Photoluminescence Excitation Intensity Research Articles

Effect of different BaO contents on the photoluminescence properties of the Eu2+-doped high thermal stability Sr3−xBaxMgSi2O8 phosphors

In this study, 0.015 Eu[Formula: see text]-doped Sr[Formula: see text]BaxMgSi2O8 ([Formula: see text], 0.3, 0.6, 0.9) were used as compositions to find the effect of BaO content on their photoluminescence excitation (PLE) and photoluminescence emission (PL) properties. They were sintered at 1400°C in a reduction atmosphere of 95% N[Formula: see text]% H2 to form blue phosphors. X-ray diffraction pattern and SEM observation were used to analyze their crystal properties, and a fluorescence spectrophotometer was used to analyze their PLE and PL properties. After conducting a thorough analysis, our research primarily encompasses four significant research themes. First, SEM observations revealed that synthesized Eu[Formula: see text]-doped Sr[Formula: see text]BaxMgSi2O8 phosphors exhibit the formation of whisker-like structures. Therefore, the whisker-like structures in all the Eu[Formula: see text]-doped Sr[Formula: see text]BaxMgSi2O8 phosphors were analyzed using the HRTEM and its equipped EDS to find how BaO content influenced both the quantity and fineness of these whiskers. Second, we examined the impact of BaO content on the PLE and PL emission intensities of the Eu[Formula: see text]-doped Sr[Formula: see text]BaxMgSi2O8 phosphors across a temperature range from room temperature to 210°C. This investigation aimed to uncover the effects of BaO content and temperature on the thermal stability of the Eu[Formula: see text]-doped Sr[Formula: see text]BaxMgSi2O8 phosphors. Lastly, our fourth important investigation involved reorganizing the PLE spectra of the Eu[Formula: see text]-doped Sr[Formula: see text]BaxMgSi2O8 phosphors with the energy band as the x-axis. The Gaussian fitting function was applied to analyze the excitation spectra and discern the influence of BaO content on the value of the Stokes shift.

Investigations of Photoluminescence Properties of CaxMg2-xSi2O6:yEu2+ (x = 0.5-1.25, y = 0.015-0.035) Phosphors.

Previously, there were almost no relevant studies on developing the optimal CaxMg2-xSi2O6:yEu2+ phosphor composition for its finest optical properties. This study employs two steps to determine the optimal composition for CaxMg2-xSi2O6:yEu2+ phosphors. First, CaMgSi2O6:yEu2+ (y = 0.015, 0.020, 0.025, 0.030, 0.035) was used as the primary composition of specimens synthesised in a reducing atmosphere of 95% N2 + 5% H2 to investigate the effect of Eu2+ ions on the photoluminescence properties of each variant. The emission intensities of the entire photoluminescence excitation (PLE) and photoluminescence (PL) emission spectra of the CaMgSi2O6:yEu2+ phosphors initially increased as the concentration of the Eu2+ ions increased, peaking at y = 0.025. The cause of the variations across the entire PLE and PL spectra of all five CaMgSi2O6:yEu2+ phosphors was investigated. Because the CaMgSi2O6:0.025Eu2+ phosphor had the highest PLE and PL emission intensities, in the next step, CaxMg2-xSi2O6:0.025Eu2+ (x = 0.5, 0.75, 1.0, 1.25) was used as the primary composition to investigate the effect on the photoluminescence properties when the CaO content varied. We also show that the Ca content has an apparent effect on the photoluminescence properties of CaxMg2-xSi2O6:0.025Eu2+ phosphors, and the optimal phosphor composition is Ca0.75Mg1.25Si2O6:0.025Eu2+ because it has the largest PLE and PL values. X-ray diffraction (XRD) analyses of CaxMg2-xSi2O6:0.025Eu2+ phosphors were performed to identify the factors responsible for this outcome.

Exploring the excitation spectrum behavior of Dy in CaWO4 for a new excited-state-based ratiometric thermometry

Exploring excited-state transition behavior is of great importance for understanding the optical characteristics of lanthanide ions, which may potentially develop new optical thermometry by the thermally affected excitation processes. In this work, we explore the detailed excitation transition behaviors of Dy3+ and propose a new thermometry strategy based on excited-state absorption intensity ratio (EIR) in Dy3+ doped CaWO4 phosphors. The optimal Dy3+ doping concentration in CaWO4:Dy phosphors was determined and its fine excitation transition lines from low-lying levels of 6HJ (J = 15/2, 13/2, 11/2, and 9/2) to the respective high-lying levels of Dy3+ ions were identified by well-resolving the photoluminescence excitation (PLE) spectra. By taking advantage of the opposite trends of temperature-dependent PLE intensities of Dy3+, a new ratiometric thermometry based on the EIR of Dy3+ was proposed to be independent of the excitation wavelength and only excitation peak intensities required, with the merit of high absolute and relative sensitivities, excellent repeatability and reusability, good excitation wavelength selectivity. These findings demonstrated an effective strategy for developing a Dy3+-based EIR luminescent thermometer, as well as the enormous potential of Dy3+ doped CaWO4 phosphors in temperature sensing.

Effect of dopant concentration on the optical characteristics of Cr3+:ZnGa2O4 transparent ceramics exhibiting persistent luminescence

ZnGa2O4 (ZGO) persistent luminescence (PersL) ceramics doped with different concentrations of Cr3+ were prepared by the co-precipitation method and hot isostatic pressing (HIP) post-treatment. After HIP post-treatment, the ZGO PersL ceramics was significantly improved from opaque to transparent visual appearance due to the elimination of micro-pores during HIP process. The effects of Cr3+ concentration on the morphology, transmittance and PersL properties of ZGO PersL ceramics were systematically investigated. The ZGO PersL ceramics with higher Cr3+ dopant concentrations show less micro-pores and higher transmittance, which indicates that the Cr3+ can also work as a sintering additive to increase the density and to improve the optical quality of ZGO PersL ceramics. The photoluminescence excitation (PLE) and emission (PL) intensities increase with the increase of Cr3+ concentration up to 0.25 at.%. At yet higher Cr3+ concentrations, the ZGO PersL ceramics exhibits weaker PL and PLE intensities which is probably caused by the concentration quenching effect. However, the PersL decay curves show that the PersL performance of ZGO ceramics increases with increasing Cr3+ concentrations, indicating that the doping by Cr3+ ions may cause another traps formation leading to stronger and longer PersL. The PersL decay curves of all ZGO PersL ceramics were fitted by the second-order exponential function, indicating that at least two kinds of traps with different electron release rates exist in the ZGO ceramics. The influence of Cr3+ concentration on the thermoluminescence (TL) of ZGO PersL ceramics was also studied, and the results showed that the TL curves of the pre-sintered ceramics shifted to lower temperatures, indicating that the depth of trap related to Cr3+ ions is shallower than the depth of trap caused by the intrinsic defects.

Green synthesis, structure feature and energy transfer of yellow‐emitting (Y,Gd)2O2SO4:Dy phosphors

AbstractA green chemical precipitation route was used to yield a hydrated basic sulfate precursor upon calcination at 1000°C into a series of (Y,Gd)2O2SO4:Dy particles. The phosphors exhibited characteristic Dy3+ emissions from 4F9/2→6HJ (J = 15/2, 13/2, 11/2) transitions under ultraviolet light excitation; the quenching concentration of Dy3+ was determined to be 2.5 at.%. Substitution of Gd3+ for Y3+ led to an additional strong sharp band at ~277 nm (8S7/2→6IJ transition of Gd3+) in the photoluminescence excitation spectra, upon which the (Gd0.975Dy0.025)2O2SO4 phosphor achieved a ~2.8‐fold higher photoluminescence intensity via an effective energy transfer from Gd3+ to Dy3+ compared with the 354 nm excitation of Dy3+. Both the photoluminescence and photoluminescence excitation intensities of (Y,Gd)2O2SO4:Dy phosphors increased with rising Gd3+ concentration and calcination temperature in the range 750–1000°C. A higher Gd3+ concentration slightly prolonged the effective fluorescence lifetime.

Production and optical properties of Ce3+‐activated and Lu3+‐stabilized transparent gadolinium aluminate garnet ceramics

AbstractWe first report the novel Ce3+‐activated and Lu3+‐stabilized gadolinium aluminate garnet (GAG) transparent ceramics derived from their precipitation precursors via a facile co‐precipitation strategy using ammonium hydrogen carbonate (AHC) as the precipitant. The resulting precursors in liquid phase were substantially homogeneous solid solutions and could directly convert into sinterable garnet powders via pyrolysis. Substituting 35 at.% of Lu3+ for Gd3+ was effective to stabilize the cubic GAG garnet structure and transparent (Gd,Lu)3Al5O12:Ce ceramics were successfully fabricated by vacuum sintering at 1715°C. The ceramic transparency was improved by optimizing the particle processing conditions and the best sample had an in‐line transmittance of ~70% at 580 nm (Ce3+ emission center) and over 80% in partial infrared region with a fine average grain size of ~4.5 μm. Transparent (Gd,Lu)3Al5O12:Ce ceramics have a short critical wavelength (<200 nm) and a maximal infrared cut‐off at ~6.6 μm. Both the (Gd,Lu)3Al5O12:Ce phosphor powder and the transparent ceramic exhibited characteristic yellow emission of Ce3+ with strong broad emission bands from 490 to 750 nm upon UV excitation into two groups of broad bands around 340 and 470 nm. The photoluminescence and photoluminescence excitation intensities as well as the quantum yield were greatly enhanced via high‐temperature densification. Both the phosphor powder and ceramic bulk had short effective fluorescence lifetimes.

Valence Band Mixing in GaAs/AlGaAs Quantum Wells Adjacent to Self-Assembled InAlAs Antidots

Optical properties of GaAs/AlGaAs quantum wells (QWs) in the vicinity of InAlAs quantum dots (QDs) were studied and compared with a theoretical model to clarify how the QD strain affects the electronic states in the nearby QW. In0.4Al0.6As QDs are embedded at the top of the QWs; the QD layer acts as a source of strain as well as an energy barrier. Photoluminescence excitation (PLE) measurements showed that the QD formation leads to the increase in the ratio Ie-lh/Ie-hh of the PLE intensities for the light hole (lh) and the heavy hole (hh), indicating the presence of the valence band mixing. We also theoretically calculated the hh-lh mixing in the QW due to the nearby QD strain and evaluated the PLE ratio Ie-lh/Ie-hh.

One-Pot Facile Synthesis of Graphene Quantum Dots from Rice Husks for Fe3+ Sensing

In this work, graphene quantum dots (GQDs) with an average size of 3.9 nm were synthesized using rice husk biomass as the raw material via a facile one-step one-pot hydrothermal method. The size and morphology of the rice husk-derived GQDs were characterized by transmission electron microscopy and atomic force microscopy. The GQDs exhibit bright blue photoluminescence under 365 nm ultraviolet irradiation and can be well dispersed in water. The GQDs reach the strongest photoluminescence excitation intensity at ca. 360 nm under an emission wavelength of 466 nm, suggesting that the GQDs were oxidized with oxygenous groups attached. The quenching tests showed that the synthesized GQDs were highly and selectively sensitive toward Fe3+ ions and thus can potentially be used for Fe3+ sensing.

Effect of annealing in hydrogen atmosphere on the photoluminescence properties of phosphor-in- glass in tellurate glass

A series of phosphor-in-glasses (PIGs) was prepared by one-step melt-quenching method sintering the mixture of tellurate raw material powder and YAG:Ce3+ phosphors at 450–700°C, of which some was annealed at 250°C for 3h under the hydrogen atmosphere. The test results show that the relative photoluminescence (PL) intensity of phosphor-in-glass sintered at 450–700°C was significantly strengthened from 42.29% to 174.72% after the hydrogen annealing, and the relative photoluminescence excitation (PLE) intensity from 21.00% to 207.90%. However, the relative photoluminescence intensity of the PIG sintered at 700°C before and after hydrogen annealing was nearly zero because of the destruction of crystal structural surrounding Ce3+ ion. The concentration of Ce3+ and Ce4+ measured by X-ray photoelectron spectrum analyser (XPS) in PIGs before and after hydrogen annealing obviously happened to change, which was associated with the variation of PL and PL excitation intensity. Besides, the X-ray diffraction (XRD) pattern of YAG:Ce3+ phosphor and PIGs sintered at different temperatures further presented the destruction of YAG:Ce3+ lattice as the sintering temperature increased. Therefore, the appropriate sintering temperature and hydrogen annealing can increase the PL and PLE intensity and the Ce3+ concentration.

Drastic enhancement of blue-to-orange color conversion efficiency in heavily-doped ZnS:Mn2+ phosphor and its application in white LEDs

Heavily-doped ZnS:Mn2+ phosphors showed an extremely enhanced photoluminescence excitation intensity at 464nm peak wavelength originated from 6A1(6S)→4A1(4G) forbidden transition of Mn2+ ions. The best ZnS: Mn2+ phosphors showed the intensive orange color emission of 584nm peak wavelength from 4T1(4G) → 6A1(6S) forbidden transitions with an excellent lumen maintenance of 97% at 200°C, and their quantum efficiency of 75% under the 464nm excitation wavelength. The photoluminescence enhancement was explained in terms of the relaxation of selection rule on the forbidden intra-transitions of Mn2+ ion. It was caused by the spin-spin and the electron-phonon interactions supported by electron spin resonance signal and Raman spectroscopy, respectively. The excellent lumen maintenance was explained in terms of resonance-assistant direct intra-transition caused by the coupling between an excited electron (e*) on the 4A1(4G) state and multi-phonon energy. To evaluate its feasibility for white light-emitting diodes, the optimized ZnS:Mn2+ phosphor and its mixture with a green Lu3Al5O12:Ce3+ phosphor were applied to a 460nm blue-light-emitting diode. It showed high luminous efficiency of 68lm/W, suggesting a possibility on the application of Mn-doped ZnS phosphor for pc-WLED.

Efficient energy transfer from 1,3,5-tris(N-phenylbenzimidazol-2,yl) benzene to Mn:CdS quantum dots

In this work, we reported the energy transfer between Mn doped CdS quantum dots (Mn:CdS QDs) with the core–shell structure of MnS/ZnS/CdS and 1,3,5-tris(N-phenylbenz-imidazol-2,yl) benzene (TPBI) in inorganic/organic blend films by steady-state and time-resolved photoluminescence (PL) spectroscopy. The changes in PL excitation intensity of the Mn:CdS QDs and PL lifetime of the TPBI clearly demonstrate an efficient energy transfer process from TPBI to QDs in the blend films. Further, it is found that the efficiency of Förster resonance energy transfer increases with the increasing of the thicknesses of CdS shell. These results highlight the potential of Mn doped QDs for fabricating high-performance QD light-emitting diodes.

Optical excitation and emission processes of Si-QD/SiO2 multilayer films with different SiO2 layer thicknesses

Si-rich oxide/SiO2 multilayer films with different SiO2 layer thicknesses have been deposited by the plasma enhanced chemical vapor deposition technique, and crystallized Si quantum dot (Si-QD)/SiO2 multilayer films are obtained after annealing at 1100 ∘C. The photoluminescence (PL) intensity of the multilayer films increases significantly with increasing SiO2 layer thickness, and the PL peak shifts from 1.25 eV to 1.34 eV. The PL excitation spectra indicate that the maximal PL excitation intensity is located at 4.1 eV, and an excitation–transfer mechanism exists in the excitation processes. The PL decay time for a certain wavelength is a constant when the SiO2 thickness is larger than 2 nm, and a slow PL decay process is obtained when the SiO2 layer is 1 nm. In addition, the PL peak shifts toward high energy with decreasing temperature only when the SiO2 layer is thick enough. Detailed analyses show that the mechanism of PL changes from the quantum confinement effect to interface defects with decreasing SiO2 layer thickness.

Effect of Particle Size on the Optical Properties of Yellow Silicate Phosphor in Light‐Emitting Diodes

Understanding the effect of particle size on the optical properties of phosphor is important to increase packaging efficiency in white light‐emitting diodes (LEDs). We have investigated the effect of particle size (10–20 μm, 20–25 μm, 25–32 μm) on the optical properties of a yellow silicate phosphor adopted in white LEDs. X‐ray diffraction results show negligible modification in crystallinity as the particle size of the yellow silicate phosphor varies, whereas the photoluminescence excitation intensity and quantum yield are enhanced as the particle size increased. LED packages fabricated using phosphors with different mean particle sizes, and their optical properties were analyzed. The radiant flux improved with increasing particle size, whereas the luminous flux increased with decreasing particle size. The effect of immersion on the optical properties of the LED light source has been also measured, and the details are discussed.

Analysing the photoluminescence intensities of single‐walled carbon nanotubes

AbstractWe study the photoluminescence and photoluminescence excitation intensities of single‐walled carbon nanotubes. To derive the chirality fractions of semiconducting tubes from these optical methods requires a thorough analysis of the experimental parameters and the lifetimes of the excitonic states. We obtain the intensity distribution from the product of the widths of the first and second excitonic transition and the intensity of the absorption of the second excited state. Compared with previous analysis protocols our intensity distribution points towards a chirality abundance which is (i) narrower in diameter, (ii) centred at smaller diameters and (iii) more strongly dominated by armchair‐like tubes. We present a recipe for the fit of luminescence data.

Size- and Composition-Dependent Energy Transfer from Charge Transporting Materials to ZnCuInS Quantum Dots

We studied the energy transfer processes from organic charge transporting materials (CTMs) to ZnCuInS (ZCIS) quantum dots (QDs) with different emission wavelength by steady-state and time-resolved photoluminescence (PL) spectroscopy. The change in the PL excitation intensity of the ZCIS QDs and the PL decay time of the CTMs clearly demonstrated an efficient energy transfer process in the ZCIS/CTM blend films. It was found that the efficiency of Förster resonance energy transfer significantly increases with increasing the particle size and decreasing the Zn content in the QDs, which is well consistent with the estimated Förster radii (R0) varying from 3 to 5 nm. In addition, the PL quenching of the QDs related to the charge separation process was also observed in some of the samples. The energy transfer and charge separation processes in the films were well explained based on the band alignment between the ZCIS QDs and CTMs.

Optical and electrical properties of Si-doped GaAs films grown on (631)-oriented substrates

This work studies the Si-doping of GaAs on (631)-oriented substrates as a function of the As4-beam equivalent pressure (PAs). The electrical properties obtained by Hall effect measurements show that the mobility of the layers grown on (631)-substrates present changes related to carrier compensation processes and the Si-doping changes from p- to n-type when PAs is increased. The optical properties of the samples, as observed by photoluminescence (PL) spectroscopy, modified according to the electrical characteristics. For (631)-samples, when PAs is increased the energy of the maximum intensity PL peak redshifts in the p-type region but, after the threshold of the conduction type conversion, the peak blueshifts in the n-type region. The variation of the PL excitation intensity also shifts the emission energy of the samples as a consequence of the increasing recombination rate for close pairs in donor acceptor pair recombination. Photoluminescence as a function of temperature shows that the activation energy of the PL lines transition is enhanced as PAs is increased.

Photoluminescence Enhancement of Synthesized ZnS-Based-Nanocrystals and Aging Effect on Its Emitting Color

Various colors-emitting ZnS:Cu,Cl, ZnS:Cu,Cl,Mn and ZnS:Mn nanocrystals (NCs) which were shown to be about 3 nm sized-particle were synthesized by using a solution chemistry. And the luminescences of the synthesized ZnS-based NCs were investigated through photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopy. The PLE and PL intensities of the ZnS-based NCs depends on their reflux time, and red shifted maximum PLE wavelengths of the synthesized NCs showed with increasing reflux time. The increased maximum PL intensity of NCs with increasing reflux time is due to the enhanced crystallinity of the NCs. And the shifted emitting colors of the NCs showed after aging treatment compared to those of refluxed NCs. The amount of shifted wavelength of Cu,CI doped ZnS, Cu,CI and Mn co-doped ZnS, only Mn doped ZnS NCs were -22 nm, +18 nm, and +14 nm, respectively.

Surface-plasmon-assisted modal gain enhancement in Au-hybrid CdSe/ZnS nanocrystal quantum dots

Surface-plasmon-assisted modal gain enhancement was investigated in Au-hybrid CdSe/ZnS nanocrystal quantum dots. A fivefold enhancement of the modal gain was observed at room temperature in the presence of a Au film by using modal gain contour map analysis, and the photoluminescence intensity and size-selective photoluminescence excitation intensity increased significantly. The enhanced modal gain was attributed to the multiexciton states of neutral and charged biexciton and triexciton.

Near-band-edge photoluminescnce in Cu(In,Ga)Se 2 solar cells

Photoluminescence (PL) and PL decay characteristics of the near-band-edge (NBE) PL at room temperature have been studied on the Cu(In,Ga)Se 2 (CIGS) solar cells. The carrier recombination process has been discussed with emphasis on the photovoltaic properties of the solar cell. It has been found that: (i) PL intensity of the CIGS solar cells is much stronger than that in the corresponding CIGS thin films, (ii) the PL decay time of the cell is longer than that of the CIGS film, and (iii) the PL decay time of the CIGS solar cell exhibits strong dependence on the PL excitation intensity. In the CIGS solar cell, intense PL is obtained under the open circuit condition (oc), in contrast to the very low PL yield under the short circuit (sc) condition. The PL decay time under the sc condition is much shorter than that under the oc condition. Excitation intensity dependence of PL intensity and the PL decay time have been studied, and they are discussed with relation to the photo-voltage due to the PL excitation light. PL and injection EL under the external DC bias have been studied. The mapping image of NBE-PL intensity has been compared with that of the laser beam induced current (LBIC), and the PL intensity image reflects the photovoltaic properties of the CIGS solar cells. We demonstrated that NBE-PL of the CIGS solar cell reflects the photovoltaic effect, and it can be utilized as a powerful characterization method.

Enrichment of (8,4) Single‐Walled Carbon Nanotubes Through Coextraction with Heparin

Heparin sodium salt is investigated as a dispersant for dispersing single-walled carbon nanotubes (SWNTs). Photoluminescence excitation (PLE) spectroscopy is used for identification and abundance estimation of the chiral species. It is found that heparin sodium salt preferentially disperses larger-diameter Hipco SWNTs. When used to disperse CoMoCAT nanotube samples, heparin has a strong preference for (8,4) tubes, which have larger diameter than the predominant (6,5) in pristine CoMoCAT samples. PLE intensity due to (8,4) tubes increases from 7% to 60% of the total after threefold extractions. Computer modeling verifies that the complex of (8,4) SWNTs and heparin has the lowest binding energy amongst the four semiconducting species present in CoMoCAT. Network field-effect transistors are successfully made with CoMoCAT/heparin and CoMoCAT/sodium dodecylbenzene sulfonate (SDBS)-heparin (x3), confirming the easy removability of heparin.