Cathodoluminescence Measurements Research Articles

Growth of Zr/ZrO2 Core–Shell Structures by Fast Thermal Oxidation

This research has been conducted to characterize and validate resistive heating as a synthesis method for zirconium oxides (ZrO2). A wire of Zr has been oxidized to form a core–shell structure, in which the core is a metal wire, and the shell is an oxide layer that is around 10 μm thick. The characterization of the samples has been performed by means of several techniques based on Scanning Electron Microscopy (SEM). The topography images show that thermal gradient appears to have little influence on morphology, unlike time, which plays an important role. The chemical composition was analyzed by X-ray spectroscopy (EDX) and X-ray diffraction (XRD), and Raman spectroscopy has been used to assess crystallinity and crystal structure. The oxide layer is mainly formed by monoclinic ZrO2, alongside other, less significant, phases. Photoluminescence (PL) and cathodoluminescence (CL) measurements have allowed us to study the distribution of defects along the shell and to confirm the degree of uniformity. The oxygen vacancies, either as isolated defects or forming complexes with impurities, play a determinant role in the luminescent processes. Color centers, mainly electron centers such as F, FA and FAA, give rise to several visible emissions extending from blue to green, with main components at around 2 eV, 2.4–2.5 eV and 2.7 eV. The differences between PL and CL in relation to distinct recombination paths are also discussed.

Impact of neutron irradiation on electronic carrier transport properties in Ga2O3 and comparison with proton irradiation effects

The minority charge carrier transport in beta gallium oxide (-Ga2O3) before and after exposure to neutrons from a 241Am-Be source was studied. Cathodoluminescence (CL) spectroscopy and current–voltage (I-V) characteristics were used to study minority carrier behavior. High energy radiation affects minority carrier properties through the production of carrier traps that reduce the conductivity and mobility of the material. In this paper, we report the effects of neutron radiation in silicon-doped -Ga2O3, using rectifiers or transistors as the measurement platform. The thermal activation energy of the reference (non-irradiated) sample was 40.9 meV, which is ascribed to silicon-donors. CL measurements indicate a slightly indirect bandgap energy of 4.9 eV. Neutrons create disordered regions in -Ga2O3 rather than just point defects, resulting in the lowest carrier removal rate because of the lowest average non-ionizing energy loss. The neutron irradiation caused an increase in reverse bias leakage current in rectifiers and a carrier removal rate of 480 cm−1 but had little effect on reverse recovery switching time. Differences in CL spectra were observed between vertical and lateral device structures, emphasizing the importance of impurities and defects in the starting material. The neutron energies in the Am-Be source range up to 11 MeV, with an average energy between 4 and 5 MeV (Figure 1). We also contrasted neutron damage with the effects of irradiation with 10 MeV protons. Under 10 MeV proton irradiation, the thermal activation energies increase. This is attributable to high order defects and their influence on carrier lifetimes. The measurements show that -Ga2O3 is more resistant to radiation damage than other wide bandgap semiconductors due to its higher displacement threshold energy, which is inversely proportional to the lattice constant.

Characterization of pulsed laser deposited La2O2S:Eu3+ thin films and effect of coating with graphene oxide layers

Surface coatings have been widely used to improve phosphor characteristics for the purpose of increasing luminescence intensity and protecting against degradation. In this study, an uncoated La2O2S:Eu3+ thin film is compared to films coated by graphene oxide, as prepared or annealed in an inert or reducing atmosphere. The characteristic red emission of Eu3+ ions was observed for all samples and attributed to 5D0-7F2 transitions, while no luminescence associated with graphene oxide was observed. The luminescence intensity from the as-coated sample and the one annealed in an inert Ar atmosphere was less, compared to the uncoated film, whereas the coated sample annealed in a reducing atmosphere (Ar/H2) had emission, which was of similar intensity to the uncoated sample. Its degradation, and that of the uncoated sample, were studied by recording Auger electron spectroscopy and cathodoluminescence measurements, simultaneously. During electron irradiation, the surface of the uncoated sample was converted to a much more luminescent layer as C and S were gradually removed from the surface. Auger electron spectroscopy measurements of the coated sample showed that even initially, it had almost no S on the surface. The loss of S was attributed to annealing in Ar/H2, where H2S gas may be produced as the phosphor was converted into La2O3. This La2O3 subsequently formed La(OH)3 due to its hydroscopic nature. Unlike the uncoated sample, from which C due to unintentional contamination was fairly easily removed from the surface, C on the surface of the coated sample became less but was resistant to removal, which was associated with the formation of CHLaO3 at the surface as suggested by x-ray diffraction. Although coating with graphene oxide did not result in chemically stable La2O2S:Eu3+ thin films, the cathodoluminescence intensity of both the uncoated and graphene oxide coated samples annealed in reducing atmosphere increased during electron beam exposure (with no change in the form of the emission spectra) so that such films may have potential cathodoluminescence applications.

Core-Shell Nanorods as Ultraviolet Light-Emitting Diodes.

Existing barriers to efficient deep ultraviolet (UV) light-emitting diodes (LEDs) may be reduced or overcome by moving away from conventional planar growth and toward three-dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency, and quantum wells free from the quantum-confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN core-shell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments, where we find low turn-on voltages, strongly rectifying behaviors and significant electron-beam-induced currents. Time-resolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarization fields. Our results show nanostructuring to be a promising route to deep-UV-emitting LEDs, achievable using commercially compatible methods.

Er:Y2O3 and Nd:Y2O3 Nanoparticles: Synthesis, Pegylation, Characterization and Study of Their Luminescence Properties

Lanthanide-doped yttrium oxide nanoparticles can display selective upconversion properties, rendering them invaluable in the field of nanomedicine for both sensing and diagnostics. Different syntheses of Er:Y2O3 and Nd:Y2O3 nanoparticles (NPs) were studied and optimized to obtain small particles of regular shape and good crystallinity. The morphological and compositional characterizations of the nanoparticles were obtained with different techniques and showed that both Er:Y2O3 and Nd:Y2O3 NPs were well dispersed, with dimensions of the order of a few tens of nanometers. The photoluminescence and cathodoluminescence measurements showed that both Er:Y2O3 and Nd:Y2O3 NPs had good emission as well as upconversion. The nanophosphors were functionalized by a pegylation procedure to suppress unwanted reactions of the NPs with other biological components, making the NP systems biocompatible and the NPs soluble in water and well dispersed. The pegylated core/shell nanoparticles showed the same morphological and optical characteristics as the core, promoting their strategic role as photoactive material for theragnostics and biosensing.

Enhancement of excitonic and defect-related luminescence in neutron transmutation doped β−Ga2O3

Neutron irradiation analysis, inductively coupled plasma mass spectrometry (ICPMS), and cathodoluminescence (CL) spectroscopy are used to investigate the influence of transmuted Ge incorporation on the luminescence properties of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ single crystals. Calculations based on ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$-neutron interaction reveal temporal variations of both Ge and Zn concentrations as a function of time during and after neutron irradiation. To produce a concentration of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.16em}{0ex}}\mathrm{Ge}\phantom{\rule{0.16em}{0ex}}\mathrm{donors}/\mathrm{c}{\mathrm{m}}^{3}$ from the neutron transmutation of Ga, the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystal was irradiated for 27 h, which was accompanied by the incorporation of ${10}^{16}\phantom{\rule{0.16em}{0ex}}\mathrm{Zn}\phantom{\rule{0.16em}{0ex}}\mathrm{acceptors}/\mathrm{c}{\mathrm{m}}^{3}$. These calculated dopant concentrations are confirmed by ICPMS. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystals exhibit a UV band at 3.40 eV due to self-trapped holes (STHs) and two blue donor-acceptor pair (DAP) peaks at 3.14 eV (BL1) and 2.92 eV (BL2). In addition to the neutron-induced incorporation of substitutional Ge donors and Zn acceptors on Ga sites, Ga vacancies (${V}_{\mathrm{Ga}}$) were created by high-energy neutrons in the flux, which strongly enhanced the BL1 peak. The ${V}_{\mathrm{Ga}}$ acceptors compensate the neutron-induced Ge donors, making the ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystal highly resistive. Concurrent temperature-resolved CL measurements of the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ before and after neutron irradiation reveal a twofold increase in both the STH and BL1 peaks. This result suggests that STHs are preferentially localized at an O site adjacent to ${V}_{\mathrm{Ga}}$, as theoretically predicted by Kananen et al. [Appl. Phys. Lett. 110, 202104 (2017).]. Analysis of the ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ CL temperature dependence reveals that the UV and BL1 bands after the neutron irradiation exhibit an equivalent activation energy of $100\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ due to the presence of a neutron-induced defect that acts as an efficient competitive nonradiative recombination channel. The results also provide evidence that the BL1 and BL2 bands arise from different DAP pairs.

III-V material growth on electrochemically porosified Ge substrates

III-V semiconductor materials for high-efficiency multi-junction solar cells are often grown on germanium (Ge) substrates. However, apart from being considered as a rare element, Ge substrates are one of the major cost shares of a III-V multi-junction solar cell. To reduce costs and material consumption, we aim at re-usable porosified Ge substrates. Prior to the growth, the porous layers are subjected to an annealing procedure to close the wafer surface and to form a predetermined breaking area some microns below the surface. Later, the III-V epitaxial layers are mechanically lifted at the porous layer, so the substrate can be reused. Here, we demonstrate the III-V epitaxy material quality by growing Al0.5Ga0.49In0.01As/Ga0.99In0.01As double heterostructures on porous Ge substrates and characterize them in detail to understand how the porous layers affect the structural and opto-electronic properties of theIII-Vcompounds compared to a reference grown on germanium “epi-ready” substrates. We find no significant influence of the porous Ge substrate on the layer’s composition, thickness or roughness. However, cathodoluminescence measurements reveal a defect density of 4.5 × 105 cm−2 in comparison with 6.8 × 104 cm−2 for the reference case. Those defects were identified as threading dislocations by electron channeling contrast imaging. The lifetime of minority carriers measured by time resolved photoluminescence shows no difference in the low injection regime between both samples either, indicating a high quality opto-electronic material deposited on porous Ge. These first promising results indicate a path for both: reducing costs of III-V multi-junction solar cells and a reduced germanium consumption.

Catastrophic optical damage in 808 nm broad area laser diodes: a study of the dark line defect propagation

We present a study of the propagation of dark line defects (DLDs) in catastrophically damaged 808 nm laser diodes, based on cathodoluminescence (CL) measurements and laser mode propagation simulations. Room temperature CL images show blurred DLDs running parallel to the laser cavity. Remarkably, low temperature images reveal their true morphology: the blurred lines are resolved as parallel narrow discontinuous DLDs. This morphology does not match the usually reported molten front scenario of DLD propagation. Low temperature images show that DLDs consist of a sequence of catastrophic optical damage (COD) events separated a few micrometers from each other. Consequently, a different propagation scheme is proposed. The points where the CODs occur suffer a temperature increase and these hot spots play a capital role in the propagation of the DLDs. Their influence on the beam distribution is modelled using finite element methods. The calculations evidence changes on the intensity distribution of the laser that qualitatively reproduce the DLD shapes. Additionally, the COD events result in the generation of defects in the region that surrounds them. The successive CODs in the discontinuous DLDs are rationalized in terms of the enhanced laser absorption in these sensitized regions where the laser beam is concentrated by thermal lensing.

Minority-carrier dynamics in β-gallium oxide probed by depth-resolved cathodoluminescence

The behavior of hole polarons in β-gallium oxide (Ga2O3) has attracted significant attention. Depth-resolved cathodoluminescence (CL) was used to investigate the minority carrier dynamics in β-Ga2O3. First, a model describing CL intensity was proposed by considering the depth-dose function and surface recombination. A universal depth-dose function for β-Ga2O3, which has the form of a third-degree polynomial, was presented based on Monte Carlo simulation by introducing a normalized depth, which is the depth normalized by the electron beam range. Second, two experimental approaches, plan-view and cross-sectional CL measurements, were applied to unintentionally doped β-Ga2O3 (−201) wafers, and the experimental results were compared with those of the proposed model. The hole diffusion length was estimated to be within the range of 200–400 nm through the plan-view measurement, whereas a hole diffusion length of 250 nm was obtained through the cross-sectional measurement. The values were consistent with each other, and the model reproduced the experimental results well. This indicates that the nonequilibrium minority hole in the unintentionally doped β-Ga2O3 is mobile and forms a ‘weak’ polaron. The reduced recombination velocity of the (−201) face was estimated to be approximately ten for the plan-view measurement, whereas that of ten or more was assumed for the cross-sectional measurement. No inconsistency was observed, but the low-energy plan-view measurement is considered more suitable for investigating the surface recombination velocity.

Physicochemical properties of Li3Ba2La3(MoO4)8:Eu,Tb red-emitting phosphor for solid state white lamps

In this work, combustion synthesis was used for the first time to fabricate a phosphor material with red emission for applications in solid-state white-light lamps. We synthesized a material with emission wavelength at λem = 617 nm, excited under long UV-blue wavelength based on Eu3+, Tb3+-activated molybdates Li3Ba2(La1–x–yEuxTby)3(MoO4)8 with 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. A series of powder samples were produced by the combustion method and post-annealed at 800 °C in air. The crystalline phase formation was investigated by X-ray diffraction, which reveals the monoclinic C2/c (15) space group. It is observed that crystalline structure and morphology are preserved when the host lattice is doped with Eu3+ or Tb3+ single ions and co-doped with both ions at different doping concentrations. A detailed characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) shows a similar morphology in all samples: rather large (1–7 μm) agglomerate particles with irregular shapes and surrounded by smaller nanoparticles of 50 nm in size. UV–visible absorption spectra confirm the presence of Eu3+ and Tb3+ ions. The luminescent properties of the obtained phosphors were studied in detail. Cathodoluminescence measurements indicate that the best emission intensity is for Eu3+:Tb3+ doping ratios of 80:0, 90:0 and 20:80. On the other hand, samples with 80:0, 60:40, and 20:80 doping ratios show the highest intensity in a detailed photoluminescence analysis and they exhibit the highest quantum yield values. A complete and efficient energy transfer from the sensitizer Tb3+ to the activator Eu3+ is observed in all co-doped phosphors post-annealed at 800 °C for 4 h. Thus, the Li3Ba2La3(MoO4)8:Eu3+,Tb3+ materials fabricated by combustion synthesis are excellent phosphors for being applied as red-emitting component in solid-state white-light lamps due to an improved color rendering index (CRI) that can be obtained under long UV-blue excitation wavelengths.

Cathodoluminescence of Ultrathin InAs Layers Embedded in GaAs Matrix

Ultrathin InAs layers with different thicknesses, from 0.75 to 1.4 monolayer, are grown in the GaAs matrix by molecular beam epitaxy on GaAs (001) substrates. For sub-monolayer heterostructures, islands or segregations exist during the growth process. Taking advantage of the high spatial resolution of focused electron beams, cathodoluminescence measurements obtain a smaller excitation spot than conventional photoluminescence. Based on the change on the peak position, line width, and intensity, cathodoluminescence spectra indicate that the size, geometry, and roughness develop with the InAs content. Moreover, spatial discontinuities of ultrathin InAs layers are observed on spectrum images and transmission electron microscopy images. This research reveals the correlation between the optical and structural properties of ultrathin InAs layers.

Giant Reduction in the Thermal Conductivity of Porous β-Ga2O3 with Multiple Heat-Blocking Mechanisms

In this work, multiple strategies have been adopted to suppress the lattice thermal conductivity in β-Ga2O3 by point defects, grain boundaries, secondary phases, and pores. Porous β-Ga2O3 was prepared by a convenient calcination method together with spark plasma sintering technology. Positron annihilation lifetime and cathodoluminescence measurements reveal the existence of small micropores and various vacancies in the as-sintered β-Ga2O3. Macropores with sizes on the order of hundreds of nanometers are also observed by scanning electron microscopy. Due to these pores, the as-sintered β-Ga2O3 shows a high porosity of 63.4% and possesses abundant boundaries between the solid matrix and the air. In addition, the secondary phase of ε-Ga2O3 is also revealed by X-ray diffraction. The above microstructures cause strong enhancement in phonon scattering. As a result, an extremely low thermal conductivity of 0.30 W m–1 K–1 is obtained at room temperature in the as-sintered β-Ga2O3, which is far below the amorphous limit (1.15 W m–1 K–1) and is the lowest value reported so far for β-Ga2O3. Our work provides an avenue to reduce the thermal conductivity for the β-Ga2O3 materials and is believed to be more widely applicable for many other materials.

ε-Ga2O3 thin films grown by metal-organic chemical vapor deposition and its application as solar-blind photodetectors

In this work, hetero-epitaxy of ε-Ga2O3 thin films are grown on c-plane sapphire by metal-organic chemical vapor deposition (MOCVD). Different oxygen precursors of deionized water (H2O) or high-purity nitrous oxide (N2O) gas are used and their impacts on crystal structure, optical absorption, cathodoluminescence, and photoelectric properties have been intensively studied. X-ray diffraction (XRD) analysis has shown that the ε-Ga2O3 epilayers are highly (001) oriented and the VI/III ratio is a critical growth parameter for the phase purity of Ga2O3. Cathodoluminescence (CL) measurements reveal that the luminescence peaks appear in the violet–blue–green region. A general increase of luminescence intensity is evidenced for samples grown using H2O as oxygen sources, which is explained by higher radiation recombination. Deep-ultraviolet (DUV) photodetectors with metal-semiconductor-metal (MSM) structure have been fabricated based on the ε-Ga2O3 thin films. The comparison of the device performances shows that faster response speed and higher responsivity are obtained for the device based on the ε-Ga2O3 grown by H2O as precursors, which indicates the potential of high quality ε-Ga2O3 to be applied in DUV photodetectors.

Luminescence and Raman spectroscopic properties of cubic boron nitride grown by drop-casting technique

The emission of sub-bandgap photons from a ultrawide bandgap cubic-boron nitride material is a phenomenon that can be applied to next-generation quantum photonic devices. This paper reports the structural and morphological characteristics of this new research material synthesized by the drop-casting technique in ambient conditions. Our x-ray diffraction (XRD) analysis shows a primary peak at ∼44° related to the (111) plane which confirms the cubic phase of boron nitride. The optical and vibrational properties of the material were investigated by cathodoluminescence and Raman spectroscopic measurements, respectively. The optical study provides experimental evidence of four different radiative sub-bandgap levels in the visible spectral region. These preliminary findings show a potential route to implement high-performance quantum emitters using this highly-sought material with extreme properties.

Eu3+ heavily doped tellurite glass ceramic as an efficient red phosphor for white LED

To design a phosphor for near ultraviolet (n-UV) based white light emitting diodes (wLED) with low correlated color temperature (CCT) and high CRI, a series of highly Eu3+ activated tellurite samples was prepared. Glass ceramic (GC) containing Eu2Te6O15 microcrystals were obtained as a function of crystallization time from 0 to 4 h at 435 °C. X-ray diffraction (XRD) and cathodoluminescence measurement confirm the existence Eu2Te6O15 microcrystals in translucent glass ceramic, improving the luminescence properties of the samples. Upon 393 nm excitation two intense emission bands centered at 594 nm and 614 nm were observed with an increase of 200% for the crystallized samples at 435 °C for 4 h with respect to as-fabricated glasses. Radiometric properties of heavily (10 mol %) Eu3+ doped samples as a function of crystallization time were investigated and the maximum luminous efficacy (LE) obtained is 12.01 lm/W for a crystallization time of 4 h. A green phosphor (SrBaSiO4:Eu2+) on top of samples was used the construct a white light-emitting diode and the results show that the color coordinate temperature (CCT) can be tuned from 4729 K to 3405 K as crystallization time increase from 0 to 4 h with a diminishing of LE from 34.3 to 19 lm/W. The results show that tellurite glass and GC present enormous potential as phosphor converters in solid state lighting application.

New Mechanism for Long Photo-Induced Enhanced Raman Spectroscopy in Au Nanoparticles Embedded in TiO2.

The photo-induced enhanced Raman spectroscopy (PIERS) effect is a phenomenon taking place when plasmonic nanoparticles deposited on a semiconductor are illuminated by UV light prior to Raman measurement. Results from the literature show that the PIERS effect lasts for about an hour. The proposed mechanism for this effect is the creation of oxygen vacancies in the semiconductor that would create a path for charge transfer between the analyte and the nanoparticles. However, this hypothesis has never been confirmed experimentally. Furthermore, the tested structure of the PIERS substrate has always been composed of plasmonic nanoparticles deposited on top of the semiconductor. Here, gold nanoparticles co-deposited with porous TiO2 are used as a PIERS substrate. The deposition process confers the nanoparticles a unique position half buried in the nanoporous semiconductor. The resulting PIERS intensity is among the highest measured until now but most importantly the duration of the effect is significantly longer (at least 8 days). Cathodoluminescence measurements on these samples show that two distinct mechanisms are at stake for co-deposited and drop-casted gold nanoparticles. The oxygen vacancies hypothesis tends to be confirmed for the latter, but the narrowing of the depletion zone explains the long PIERS effect.

Non-invasive and non-destructive characterization of MBE-grown CdZnTe/CdTe superlattice-based dislocation filtering layers

We report on the structural and optical properties of heteroepitaxial II–VI CdTe (211)B buffer layers with strained CdZnTe/CdTe superlattice layers, investigated by employing non-destructive methods including high-resolution x-ray diffraction, cathodoluminescence, and photoluminescence spectroscopy. X-ray diffraction reciprocal space mapping measurements revealed that the superlattice layers are coherently strained, leading to a spread in x-ray double-crystal rocking curve full-width at half-maximum values but better in-plane lattice-matching with HgCdTe. Both cross-sectional cathodoluminescence and photoluminescence measurements confirm the coherent growth of superlattice layers and their dislocation filtering effects. Both these techniques in CdTe layers are found to be well correlated with the dislocation density as determined by etch pit density measurements. The results indicate the potential of these non-destructive methods to be further developed into general-purpose techniques capable of characterizing the defect evolution in semiconductor heteroepitaxy.

From the synthesis of hBN crystals to their use as nanosheets in van der Waals heterostructures

In the wide world of 2D materials, hexagonal boron nitride (hBN) holds a special place due to its excellent characteristics. In addition to its thermal, chemical and mechanical stability, hBN demonstrates high thermal conductivity, low compressibility, and wide band gap around 6 eV, making it a promising candidate for many groundbreaking applications and more specifically in van der Waals heterostructures. Millimeters scale hBN crystals are obtained through a disruptive dual method (polymer derived ceramics (PDC)/pressure-controlled sintering (PCS)) consisting in a complementary coupling of the PDC route and a PCS process. In addition to their excellent chemical and crystalline quality, these crystals exhibit a free exciton lifetime of 0.43 ns, as determined by time-resolved cathodoluminescence measurements, confirming their interesting optical properties. To go further in applicative fields, hBN crystals are then exfoliated, and resulting boron nitride nanosheets (BNNSs) are used to encapsulate transition metal dichalcogenides (TMDs). Such van der Waals heterostructures are tested by optical spectroscopy. BNNSs do not luminesce in the emission spectral range of TMDs and the photoluminescence width of the exciton at 4 K is in the range 2–3 meV. All these results demonstrate that these BNNSs are of high quality and relevant for future opto-electronic applications.

Effects of Defect Density on Optical Properties Using Correlative Cathodoluminescence and Transmission Electron Microscopy Measurements on Identical PrNbO4Particles

Understanding the optical properties of lanthanide niobates is essential to improve the development of these materials. In this study, we investigated PrNbO4 powder particles with different density of twins which influences the intensity of the emission lines. The twins form during synthesis of these particles based on a solid-state route. A correlative approach using backscattered electron imaging, cathodoluminescence measurements, focused ion beam lift out, and aberration-corrected transmission electron microscopy was used at the same location within the particles. Emission lines were acquired by using a cathodoluminescence spectrometer attached to a scanning electron microscope on two regions including twinned and twin free areas. The results were compared and indicate that the areas with higher density of twins have more intense emission lines. The reason for the improved luminescent properties is the perturbation of the energy states caused by the defects which promotes the occurrence of the parity forbidden f–f transitions.

Correlating yellow and blue luminescence with carbon doping in GaN

Blue and yellow emission bands in carbon-doped GaN grown by MBE were investigated in low-temperature cathodoluminescence measurements performed in a scanning transmission electron microscope (STEM-CL) with high spatial resolution. Blue luminescence at 2.85 eV and two contributions in the spectral range of the yellow emission band around 2.2 eV separated by 120 meV are observed in carbon-doped material, whereas only one distinctive yellow luminescence contribution was found in unintentionally-doped GaN.