Photoluminescence Degradation Research Articles

Photoluminescence degradation mechanism of BaMgAl10O17:Eu2+ phosphor by vacuum ultraviolet irradiation

A real high power vacuum ultraviolet light source is applied to the investigation on the vacuum ultraviolet irradiation degradation of BaMgAl10O17:Eu2+ phosphor. The degradations of emission intensity and color quality of the sample are clearly observed after irradiation. It reveals that the oxidation of Eu2+ during irradiation is partly responsible for the degradations. The excitation and absorption spectra show that some traps generated during irradiation have negative influence on the luminescence of sample and these traps have been identified as positively charged oxygen vacancies by positron annihilation. The investigations on host emission and decay curve further confirm that these oxygen vacancies are involved in the perturbation of energy transfer from the host to Eu2+ and finally result in the degradation.

Characterization of Oxygen Vacancy Associates within Hydrogenated TiO2: A Positron Annihilation Study

This paper introduces a novel method for characterizing the oxygen vacancy associates in hydrogenation-modified TiO2 by using a positron annihilation lifetime spectroscopy (PALS). It was found that a huge number of small neutral Ti3+–oxygen vacancy associates, some larger size vacancy clusters, and a few voids of vacancy associates were introduced into hydrogenated TiO2. The defects blurred the atomic lattice high-resolution transmission electron microscopy (HRTEM) images and brought about the emergence of new Raman vibration. X-ray photoelectron spectroscopy (XPS) measurement indicated that the concentration of oxygen vacancies was 3% in the TiO2 lattice. The photoluminescence (PL) spectroscopy, photocurrent, and degradation of methylene blue indicated that the oxygen vacancy associates introduced by hydrogenation retarded the charge recombination and therefore improved the photocatalytic activity remarkably.

The Thermal Stability and Photoluminescence Degradation of Mn2+in Fluorescent Lamp used BaMgAl10O17:Eu2+,Mn2+Phosphor

The thermal stability and photoluminescence degradation of Mn2+ in fluorescent lamps used BaMgAl10O17:Eu2+,Mn2+ phosphor are investigated. The detection of impurity containing manganese with high valence demonstrates the oxidation of Mn2+ during baking process at 700°C and it partly leads to emission degradation of Mn2+. The emission of Mn2+ mainly originates from the energy transfer of Eu2+→Mn2+. The oxidation of Eu2+ decrease the amount of Eu2+ centers and thus finally causes the degradation of Mn2+. Some traps are revealed to be induced during baking process and it further weakens energy transfer efficiency of Eu2+→Mn2+ and decreases the emission of Mn2+.

Effects of Plasma Processes on the Characteristics of Optical Device Structures Based on GaAs

We investigate the effects of inductively coupled O2 plasma ashing, capacitively coupled C3F8 plasma etching, and capacitively coupled C3F8/O2 plasma etching on the optical and electrical characteristics of GaAs-related optical device structures. The O2 plasma ashing produces non radiative recombination centers close to the sample surface. The sample with a cap AlGaAs layer prevents the degradation of photoluminescence (PL) intensity, probably inhibiting the penetration of damaging ions into the buried quantum well. The C3F8 plasma etching also degrades the PL intensity; however, under moderate conditions, the effect of non radiative surface recombination can be suppressed by the formation of a surface oxide layer. On the other hand, the formation of oxide increases the specific contact resistance (ρc) of the electrode. The etching with C3F8/O2 mixed plasma also deteriorates the optical characteristics presumably owing to the synthesized impact of the constituent gases, while it has limited effect on ρc.

Improved moisture resistance of SrSO4:Sm3+ phosphors coated with SiO2

SrSO4:Sm3+ phosphors obtained by precipitation method are coated with SiO2 and their photoluminescence (PL) degradation behavior is investigated. The SiO2 coating is obtained by the ultrasonic sonochemical process using tetraethylorthosilicate (TEOS) as silicon coating reagent and the coating content is varied from 0.5 to 2wt%. Powder X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), fluorescence spectrometer, and Fourier transform infrared spectrometer are employed to characterize the coating. Moisture resistances of coated SrSO4:Sm3+ phosphors have been enhanced to a great degree without more loss of their optical properties based on the existence of the SiO2 thin layer. The PL intensity of the coated phosphors decreases to ∼83% of the original value after 38h soaking the phosphors in deionized water, while the uncoated phosphor decreases to ∼40%.

Reversible Degradation of Photoluminescence in Si/SiGe Three Dimensional Nanostructures

ABSTRACTWe report the degradation of low temperature photoluminescence (PL) from Si/SiGe three-dimensional cluster morphology nanostructures under continuous photoexcitation. The PL intensity initially decreases slowly for about 15 minutes, and then decreases rapidly, until only ∼ 10% of the original PL intensity remains. A complete recovery of the PL requires restoring the sample temperature to ∼ 300K. We propose that a slow accumulation of charge in SiGe clusters enhances the rate of Auger recombination and results in the observed PL degradation.

Photoluminescence and photocatalytic degradation studies on some metallophthalocyanines

This paper deals with the up-conversion intrinsic photoluminescence by exciting the Metallo-Phthalocyanine (MPc) prepared by melt method. MPcs were further characterized using UV visible spectrophotometer, FT-IR, and thermal analysis. The magnetic susceptibility, optical absorption and photoluminescence behavior of these compounds were studied. Photocatalytic degradation of amido black 10B dye using different MPcs at varing pH was done to see the efficiency of these compounds. High emission intensity and easy preparation makes these systems potential candidates for application as luminescent material.

PL and CL degradation and characteristics of SrAl2O4: Eu2+,Dy3+ phosphors

Strontium aluminate phosphors are ideal for luminescent infrastructure materials. Their brightness and persistent glow time are much higher than previously used sulphide phosphors. Strontium aluminates prepared by the sol–gel and combustion methods are compared with commercially available strontium aluminate. High luminescent efficient SrAl2O4:Eu2+,Dy3+ pulsed laser deposited (PLD) thin films were also produced using the commercially available powder. Photoluminescence (PL) degradation studies showed that the phosphor intensity decreased about 20% over a period of 2 weeks under ultraviolet (UV) irradiation. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) showed that cathodoluminescence (CL) degradation is due to the formation of SrO due to electron stimulated surface reactions. The light output mechanism of the phosphor is also discussed in more detail.

Quenching influence of cell culture medium on photoluminescence and morphological structure of porous silicon

In this work, the degradation of visible photoluminescence of porous silicon (PSi) under the influential actions of cell culture medium has been mainly studied in order to comprehend the quenching mechanisms necessitating the cell growth on spongy-like-silicon structures, which could form either micro- and/or nano-dimensional morphologies after stain-etching of the poly- or single-crystalline Si surfaces. Quenching effect of the neuron culture medium on visibly luminescent and non-luminescent porous silicon is found to be quite obvious so that this step of the culture process, especially, over nanostructured silicon is extremely essential for a variety of bionanotechnological applications.

Anomalous long-term degradation of photoluminescence in porous silicon layers

The main systematic features of degradation of photoluminescence of porous silicon layers during long-term storage in air are studied. A profound increase in the photoluminescence intensity and a shift of the photoluminescence peak to shorter wavelengths in the optical spectra are observed for all samples. It is found that the degree of degradation depends on the initial crystallographic orientation of the silicon substrate. The decrease in the average diameters of silicon nanoclusters in porous silicon samples is attributed to chemical processes that occur at the developed porous surface with participation of atmospheric oxygen.

Improving stability of photoluminescence of ZnSe thin films grown by molecular beam epitaxy by incorporating Cl dopant

This investigation studies the effect of chlorine (Cl) dopant in ZnSe thin films that were grown by molecular beam epitaxy on their photoluminescence (PL) and the stability thereof. Free excitonic emission was observed at room-temperature in the Cl-doped sample. Photon irradiation with a wavelength of 404 nm and a power density of 9.1 W/cm2 has a much stronger effect on PL degradation than does thermal heating to a temperature of 150 °C. Additionally, this study shows that the generation of nonradiative centers by both photon irradiation and thermal heating can be greatly inhibited by incorporating Cl dopant.

The role of surface oxidation on luminescence degradation of porous silicon

This study reports a comparative analysis on time dependent degradation of photoluminescence (PL) spectra of porous silicon (PS) during dark-aging (DA) and photo-aging (PA). Fourier Transform Infrared (FTIR) spectroscopy studies have been performed to get an insight on possible chemical changes in the PS surface. It has been found that SiHx bonds decrease progressively while SiOx bonds increase. FTIR and PL measurements revealed presence of blue shifts in the PL spectra during the aging stages (PA and DA). While the PL intensity of dark aged PS shows a decrease during the first 3 weeks and an increase afterwards, the PL intensity decreases continuously for photo-aged PS. The change in the PL spectra has been investigated by overlapping of two different PL bands which are reflective of oxidation of PS surface and size of Si naonocrystallites. A possible bond configuration model about the oxidation of PS surface has also been proposed. The results are interpreted in terms of quantum size effects in PS and the influence of the surface composition.

Improved moisture resistance of SrS:Eu 2+ phosphors with nanoscale SiO 2 coating

Orange-emitting SrS:Eu 2+ phosphors were coated with nanoscale SiO 2 and their photoluminescence (PL) degradation behavior in moist air was investigated. The SiO 2 coating was obtained by sol–gel process using diethoxydimethylsilane (DEDMS) and the coating content was varied from 0.5 to 2 wt%. The coatings were composed of a uniform, continuous, and amorphous SiO 2 layer of 30–50 nm thickness and the coating thickness was not varied significantly with the coating content. No peak shift and no decrease of PL intensity were observed after coating. The PL intensity of the coated phosphors decreased to ∼75% of the original value after 10 h exposure to moist air, while the uncoated phosphor decreased to ∼33%, which indicates the improved moisture resistance of the nanoscale SiO 2 coated SrS:Eu 2+ phosphors.

Highly luminescent quantum dots functionalized and their conjugation with IgG

A sol–gel approach including partially removing capping agents, depositing SiO 2 monomers, and growing a SiO 2 shell was developed to generate a bio-compatible functionalization on CdTe quantum dots (QDs). The QDs retained their high photoluminescence (PL) efficiency after coating with a SiO 2 shell (22.5%) by controlling the surface state of the QDs to decrease PL degradation during a sol–gel preparation. Furthermore, the CdTe QDs with a SiO 2 shell were conjugated with IgG using 3-sulfo-N-hydroxysuccinimide or streptavidin–maleimide as linkers. The biotin–streptavidin linker resulted in a high PL efficiency retained (only ∼23% lower than the initial value of the QDs), which is crucial for bio-applications.

Use of ultra-thin aluminum oxide layer to reduce photoluminescence decay in poly(p-phenylene vinylene) films

The degradation of conjugated polymer poly(p-phenylene vinylene) (PPV) in the atmosphere upon exposure to ultraviolet light limits its applications as the emitting layer in organic light emitting diodes. In this paper we show that a thin layer of aluminum oxide around 10 nm in thickness prevents photoluminescence degradation of PPV during exposure to blue light in the atmosphere but not at lower excitation wavelengths. This oxide film is free of cracks and pinholes from transmission electron microscopy analysis.

Heat-treatment-induced luminescence degradation in Tb 3+-doped CePO 4 nanorods

CePO 4:Tb nanorods were synthesized via a simple wet-chemical route. The as-synthesized CePO 4:Tb nanorods present high photoluminescence efficiency due to an efficient energy transfer form Ce 3+ to Tb 3+. However, heat treatment at 150 °C in air leads to a significant decrease of photoluminescence. X-ray photoelectron spectroscopy and excitation spectra revealed the oxidation of Ce 3+ to Ce 4+ in the heat-treatment process, which should be responsible for significant photoluminescence degradation due to the breakage of Ce 3+→Tb 3+ energy transfer. This conclusion is further supported by atmosphere and size effects of photoluminescence of CePO 4:Tb under the heat treatment.

Structural and optical properties of GaAs(001) surfaces thermally annealed in dry N2 atmosphere

Thermal annealing behaviors of GaAs(001) surfaces in dry N2 atmosphere have been studied by using spectroscopic ellipsometry (SE), optical microscopy, scanning electron microscopy, ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) techniques. The SE data indicate that thermal annealing at temperatures T below 500 °C causes no or a little influence on the surface morphology. Microscopic roughening starts to occur at T>600 °C and exhibits a saturated roughness value at ∼800 °C. AFM observation confirms the presence of a microscopically roughened surface overlayer after annealing at T∼600–750 °C and a macroscopically roughened overlayer at above 700 °C. The XPS data indicate the removal of As2O3 oxide after annealing at above 500 °C; however, the Ga2O3 oxide is always observed regardless of annealing temperature, although its peak intensity becomes remarkably large at T∼700 °C and small at T≥800 °C. Annealing at T=1000 °C leads to deliquesced sample surface. The native GaAs oxide is also found to act as a passivation film against annealing-induced PL degradation for T below ∼400 °C.

Properties of GaAs(001) surfaces thermally annealed in vacuum

Thermal degradation of GaAs(001) surfaces has been studied using spectroscopic ellipsometry (SE), optical microscopy, ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) techniques. The SE data suggest that thermal annealing causes no or little influence on the surface native oxide layer at temperatures T≤500 °C. Microscopic roughening starts to occur on GaAs surface at T>500 °C, giving maximum AFM roughness (rms∼14 nm) at 540 °C, and then tends to smoothened at T>540 °C (rms∼2.5 nm at 580 °C). Macroscopically roughened surfaces are observed at T>500 °C, becoming more pronounced at higher annealing temperature. The Ga droplets are also observed at T≥600 °C that lead to catastrophically damaged surfaces and make SE measurement impossible. The XPS data indicate thinning of the native GaAs oxide in the limited temperature range 450<T<580 °C; however, annealing at T≥580 °C leads to coverage with thermal oxides (Ga2O and As2O3). The naturally grown GaAs oxide is also found to act as a good passivation film against annealing-induced PL degradation.

PL Degradation을 활용한 OLED 소자의 사진 이미지 구현

We have realized static image on organic light emitting diodes (OLEDs) using photoluminescence degradation. Ultraviolet (UV) was irradiated to the glass side of device. UV power was 350 Wand the wavelength was 365 nm. The UV irradiation gives rise to the degradation of photoluminescence. Due to the degradation, the current density-voltage curve was shifted to the higher voltage side and the luminescence was also degraded by the current and photoluminescence drop. The negative imaged films were prepared to control the transmittance of UV. The UV light was passed through the film. By this method, the film image was transferred to the device with reversed image and the static image was realized on the OLED.

Structure, paramagnetic defects and light-emission of carbon-rich a-SiC:H films

The effect of vacuum annealing on local structure reconstruction, evolution of photoluminescence (PL) and paramagnetic defects in carbon-rich a-Si1−xCx:H films (x=0.7) was studied. Strong enhancement of visible (white-green) PL was observed after annealing in the temperature range of 400–500 °C. Such enhancement was correlated with increasing of the concentration of carbon-hydrogen bonds in Si:CHn accompanied with increase in the fluctuation of the interatomic potential. Complete disappearance of PL, “graphitization” of the carbon precipitates, and a strong increase in the concentration of the paramagnetic states were observed after annealing at 650 °C and above. The enhancement and the degradation of PL after different-temperature treatments are explained by the following competing effects: (1) enhancement of the radiative recombination due to passivation of paramagnetic defects with hydrogen and increase of localization of photoexcited electron-hole pairs due to formation of new Si:CH and (2) enhancement of the nonradiative recombination through the paramagnetic states due to increase in their concentration caused by graphitization of carbon precipitates after high- temperature treatment.