Electroluminescence Spectra Research Articles

Luminescence properties of Cr3+-doped Al6Ge2O13 broadband near-infrared phosphor

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are gaining attention as new solid-state light sources for food safety and health monitoring. Herein, a series of Cr3+-doped Al6Ge2O13 (AGO) NIR phosphors were obtained by the high-temperature solid state reaction. The photoluminescence (PL) excitation spectrum of AGO:Cr3+ shows a strong broadband absorption in the 400–500 nm region, which corresponds well to the blue light chip. The phosphor's PL emission spectrum exhibits a broadband spanning 600–1000 nm. The integrated emission intensity of AGO:3%Cr3+ at 420 K can keep 81% of that at 300 K, demonstrating good luminous thermal stability. The near-infrared output power of pc-LED device integrating AGO:Cr3+ phosphor with a 430 nm blue light chip reaches 81.7 mW at 300 mA. The device's electroluminescence spectrum displays a broadband centered at 780 nm, with a full width at half maximum (FWHM) of 160 nm. These findings could drive the development of NIR pc-LED light sources for miniaturized near-infrared spectrometers.

Novel deep‐red‐emitting double‐perovskite type Ca2ScNbO6:Mn4+ phosphor: Structure, spectral study, and improvement by NaF flux

AbstractA novel deep‐red‐emitting phosphor Ca2ScNbO6:Mn4+ is prepared via a high‐temperature solid‐state reaction and its luminescent properties are systematically investigated. The results show that Mn4+‐activated Ca2ScNbO6 phosphors have broad absorption in ultraviolet region, and show bright deep‐red emission at 692 nm. The optimal doping concentration, crystal‐field strength, internal quantum efficiency, and mechanism of concentration and thermal quenching effects are discussed in detail. Moreover, NaF flux is screened out to improve both luminescent intensity and morphology of the phosphor. Finally, a red light‐emitting diode (LED) lamp is fabricated with as‐prepared Ca2ScNbO6:Mn4+ phosphors and a 365 nm LED chip. The electroluminescence spectra show a good overlapping with phytochrome PR and PFR absorbance. The results provided the as‐synthesized Ca2ScNbO6:Mn4+ phosphors a great potential in plant growth lighting.

Effects of polarized-induced doping and graded composition in an advanced multiple quantum well InGaN/GaN UV-LED for enhanced light technology

In this paper, a light-emitting diode in the ultra-violet range (UV-LED) with multiple-quantum wells (MQWs) of InGaN/GaN is designed and analyzed through Technology Computer-Aided Design (TCAD) simulations. The polarization effects in III-nitride heterojunction and the effects of graded composition in the electron blocking layer (EBL) are exploited to enhance the performance of the proposed UV-LED. It is observed that the effect of graded composition in the EBL helps to enhance the electrical and optical performance of the LED, thereby enabling the achievement of some promising results. The simulation-based results demonstrated that superior internal efficiency and an inferior leakage current are achieved by using a graded Al composition in the EBL rather than a uniform composition. The reported results also confirm the remarkable improvement of the light output power by 17% at ∼100 mA when using the graded composition and also show a reduction in series resistance leading to more current. Graded Al composition in the EBL results in the enhancement of electroluminescence spectra (i.e., an increase in the peak of the spectral density).

Creation of effective sources of white radiation based on GaP(As,N) on silicon substrates

The article is devoted to the study of light-emitting heterostructures based on GaP(As,N) dilute nitrides, monolithically grown on silicon substrates by plasma-assisted molecular beam epitaxy. Current-voltage characteristics and electroluminescence spectra of the grown heterostructures are obtained. For the first time, a unique effect is observed in GaP(As,N) dilute nitrides - the appearance of white electroluminescence when a reverse bias is applied. The result was obtained due to the original design of the light-emitting heterostructure and the unique properties of dilute nitride solid solutions.

Three-color white electroluminescence emission using perovskite quantum dots and organic emitters

To realize a full-color display in the research field of perovskites or perovskite-structured quantum dots (PeQDs), the development of white-light-emitting devices that operate by emitting light of three primary colors (red, green, and blue) has emerged as an active research topic. In the present study, we report for the first time three-color white-light emission with high brightness from white-emitting PeQD organic light-emitting diodes (WPeQD-OLEDs) fabricated using a PeQD material and organic emitters. A WPeQD-OLED bilayer was prepared by depositing a blue-emitting organic layer on top of a CsPb(Br/I)3 QD layer mixed with N9,N10-Bis(4-(tert-butyl)phenyl)-N9,N10-Di-o-Tolylanthracene-9,10-Diamine (p-Tb-o-Me-TAD), which were spin-coated as red and green emitters, respectively. The WPeQD-OLED device was stable during operation and demonstrated emission of three primary colors. In the WPeQD-OLED device, charge carriers were distributed by an 9-(naphthalen-1-yl)-10-(naphthalen-2-yl)anthracene (α,β-ADN) blue-emitting host material with a deep highest occupied molecular orbital level. The electroluminescence (EL) spectra of the WPeQD-OLEDs showed EL maximum peaks at 460, 527, and 640 nm; the CIE color coordinates of the emitted light were (0.33, 0.40). The EL results confirmed that the maximum luminance was 49,000 cd m−2 and the maximum luminance efficiency and power efficiency were 4.48 cd A−1 and 2.16 lm W−1, respectively.

Explorations on Growth of Blue-Green-Yellow-Red InGaN Quantum Dots by Plasma-Assisted Molecular Beam Epitaxy.

Self-assembled growth of blue-green-yellow-red InGaN quantum dots (QDs) on GaN templates using plasma-assisted molecular beam epitaxy were investigated. We concluded that growth conditions, including small N2 flow and high growth temperature are beneficial to the formation of InGaN QDs and improve the crystal quality. The lower In/Ga flux ratio and lower growth temperature are favorable for the formation of QDs of long emission wavelength. Moreover, the nitrogen modulation epitaxy method can extend the wavelength of QDs from green to red. As a result, visible light emissions from 460 nm to 622 nm have been achieved. Furthermore, a 505 nm green light-emitting diode (LED) based on InGaN/GaN MQDs was prepared. The LED has a low external quantum efficiency of 0.14% and shows an efficiency droop with increasing injection current. However, electroluminescence spectra exhibited a strong wavelength stability, with a negligible shift of less than 1.0 nm as injection current density increased from 8 A/cm2 to 160 A/cm2, owing to the screening of polarization-related electric field in QDs.

High-Performance Blue Quasi-2D Perovskite Light-Emitting Diodes via Balanced Carrier Confinement and Transfer

HighlightsA new concept to optimize the passivating agents for the balance of the carrier confinement and transfer in blue quasi-2D perovskites.The moderate tributylphosphine oxide is introduced into the quasi-2D perovskites to simultaneously strengthen the carrier confinement for massive radiative recombination as well as promote efficient carrier transfer in the quasi-2D perovskites.High-efficient and stable blue PeLEDs are achieved with an external quantum efficiency of 11.5% and a very long operational stability of 41.1 min without any shift of the electroluminescence spectra.

Efficient Ultraviolet Organic Light-Emitting Diodes with a CIEy of 0.04 and Negligible-Efficiency Roll-Off.

Organic light-emitting diodes (OLEDs) with ultraviolet (UV) emission (λEL ≤ 400 nm) have attracted special attention in commercial and civil fields owing to their special functions. Nevertheless, the lack of high-quality ultraviolet emitters restricts the practical application of UV OLEDs. Herein, a novel organic molecule with desirable UV emission, 2Na-CzCN, is developed for UV OLEDs. Theoretical investigation indicates that it is equipped with hybridized local and charge-transfer (HLCT) characteristics, which is in favor of the high-lying reverse intersystem crossing (RISC) process, thus remarkably boosting the exciton utilization in electroluminescence (EL). Significantly, the nondoped device derived from the 2Na-CzCN emitter exhibits an EL emission peak of 398 nm with a maximum external quantum efficiency (EQE) of 5.92%, which represents the record-high result among nondoped UV OLEDs. The doped UV OLED of 2Na-CzCN radiates robust UV emission at a peak of 392 nm with a maximum EQE of 6.15%. Coupled with the narrow full width at half-maximum (FWHM) of the EL spectra, desirable color purities with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.06) and (0.16, 0.04) for nondoped and doped OLEDs are presented, respectively. Additionally, the potential of 2Na-CzCN adopted as the host material is demonstrated with phosphorescent OLEDs (PhOLEDs), and all of the devices show good EL performances with low-efficiency roll-offs. An orange PhOLED with 2Na-CzCN acquires a maximum current and external quantum efficiency of 84.9 cd A-1 and 25.3%, respectively. These findings may pave an avenue for the development of high-performance UV emitters.

Role of Guest Materials in the Lower Stability of Solution-Coated versus Vacuum-Deposited Phosphorescent OLEDs.

Utilizing different phosphorescent materials as emitter guests, this work investigates the root causes of the lower electroluminescence (EL) stability of solution-coated (SOL) organic light-emitting devices (OLEDs) relative to their vacuum-deposited (VAC) counterparts. The results show that emitter guest molecules aggregate under electrical stress, leading to the emergence of new longer-wavelength bands in the EL spectra of the devices over time. However, the intensity of these aggregation emission bands is much stronger in the case of SOL host:guest systems than that of their VAC counterparts, indicating that guest aggregation occurs much faster in the former. The results reveal that the phenomenon arises from differences in the initial morphologies and are likely associated with the use of solvents in the solution-coating process. Moreover, although excitons can drive this aggregation in the case of SOL emissive layer (EML) devices, the coexistence of excitons and polarons accelerates this phenomenon significantly. The results uncover one of the main causes of the lower stability of OLEDs made by solution coating and reveal the importance of adopting new molecular designs that make them less susceptible to aggregation for the development of SOL OLEDs with high performance.

Enhanced luminescence properties of Li2MgTiO4: Mn4+, Ge4+ phosphor via single cation substitution for indoor plant cultivation

Red and far-red emitting phosphors have been widely used in phosphor-converted light emitting diode (pc-LED) devices to provide lighting for indoor plant growth, thus achieving desired product qualities. Among the many ways to optimize phosphors’ optical performance, cationic substitution is one of the most effective methods. In this study, red phosphors (Li 2 MgTi 1- x - y O 4 : x Mn 4+ , y Ge 4+ ) were synthesized by high temperature solid state method and the optical performance of phosphors were improved with increasing Ge 4+ constituents. In particular, luminescence intensity of Li 2 MgTiO 4 : 0.002Mn 4+ , 0.1Ge 4+ increased by 152% under 468 nm excitation, and the thermostability of emission intensity increases from 22% ( y = 0) to 43% ( y = 0.1), which is about twice as much. Finally, pc-LED device was fabricated via the red phosphor Li 2 MgTiO 4 : 0.002Mn 4+ ,0.1Ge 4+ coated on a 470 nm ultraviolet chip. By changing the proportion of the phosphor, the electroluminescence spectra of pc-LED device could match well with the absorption regions of plant pigments. Therefore, Li 2 MgTiO 4 : 0.002Mn 4+ , 0.1Ge 4+ phosphor has potential application in plant lighting. Furthermore, this work can offer some helpful references for improving luminescent efficiency by simply modulating the chemical composition. The luminescence intensity of Li 2 MgTiO 4 : 0.002Mn 4+ , 0.1Ge 4+ increased by 152%. The thermostability of emission intensity increases from 22% ( y = 0) to 43% ( y = 0.1), which is about twice as much. Finally, the pc-LED device could emit bright blue and red light, which matched with the absorption regions of plant pigments well.

Method for studying the photostability of solar cells based on organic-inorganic perovskites using a confocal spectrometer

A method for studying photosensitive structures using the example of studying the photodegradation and dark recovery of organic-inorganic perovskite solar cells is present. The method is based on the use of a confocal spectrometer to measure Raman spectra, photo- and electroluminescence spectra and kinetics, the kinetics of the short-circuit current and the open-circuit voltage under local exposure to monochromatic radiation. Raman spectra make it possible to establish the presence or absence of secondary phases, the formation of which is possible in photosensitive layers under the influence of light. The photoluminescence spectra enable to reveal the single-phase nature of the object under study. Mapping the intensity and position of the center of mass of the photoluminescence band in the plane of the object makes it possible to judge the spatial arrangement of the centers of non-radiative recombination of charge carriers, the distribution of the regions with the highest and lowest efficiency of the extraction of charge carriers by transport-acceptor layers and the spatial homogeneity of the chemical composition. Comparison of the electroluminescence spectra before and after light exposure allows revealing the formation of non-radiative recombination centers in the photoabsorbing layer and at interfaces with the transport layers. Analysis of the kinetics of changes in the parameters of the photoluminescence band obtained by measuring the short-circuit current and the open-circuit voltage makes it possible to establish the dominant photoinduced processes leading to a change in the intensity of the photoluminescence band.

White light emitting diodes based on green graphene quantum dots and red graphene quantum dots

White light emitting diodes (WLEDs) have attracted the attention of numerous scholars because of its high photoelectric conversion efficiency, low energy consumption and high reliability. They are known as the new generation of lighting energy in the twenty first century. Currently, the most common WLEDs are combined by blue LED chip and ce-doped yttrium aluminum garnet (YAG: Ce3+) yellow phosphors. The advantages are simple production, low cost and high luminous efficiency. However, WLEDs made of blue LED chip and yellow phosphors lacks red spectrum and exhibits luminescence, and its color rendering index (CRI) is low, usually only 70. At the same time, quantum dots (QDs) are considered to be the most potential materials for WLEDs color conversion layers due to their wide excitation spectrum, narrow emission spectrum, adjustable band gap and high quantum yield. In this paper, we fabricated green graphene QDs (GQDs) and red GQDs, measured and analyzed their morphology, structure and photoluminescence. The green GQDs, red GQDs and yellow phosphors were used to fabricate the WLEDs. The produced WLEDs showed excellent optical performance and working performance, among which Commission International de L 'Eclairage (CIE) chromaticity coordinates are (0.3332, 0.3359), and the correlated color temperature (CCT) is 5464 K (driving current is 30 mA). Electroluminescence (EL) spectra of the device at different currents were also measured.

Silicon Light-Emitting Diodes with Dislocation-Related Luminescence Fabricated with Participation of Oxygen Precipitates

Silicon light-emitting diodes with dislocation-related electroluminescence have been studied at room temperature. For the fabrication of the light-emitting diode structures, a well-known method for the formation of dislocation-related luminescence centers during anneals of silicon with a high oxygen concentration in a flow of argon was modified by introducing a preliminary O+ ion implantation and carrying out a final anneal in a chlorine-containing atmosphere. In the electroluminescence spectra, the D1 dislocation-related luminescence line dominates at currents less than <150 mA and the near-band-edge luminescence line starts to dominate with increasing current. The electroluminescence excitation efficiency for the D1 center is 3.3·10-20 cm2·s at room temperature. Keywords:: Light-emitting diodes, dislocation-related luminescence, silicon, oxygen precipitates.

Стимулированное излучение в гетероструктурах InAs/InAsSb/InAsSbP с асимметричным электронным ограничением

The electroluminescent characteristics of the InAs/InAs1−ySby /InAsSbP asymmetric light-emitting diode heterostructures with high InSb mole fraction in the active region (y > 0.09) in the temperature range 4.2−300 K have been studied. Stimulated emission was achieved in the wavelength range 4.1−4.2 μm at low temperatures (T < 30 K). It was found that the electroluminescence spectra were formed as a result of the superposition of contributions from different channels of radiative recombination of charge carriers near the type II heterointerface. The effect of the quality of the type II InAsSb/InAsSbP heterojunction on the radiative interface transitions with an increase in the content of InSb in the ternary solid solution is considered.

Study of active regions based on multiperiod GaAsN/InAs superlattice

The results of a study of nitrogen-containing active regions based on superlattices grown on GaAs substrates are presented. Active regions based on alternating InAs and GaAsN layers were fabricated by molecular-beam epitaxy using a nitrogen plasma source. Based on the XRD analysis, the thicknesses and average composition of superlattice layers are estimated. The study of dark-field images obtained by transmission electron microscopy showed the presence of interdiffusion of InAs into GaAsN. The results of a study of the photoluminescence and electroluminescence spectra at different pump levels are presented. Efficient electroluminescence is demonstrated near 1150 nm with a full width at half-maximum of about ~90 meV. Keywords: Superlattices, molecular beam epitaxy, gallium arsenide, dilute nitride, GaAsN, InAs.

Кремниевые светодиоды с дислокационной люминесценцией, сформированные с участием кислородных преципитатов

Silicon light-emitting diodes with dislocation-related electroluminescence have been studied at room temperature. For the fabrication of the light-emitting diode structures, a well-known method for the formation of dislocation-related luminescence centers during anneals of silicon with a high oxygen concentration in a flow of argon was modified by introducing a preliminary O+- ion implantation and carrying out a final anneal in a chlorine-containing atmosphere. In the electroluminescence spectra, the D1 dislocation-related luminescence line dominates at currents less than 150 mA and the near-band-edge luminescence line starts to dominate with increasing current. The electroluminescence excitation efficiency for the D1 center is 3.3 · 10-20 cm2 · s at room temperature.

Stimulated emission in the InAs/InAsSb/InAsSbP heterostructures with asymmetric electronic confinement

The electroluminescent characteristics of the InAs/InAs1-ySby/InAsSbP asymmetric light-emitting diode heterostructures with high InSb mole fraction in the active region (y>0.09) in the temperature range 4.2-300 K have been studied. Stimulated emission was achieved in the wavelength range 4.1-4.2 μm at low temperatures (T<30 K). It was found that the electroluminescence spectra were formed as a result of the superposition of contributions from different channels of radiative recombination of charge carriers near the type II heterointerface. The effect of the quality of the type II InAsSb/InAsSbP heterojunction on the radiative interface transitions with an increase in the content of InSb in the ternary solid solution is considered. Keywords: heterojunctions, InAs, antimonides, electroluminescence, light-emitting diodes.

Исследование активных областей на основе многопериодных сверхрешеток GaAsN/InAs

The results of a study of nitrogen-containing active regions based on superlattices grown on GaAs substrates are presented. Active regions based on alternating InAs and GaAsN layers were fabricated by molecular−beam epitaxy using a nitrogen plasma source. Based on the XRD analysis, the thicknesses and average composition of superlattice layers are estimated. The study of dark-field images obtained by transmission electron microscopy showed the presence of interdiffusion of InAs into GaAsN. The results of a study of the photoluminescence and electroluminescence spectra at different pump levels are presented. Efficient electroluminescence is demonstrated near 1150 nm with a full width at half-maximum of about 90 meV.

Polarization Properties of InGaN Vertical-Cavity Surface-Emitting Laser With Pipe Distributed Bragg Reflector

Indium gallium nitride (InGaN) vertical-cavity surface-emitting lasers (VCSELs) with top dielectric and bottom pipe-gallium nitride (GaN) distributed Bragg reflectors (DBRs) were demonstrated. Pipe-GaN DBR structure consisted of a lateral wet-etched pipe-GaN layer and a GaN layer in the 20 pair stack structure as an embedded reflector. The optical birefringence behavior of the anisotropic pipe-GaN structure induced the polarization properties in the reflectance and electroluminescence (EL) spectra. Polarization EL emission peaks with narrow line-widths were measured at 430.8 nm (perpendicular to pipe-GaN) and 432.5 nm (along with pipe-GaN), respectively. The EL emission peaks with high polarization ratios were observed due to the short resonance cavity effect with the birefringence pipe-GaN DBR structure.

Electroluminescence analysis of silicon interdigitated back contact solar cells with a front surface selective band offset barrier

Electroluminescence allows rapid characterization of an entire photovoltaic solar cell and visualization of defects at the micrometer scale. Here we focus on the optoelectronic properties of silicon interdigitated back contact cells characterized by electroluminescence. The spatially resolved electroluminescence helps us control the quality of interdigitated back contact structures used in silicon bottom subcells in a three-terminal tandem perovskite on silicon solar cell. Local variations in minority carrier diffusion length, surface recombination velocity and, the impact of resistive and optical losses were analyzed by electroluminescence mapping. In addition, we quantify the radiative saturation current density and the radiative open circuit voltage using the electroluminescence spectrum of the cell. This step allows us to accurately assess the performance limits induced in the device due to the non-radiative recombination.