tb3+ absorption profiles, Dy3+/Tb3+ PL spectra under different excitations 352, 362, 376, and 385 nm, shortening decay lifetimes of Dy3+ in Dy3+/Tb3+ co-activated glasses, energy transfer (ET) parameters, chromaticity coordinates and their corresponding correlated temperatures all help to explain ET from Dy3+ to Tb3+. At 385 nm of Dy3+ excitation, the optimized co-activated (0.5Dy3++1.0Tb3+):LZB glass displays cool white light emission. The non-radiative ET from Dy3+ to Tb3+ is dominated by electric dipole–dipole interaction and its ET efficiency was calculated to be 63%. At the same time, reverse ET from Tb3+ to Dy3+ was also analyzed. The shift in color coordinates from dominant yellow to greenish-yellow, green and white light emission suggests that Dy3+/Tb3+ co-activated LZB glasses can be a potential candidate for UV converted multicolor and white light emitting devices.

Structured green luminescence band of ZnO nanorods —— the optical emissions coming from the sample surface

The optical emissions of O-annealed ZnO nanorods (ZnO NRs) before and after surface passivation are studied at temperatures of 295 to 17 K in terms of photoluminescence (PL) spectra, PL excitation spectra, and PL quantum efficiency. Because the ZnO NR samples maintain the surface free of mechanical damages during the sample preparation, unambiguous evidence is obtained to substantiate that the structured green luminescence (GL-S) bands come from the optical emissions on the sample surfaces. We suggest that the GL-S bands are excited by the excitons diffused to the sample surface and thus substantially reduced in the PL spectra of ZnO NRs after surface passivation. PL fitting shows that many kinds of surface states may have contributions to the optical emissions in the GL-S bands, leading to the variation of GL-S bands with annealing temperature and ambient environment.

Photoluminescence related to Ca in GaN

The ${\mathrm{Ca}}_{\mathrm{Ga}}$ acceptor in GaN was studied using photoluminescence (PL) experiments and first-principles calculations. The experimentally found $\text{--}/0$ transition level of the ${\mathrm{Ca}}_{\mathrm{Ga}}$ at 0.50 \ifmmode\pm\else\textpm\fi{} 0.02 eV above the valence band reasonably agrees with the value calculated using the Heyd-Scuseria-Ernzerhof functional tuned to fulfill the generalized Koopmans condition (0.70 eV). The ${\mathrm{Ca}}_{\mathrm{Ga}}$ acceptor is responsible for the green luminescence band (labeled ${\mathrm{GL}}_{\mathrm{Ca}}$) with a maximum at 2.5 eV. The electron- and hole-capture coefficients for the ${\mathrm{Ca}}_{\mathrm{Ga}}$ acceptor are obtained from PL experiments: ${C}_{n}=9\ifmmode\times\else\texttimes\fi{}{10}^{\text{--}14}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}/\mathrm{s}$ and ${C}_{p}=6\ifmmode\times\else\texttimes\fi{}{10}^{\text{--}7}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}/\mathrm{s}$. The ${\mathrm{GL}}_{\mathrm{Ca}}$ band is an efficient radiative recombination channel in GaN samples implanted with Ca and in unintentionally doped GaN grown by molecular-beam epitaxy at relatively low temperatures, where Ca is a common contaminant.

P-type conductivity and suppression of green luminescence in Mg/N co-implanted GaN by gyrotron microwave annealing

Co-implantation of Mg with N has been shown to improve p-type conductivity in Mg-implanted GaN. Achievement of p-type material still requires temperatures beyond the thermodynamic stability of GaN, however. In this study, we present results of implantation and anneal activation of GaN, co-implanted with Mg and N or Mg only by repeated, short thermal cycles of 1350 °C using a high-power gyrotron microwave source with a quasi-gaussian intensity profile. Spatial variations in optical and electrical properties of the resulting films are characterized by photoluminescence and diode I–V and C–V measurements. Resistive Mg/N co-implanted and annealed material shows dominant luminescence of the VN-related green luminescence (GL2) band at 2.37 eV and relatively lower intensity acceptor-related ultraviolet luminescence (UVL) at 3.27 eV. However, a material showing p–n diode behavior shows higher-intensity UVL luminescence and suppression of the GL2 band, permitting observation of the yellow luminescence (YL) present in the as-grown GaN. The YL is attributed to unintentionally introduced CN–ON complexes and is commonly observed in GaN grown by metalorganic chemical vapor deposition but is typically absent in implanted/annealed GaN. Co-implanted material is compared to material implanted only with Mg and annealed under the same conditions, which shows p-type activation, but contains persistent GL2 luminescence post-anneal and lowers maximum hole concentration.

Effects of Surface States on the Green Luminescence in ZnO

The origin of green luminescence (GL) band is an issue long‐term pending in the research of ZnO. Herein, three GL bands (GL1, GL2, and GL‐S bands) are unambiguously identified using the single‐crystal samples with and without a SiOx passivation layer and the polycrystal samples annealed in H2 and O2 atmospheres. Solid evidence demonstrates that the GL1 band can be assigned to the optical emissions from the sample inside and the intensity is decreased with the decrease in temperature. The GL2 and GL‐S bands, which correspond to the structureless and structured GL bands of H‐ and O‐annealed samples, respectively, are found to come from the sample surface and enhanced at low temperatures. Excitons or free electrons and holes generated through interband absorption are found to play an important role in exciting both the GL2 and GL‐S bands. For the light with photon energy lower than the bandgap, however, the GL‐S and GL2 bands exhibit different excitation behaviors. The deficiency of oxygen on the sample surface is confirmed to be the reason resulting in the GL2 band and probably also the reason leading to the GL‐S band.

A photoactive iridium(III) complex with 3-methyl-2-phenyl pyridine and 1,1-bis(diphenylphosphino)methane: Synthesis, structural characterization and cytotoxicity in breast cancer cells

A photoactive complex [Ir(3m-ppy)2(dppm)Cl] (1; dppm = bis(diphenylphosphino)methane, 3 m-Hppy = 3-methyl-2-phenylpyridine), which shows a green luminescence band at 517 nm in DMSO was synthesized from reaction of the dimeric [Ir2(3m-ppy)4Cl2] with dppm under an inert atmosphere. Complex 1 was characterized by 1H NMR, FT-IR, ESI-MS spectroscopies and CHN analysis. Single-crystal X-ray analysis of 1 revealed a distorted octahedral geometry comprising an IrIII center with monodentate dppm, bidentate-C,N 3 m-ppy and chlorido ligands. The electrochemistry of 1 was studied by cyclic voltammetry in 0.1 M NaClO4 in acetonitrile on a glassy carbon working electrode, displaying an oxidation peak of IrIII/IV at 1.2 V. Complex 1 showed anticancer activity against MDA-MB-231, MCF-7 and HCC1937 cell lines of human breast cancer; the respective cytotoxicity factors of 160, 32 and 25 were significantly greater than the cytotoxicity factors obtained with cisplatin.

Optical and Structural Properties of Manganese‐Doped Zinc Oxide Grown by Metal‐Organic Chemical Vapor Deposition

AbstractThis systematic study investigates the optical properties and process−structure−property relationships of Mn‐doped zinc oxide (ZnMnO) grown by metal‐organic chemical vapor deposition with varying Mn‐doping concentration and growth conditions. ZnMnO exhibits a good crystal quality oriented in the (002) direction and contains intermixtures of zinc oxide (ZnO)‐like and manganese oxide (MnxOy)‐like phases. The material exhibits a direct energy absorption band‐edge and a reduction in bandgap with Mn‐doping. Photoluminescence studies show that Mn‐doping can simultaneously tailor broad green band luminescence and ultraviolet edge emissions. Post‐growth air‐annealing results in broad MnxOy‐related photoluminescence emissions at 3.3–4.5 eV. A further reduction in the absorption band‐edge is also observed with annealing. Results indicate that luminescence wavelengths and intensities, and absorption band‐edge can be tuned with the Mn‐doping process. This paper promotes a thorough understanding of defect centers in ZnO with transition metal doping and their interrelation with optical characteristics. The work provides a solid foundation for the development of optoelectronic devices, such as light emitting diodes, solar cells, lasers, and photodetectors using ZnO‐based materials.

Sample-dependent excitation behavior of the structured green luminescence band in ZnO

The photoluminescence spectra excited by different wavelength light from ZnO samples with and without SiOx passivation demonstrated that the excitation behavior of structured green luminescence (GL-S) band is determined by the surface conditions or the morphological forms. The lowest energy of photons able to excite the GL-S band varied from 3.380 eV down to a value far below the zero phonon line of GL-S band, depending on the defect density in the region near to the sample surface. The imperfections like cracks, scratches, and voids etc. were found decisive for the effectiveness of SiOx passivation on the GL-S band, which is removable only for the samples with good surface conditions. In addition, the phonon energy in GL-S band was determined to be ~3 meV lower than that of longitudinal optical phonons and thus was associated with the surface optical mode. The evidence of a link between the GL-S band and the optical emissions on sample surface revealed that there is no necessity to connect the GL-S band with any specific defects in the inside of samples. This optical emission mechanism is not only helpful to settle the relevant issues of visible luminescence in the research of ZnO, but also important to the study of other phenomena related to photoexcitation.

Medium Energy Carbon and Nitrogen Ion Beam Induced Modifications in Charge Transport, Structural and Optical Properties of Ni/Pd/n-GaN Schottky Barrier Diodes.

The irradiation effects of carbon and nitrogen medium energy ions (MEI) on charge transport, structural and optical properties of Ni/Pd/n-GaN Schottky barrier diodes are reported. The devices are exposed to 600 keV C2+ and 650 keV N2+ ions in the fluence range of 1 × 1013 to 1 × 1015 ions cm−2. The SRIM/TRIM simulations provide quantitative estimations of damage created along the trajectories of ion beams in the device profile. The electrical parameters like Schottky barrier height, series resistance of the Ni/Pd/n-GaN Schottky barrier diodes decreases for a fluence of 1 × 1013 ions cm−2 and thereafter increases with an increase in fluence of 600 keV C2+ and 650 keV N2+ ions. The charge transport mechanism is influenced by various current transport mechanisms along with thermionic emission. Photoluminescence studies have demonstrated the presence of yellow luminescence in the pristine samples. It disappears at higher fluences due to the possible occupancy of Ga vacancies. The presence of the green luminescence band may be attributed to the dislocation caused by the combination of gallium vacancy clusters and impurities due to MEI irradiation. Furthermore, X-ray diffraction studies reveal that there is a decrease in the intensity and shift in the diffraction peaks towards the lower side of two thetas. The reductions in the intensity of C2+ ion irradiation is more when compared to N2+ ion irradiation, which may be attributed to change in the mean atomic scattering factor on a given site for light C2+ ion as compared to N2+ ion.

Influence of Zn doping on the morphology and luminescence of Ga2O3 low-dimensional nanostructures

Zn-doped Ga2O3 nanostructures were synthesized by thermal evaporation. SEM results show that there are plenty of nanorods in the samples. The EDS analysis of the samples demonstrate that the nanostructures are mainly composed of Ga and O elements, and a small amount of Zn element is also observed. The Raman spectra indicate that the samples still keep the monoclinic structure consistent with the pure Ga2O3 crystal structure. A broad-band blue-green luminescence centered around at 2.3 eV was observed at room temperature. The luminescence intensity of the PL spectra of the Zn-doped Ga2O3 nanostructures varied with the amount of Zn doping. Besides, the PL spectra of the Zn-doped Ga2O3 nanostructures have a red-shift compared to that of the pure Ga2O3 nanostructures. The analysis of the PL spectrum of Zn-doped Ga2O3 nanostructures with a mass ratio of Ga2O3 powder to zinc powder of 10:1 indicates that the broad-band blue-green luminescence of the Zn-doped Ga2O3 nanostructures is composed of one blue luminescence (2.8 eV, 450 nm) band, one green luminescence (2.3 eV, 533 nm) band, one yellow luminescence (2.1 eV, 592 nm) band, and one red luminescence (1.9 eV, 638 nm) band, respectively. Further, their luminescence mechanisms will be discussed.

Влияние температуры апконверсионных частиц NaYF4:Er,Yb на формирование люминесценции

The intensity of upconversion luminescence depends nonlinearly on the excitation intensity. The aim of this work is to study the effect of the temperature of NaYF4:Er,Yb upconversion particles on the dependence of the luminescence intensity on the excitation intensity. The synthesized particles were observed to have the shape of a hexagonal prism with a width of about 440 nm and a height of 445 nm. The upconversion luminescence spectra were obtained in the temperature range of 22–55° C with the excitation intensity in the range of 1.5–9.4 W/cm2. The obtained results show the green-band luminescence photons can be generated by means of two-step and three-step mechanisms: the contribution of these mechanisms depends on the temperature of the particles. As the temperature increases, the contribution of the three-stage mechanism of green luminescence excitation is enhanced.

Suppression of Green Luminescence of Mg‐Ion‐Implanted GaN by Subsequent Implantation of Fluorine Ions at High Temperature

Herein, gallium nitride (GaN) samples implanted with magnesium (Mg) and fluorine (F) ions are investigated by photoluminescence (PL) measurements. In low‐temperature PL measurements, the characteristic green luminescence (GL) band attributable to nitrogen vacancies (VN) is observed in Mg‐ion‐implanted GaN. As VN are likely to act as donors, suppressing their formation is essential to realizing p‐type conductivity. The energy required for a F impurity to replace VN in GaN and eventually form F on a N site decreases when the Fermi level approaches the valence band maximum, and therefore F is employed as a subsequent implantation element to compensate for VN. The GL band peak disappears upon implanting Mg and F ions at a high temperature and adjusting the F concentration to an appropriate value. This result suggests that VN generated by Mg ion implantation can be suppressed using an element with a lower formation energy than that of VN.

TEMPERATURE-DEPENDENT PHOTOLUMINESCENCE STUDY OF POROUS GAP

This paper reports on the temperature-dependent photoluminescence of porous GaP under the 532-nm excitation. Porous GaP formed by electrochemical anodization of (111)-oriented bulk material exhibits green emission at 550 nm (2.25 eV) and red emission at 770 nm (1.65 eV) at room temperature. In the temperature range from 25 K to 275 K intensity from the green emission gradually decreases when the temperature increases. Additionally, peak position of the green luminescence band shifts to lower energy with increasing temperature and the same the GaP band gap narrowing with temperature. This means a contribution of lattice vibrations.

Optical properties for the oxygen vacancies in β-Ga2O3 based on first-principles calculations

We present a comprehensive study based on first-principles calculations for three different oxygen vacancies with three different charge states (0, +1, +2) in β-Ga2O3. We adopt the well-known FNV correction scheme for the finite-size system and overcome the ‘band-edge’ problem by the hybrid functional (method purposed by Alkauskas). Since the luminescence band of β-Ga2O3 still remain debatable and mysterious, we put our emphases on the optical properties of the oxygen vacancies and we find a new green luminescence (GL) band through theoretical calculation and attribute it to one of the three oxygen vacancies. Besides, optical absorption for all oxygen vacancies have peaks in UV region.