Phosphor Layer Research Articles

Field-emission electron gun for a MEMS electron microscope

This article presents a field-emission electron gun intended for use in a MEMS (microelectromechanical system) electron microscope. Its fabrication process follows the technology of a miniature device under development built from silicon electrodes and glass spacers. The electron gun contains a silicon cathode with a single very sharp protrusion and a bundle of disordered CNTs deposited on its end (called a sharp silicon/CNT cathode). It was tested in diode and triode configurations. For the diode configuration, a low threshold voltage <1000 V and a high emission current that reached 90 µA were obtained. After 30 min of operation at 900 V, the emission current decreased to 1.6 µA and was stable for at least 40 min, with RMS fluctuation in the anode current lower than 10%. The electron beam spot of the source was observed on the phosphor screen. In the diode configuration, the spot size was the same as the emission area (~10 µm), which is a satisfactory result. In the triode configuration, an extraction electrode (gate) control function was reported. The gate limited the emission current and elongated the lifetime of the gun when the current limit was set. Moreover, the electron beam current fluctuations at the anode could be reduced to ~1% by using a feedback loop circuit that controls the gate voltage, regulating the anode current. The developed sharp silicon/CNT cathodes were used to test the MEMS electron source demonstrator, a key component of the MEMS electron microscope, operating under atmospheric pressure conditions. Cathodoluminescence of the phosphor layer (ZnS:Ag) deposited on the thin silicon nitride membrane (anode) was observed.

Europium‐doped barium chloride storage phosphor plate synthesized by pulsed laser deposition

AbstractIn computed radiography, scattering of the stimulation light by the storage phosphor crystals in the imaging plates negatively impacts spatial resolution. Storage phosphor plates with thinner phosphor layers have been developed to reduce scattering distance and increase spatial resolution, although at the expense of reduced x‐ray absorption. The authors hypothesize that a transparent or translucent nanostructured film, containing a much higher percentage of storage phosphor crystals than achievable in bulk glass‐ceramic materials made by conventional methods, may have acceptable photostimulated luminescence efficiency and imaging performance characteristics greater than commercial imaging plates. Films were produced via pulsed laser deposition by alternating target materials of the storage phosphor BaCl2:Eu2+ and either silica or silicon. X‐ray diffraction and photoluminescence characterization were conducted to confirm the presence of BaCl2:Eu2+ crystallites. The films were able to store optical data and be read out to produce x‐ray radiographs demonstrating 50‐µm spatial resolution. The performance of the experimental storage phosphor plates was compared to commercially available imaging plates. The authors demonstrate for the first time the synthesis of a glass‐ceramic imaging plate for computed radiography by pulsed laser deposition.

Shungite Carbon Nanoparticles as Modifiers of Zns:Cu Phosphor, Based on Analysis of the EPR Spectral Lines of Mn&lt;sup&gt;+2&lt;/sup&gt;

Water dispersions of shungite carbon (ShC) nanoparticles were used for modifying the particle surface of ZnS:Cu, commercial electrophosphor. The EPR spectrum of ZnS:Cu powder has parameters consistent with the paramagnetic centers of Mn+2. Modifying the phodphor surface with ShC nanoparticles results in a non-monotonic change in line width, amplitude and integral intensity caused by nanoparticle concentration, which correlates with variations in the brightness of electroluminescence. Variations in the parameters of spectral lines with nanoparticle concentration and UHF saturation power are interpreted in terms of modification and creation of additional dislocations in the subsurface layer of phosphor with new physico-chemical properties.

Color-Tunable White LEDs with Single Chip Realized through Phosphor Pattern and Thermal-Modulating Optical Film.

In this paper, a new method to regulate the correlated color temperature (CCT) of white light-emitting diodes (LEDs) is proposed for the single-chip packaging structure, in which the blue light distribution emitted from the chip in the red/yellow phosphor layer was modulated through changing the paraffin-polydimethylsiloxane (PDMS) film transparence and haze. The results show that the transmittance of the paraffin-PDMS film can be modulated from 49.76% to 97.64%, while the haze of that ranges from 88.19% to 63.10%. When the thickness of paraffin-PDMS film is 0.6 mm, and the paraffin-PDMS film concentration is 30 wt%, the CCT of white LED decreases from 15177 K to 3615 K with the increase of thermal load in the paraffin-PDMS film. The modulating range of its CCT reaches 11562 K. The maximum CCT variation at the same test condition is only 536 K in the repeated experiments within one week.

Monitoring the health of laser-driven phosphor-converted white light source using spectral interference technique

We report an innovative method for early monitoring of the Opto-thermal health of laser-driven phosphor-converted white light source using low coherence spectral interference technique. A phosphor layer was irradiated using a high-power laser source in reflection mode and the broadband light generated from the phosphor layer was made incident onto a common path interferometer. The interferometer was made of two optically flat glass plates stacked together with minimum optical path difference between the two reflecting components (≤ 1µm). The constructive and destructive interference peaks were recorded in the spectrum. A significant change in Stokes shift was observed from spectral interference peak shifts in a short interval of time and this helped in analyzing the phosphor Opto-thermal behaviour from thermal initialization to the material saturation. The minimization of the observed changes in the Stokes shift can be helpful in the material development process for thermally stable illumination.

The application of dual-layer remote phosphor geometry in achieving higher color quality of WLEDs

If remote phosphor structures are put into comparison with conformal phosphor or in-cup phosphor, their luminous flux are better, but the color quality is not as elevated. This leads to an obvious need of a practical solution to enhance color quality. Therefore, many studies were carried out to achieve this purpose, and so is ours. We proposed using two layers of phosphor in WLEDs to achieve better rendering ability and chromatic performance. The identical WLEDs with different color temperatures, 5600 K-8500 K, were used and reported in this paper. Our research consists of two parts, which are placing a layer of red phosphor Sr w F x B y O z :Eu 2+ ,Sm 2+ on the yellow YAG:Ce 3+ phosphor layer at first, and then specifying an appropriate Sr w F x B y O z :Eu 2+ ,Sm 2+ concentration to reach the highest color performance. It is shown that with the contribution of Sr w F x B y O z :Eu 2+ ,Sm 2+ ,the color rendering index (CRI) and color quality scale (CQS) are increased. This can be explained by the increased amount of red light components in the WLEDs when the concentration of Sr w F x B y O z :Eu 2+ ,Sm 2+ was greater. However, excessive Sr w F x B y O z :Eu 2+ ,Sm 2+ will cause the reduction in the flux, which has been proven by the application of Mie scattering and the Lambert-Beer law. Therefore, the conclusion will present an optimal amount of Sr w F x B y O z :Eu 2+ ,Sm 2+ to obtain high color quality while minimizing the light loss.

Effects of BaSO&lt;sub&gt;4&lt;/sub&gt; nano-particles on the enhancement of the optical performance of white LEDs

The usage of BaSO 4 nanoparticles on WLEDs luminous flux and color uniformity improvements have been analyzed and demonstrated in this manuscript. The mixture of BaSO 4 and silicone placed on the yellow phosphor layer benefits the internal light scattering and thus enhances the angular correlated color temperature (CCT) homogeneity. Specifically, the blue-light intensity at large angles tend to increase and results in light intensity discrepancy, which can be corrected with added BaSO 4 . In addition to this, the BaSO 4 -silicone composite modifies the refractive index of the air-phosphor layer interface to an appropriate value, and thus, the luminous efficiency increases. The results show that the CCT deviations is reduced by 580 K, from 1000 K to 420 K, within the angle range from -70 0 to +70 0 with BaSO 4 in the phosphor structure. The increase in luminous flux is also recorded by 2.25%, in comparison with that of the non-BaSO 4 traditional structure, at the 120-mA driving current. Hence, integrating BaSO 4 nanoparticles into the remote phosphor structure can contributes to the enhancement of both lumen output and CCT uniformity.

Study of crystallization kinetics, microstructure and optical properties of Ce: YAG glass-ceramics for white LED applications

CeO2 doped Y2O3-Al2O3-SiO2 (YAS) glass composition was synthesized and devitrified to a single phase Ce: YAG glass–ceramics phosphor with controlled heat treatment process. Kinetic predictions for crystallization of the glass were derived from isoconversional analysis of DTA data using AKTS software. Activation energy of crystallization (E) at reaction progress (α = 0.5) estimated 659 kJ mol−1. The kinetic parameters were calculated as n = m = 2, representing two-dimensional nucleation and crystal growth with constant number of surface nuclei in this glass composition. From microstructure analysis of glass–ceramics we have seen the dendritic growth of crystals in the glass matrix originating from the surface creating a glass–ceramics phosphor layer of ~ 50 μm thick. No nucleation or crystal growth observed in the glass beyond 50 μm depth. Surface roughness found to increase the nucleation and accelerate the crystallization in the glass–ceramics layer. Five glass–ceramics samples prepared with increasing isothermal holding time and their photoluminescence spectra obtained by excitation with a blue LED light source. Intensity of broad band yellow emission increased with the increase in holding time which enhances the amount of Ce: YAG crystalline phase in glass–ceramics. A device was assembled for the demonstration of white light generation using an optimized glass–ceramics phosphor and blue LED in tandem.

Design, Simulation, and Reliability for LED Mobile Flash Based on Illuminance Homogeneity, Angular Color Uniformity, and Color Stability

To improve the performance of Flash LED for obtaining good picture quality, a novel ceramic packaging structure was designed and optimized based on illuminance homogeneity and angular color uniformity (ACU) for meeting the requirement of mobile flash products. The illuminance homogeneity was analyzed via both near-field optical measurement and optical simulation by Monte-Carlo method according to nine dots measurement method. Their results matched well. The target package includes vertical chip, Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrate, phosphor conformal coating layer, and silicone molding as encapsulation. Through the layer print approach and layer transfer method, the thickness of phosphors layer was optimized by finite element analysis method to improve the temperature distribution and eventually the reliability of LED units. In addition, good Delta CCT was obtained by optimizing the phosphor layer. The design methods were characterized by electrical-optical testing.

Controlling Phosphor Particle Distribution for High-Angular-Color-Uniformity and Low-Cost LEDs Based on Thermalcapillary Flow

Low cost and high performance are the pursuing goals of the light-emitting diode (LED) packaging. The phosphor layer configuration of LEDs significantly influences optical performances. In this study, thermalcapillary flow was introduced in the phosphor coating by the blue laser local irradiation. It has been demonstrated to successfully manipulate the phosphor particle distributions. In the phosphor dispensing coating, a centripetally concentrated particle distribution was realized and resulted in high angular color uniformity (ACU) and low-cost manufacture. Its angular correlated color temperature (CCT) deviation was reduced by more than 65%, compared to the traditional phosphor dispensing coating. Besides, the phosphor amount is saved by about 12%. The mechanism of ACU enhancement is analyzed. The realized phosphor particle distribution can inspire further development of the optimized phosphor layer configuration.

The Application of Mg2TiO4:Mn4+ and NaYF4:Er3+;Yb3+ and Double Convex Structure in Improving Optical Performance of Phosphor-in-Glass Based White Light-Emitting Diodes

Improving lighting performance of WLEDs, especially the color quality, has always been a priority in lighting researches. Recently, the conventional remote phosphor configuration is unable to fulfill the needs of the modern lighting market, particularly the high color expression demand has inspired the search for a novel manufacturing procedure. In this study, based on the results from previous studies, the struggles in enhancing lighting performances are pointed out, and a solution, the dual-layer remote phosphor, is proposed from our conducted experiments. Through experiments with NaYF4:Er3+;Yb3+ and Mg2TiO4:Mn4+ phosphors, the dual-layer phosphor is proven to be effective in improving lighting properties such as color rendering index (CRI) and color quality scale (CQS). The research method involves structuring and experimenting with the phosphor configuration of the yellow phosphor YAG:Ce3+ layer with a green NaYF4:Er3+;Yb3+ or a red Mg2TiO4:Mn4+ phosphor layer whose phosphor concentrations are varied. The results show that the red phosphor Mg2TiO4:Mn4+ particles benefit the CRI and CQS because the values of CRI and CQS increase with red phosphor Mg2TiO4:Mn4+ concentration. On the other hand, the green phosphor NaYF4:Er3+;Yb3+ is inferior in improving CRI and CQS but exhibits better luminous flux. Despite being useful in enhancing lighting performance, the phosphor concentration must be kept below a certain level, which will be mentioned in the article, to prevent damages. These results are verified using Mie scattering theory and Lambert-Beer's law and can be utilized in producing WLEDs with high lighting quality. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

Tailoring Particle Distribution for White LEDs With High Color-Uniformity by Selective Curing

The phosphor layer determines optical performances of phosphor-converted white light-emitting diodes (WLEDs). In this letter, a new method to control phosphor particle spatial distributions is proposed. Using blue laser irradiation, phosphor gel was selectively and rapidly cured. In the cured phosphor gel, phosphor particles were fixed. The sedimentation occurred in uncured phosphor gel to form particle patterns. With such a method, a kind of remote-conformal-combined particle distribution was obtained. It has been demonstrated that this phosphor layer configuration can result in the high-angular-color-uniformity LED packaging with different average correlated color temperatures (CCT). Compared to the dispensing coating and settling coating, the presented selective curing coating reduces the angular CCT difference by more than 74% and realizes the minimum CCT difference of 184K in the viewing angles ranging from −70° to 70°. Besides, it has no impact on the light intensity distribution. The Pearson correlation coefficients between the light intensity distributions of the selective curing coating with those of the others are larger than 0.999.

Improving optical properties of remote phosphor LED using green Y2O3:Ho3+ and red Mg4(F)(Ge, Sn)O6:Mn2+ layers

The lighting device that employs diodes to create white light (WLEDs) with quantum dots (QDs) and phosphor layers is a promising lighting method that is increasingly used in many fields on account of the remarkable color expressing ability. The QDs film is usually placed apart from the phosphor layer according to the packaging configuration to prevent light loss due to backscattering as well as preserve the consistency of the ligands on the QDs surface. The article also conducted experiments to compare the lighting properties and thermal output of the two packaging orders of QDs and phosphor. The heat discharing ranges were simulated with thermography technology, moreover, other parameters such as light energy emission and PL spectra are acquired to evaluate the efficiency of the packaging order. The results from the practical experiment show that while under 10% wt., the luminous output (LO) of green QDs-on-phosphor structure reaches 1130 lm, higher than the red QDs-on-phosphor structure with 878 lm, and the color rendering value in the configuration with red QDs on phosphor is Ra = 74 are higher than Ra = 68 index of the green QDs-on-phosphor structure. As a result, the QDs-on-phosphor is determined as the better packaging configuration to choose to achieve an overall improvement in lighting efficiency, color rendering index

Enhance the chromatic uniformity and luminous efficiency of WLEDs with triple-layer remote phosphor structures

The angular color uniformity (ACU) with the ability to evaluate chromatic performance of WLED has become an important target to achieve in producing higher-quality WLEDs. This paper studies the ACU enhancing effects of novel triple-phosphor configuration in lighting devices with remote phosphor structure. Moreover, the optical influences of remote phosphor structure with three phosphor layers (TL) on WLEDs properties are calculated and compared to the dual-layer (DL) one for reference. The experiments are applied to devices at 5 distinct correlated color temperature ranging from 5600-8500 K. The results presented that DL structure attains better color rendering index (CRI) than the TL one. Meanwhile, in terms of color quality scales (CQS), TL model shows higher values at all ACCTs, compared to the DL. Moreover, the luminous flux of DL configuration is lower than that of TL structure. In addition, the diversion of color temperature depicts as D-CCT in TL structure is much better than the value in DL structure, especially at high ACCT as 8500 K, which means TL is good for chromatic uniformity of high ACCTs WLEDs. These results proved that the triple-layer structure is superior and more effective to apply for acquiring the enhancement of WLEDs package.

Triple-layer remote phosphor structure: a novel option for the enhancement of WLEDs’ color quality and luminous flux

Abstract The remote phosphor as a lighting structure has outstanding luminous efficiency compared to other options, such as conformal or in-cup. However, the lack of uniformity in distributed color has prevented remote phosphor from wider development. The answer to the chromatic performance enhancement that has been suggested by numerous researchers is the multi-layer configuration with two or three different types of chromatic phosphor. The research purpose is to select the best configuration for multi-chip white LEDs (WLEDs) to achieve optimal results in color quality scale (CQS), color rendering index (CRI), light output and color homogeneity. WLEDs mentioned in this paper have two distinct color temperatures, 6600 K and 7700 K. Experimental results show that the remote phosphor structure with three phosphor layers is superior in terms of color rendering, chromatic performance, and emitted light. The deviation of correlated color measured in this structure is also low, which means that the color uniformity is greatly enhanced in this multi-layer lighting structure. This result can be demonstrated by analyzing the scattering characteristics of the phosphoric layers using the Mie theory. The research findings have proven the effectiveness of the multi-phosphor configuration and can serve as a guideline to fabricate WLEDs with better performance.

Enhancing color quality of WLEDs with dual-layer remote phosphor geometry

Abstract Usually, remote phosphor structures are beneficial in terms of flux but unfavorable in terms of color quality compared to conformal phosphor or in-cup phosphor packages. To eliminate this disadvantage, many studies have focused on increasing the chromatic quality of the remote phosphor configuration, which requires great efforts in improving two parameters of color: color rendering index (CRI) and color quality scale (CQS). CRI is known as the most useful quantitative method used to measure the ability of a light source to reproduce the colors of illuminated objects faithfully and naturally. Similarly, CQS is also a method of lighting quality determination and analysis, especially used as an alternative to the unsaturated CRI colors. In this paper, we proposed dual-layer remote phosphor structure as a novel method of CRI and CQS enhancement to improve WLEDs’ color quality. Five alike WLEDs but having different color temperatures in the range of 5600 K to 8500 K were applied in this study. The idea behind the study is to place a red phosphor layer SrwFxByOz:Eu2+,Sm2+ on the yellow phosphor layer YAG:Ce3+ and then determining an appropriate concentration of SrwFxByOz:Eu2+,Sm2+ added to achieve the highest color quality. The results point out that SrwFxByOz:Eu2+,Sm2+ brings great benefits to the improvement of CRI and CQS parameters. Specifically, the higher the SrwFxByOz:Eu2+,Sm2+ concentration results in the greater CRI and CQS, owning to the enriched red light components in the WLEDs. However, the flux has a tendency of dropping when SrwFxByOz:Eu2+,Sm2+ concentration rises excessively. This has been proved by using the Mie-scattering theory and the Lambert-Beer law. The results of this article are essential references for manufacturing WLEDs with higher chromatic quality.

First-principles study of resistive random access memory based on single-layer black phosphorous resistive layer

In this work, Ti3C2/single-layer black phosphorus (BP)/Ti3C2 resistive random access memory (RRAM) was studied based on the first-principles theory. First, after determining the size of the material, the Ti3C2/BP(100) interface was built. By studying the electrostatic potential of the interface, it was found that there was a Schottky barrier at the interface, and the barrier height was obtained by calculating the work function and the band structure of the interface. Next, a Ti3C2/BP(100)/Ti3C2 RRAM device was designed based on the mechanism of the Schottky barrier at the interface. The bipolar switching characteristics were confirmed after calculating the I–V curve of the device, in which the turn-on threshold voltage is about 1.5 V, the turn-off threshold voltage is about 0.5 V, and the switch ratio is greater than 105. However, there are still shortcomings such as insufficient drive current. So, in the end, the optimization program is determined through a series of studies of device doping and vacancy, and it is found that after a certain concentration of Mg atoms are adsorbed, the conductivity of the resistive switching layer can be increased, the interface barrier can be adjusted, and the device performance such as the turn-on voltage, drive current, and switching ratio can be improved. This work may have guiding significance and value for the experimental research of manufacturing a new two-dimensional material RRAM.

Study of red-emitting LaAsO4:Eu3+ phosphor for color rendering index improvement of WLEDs with dual-layer remote phosphor geometry

The remote phosphor structure is often disadvantageous in color quality but in terms of optics it is more convenient when compared to other phosphor structures such as conformal or in-cup ones. From this disadvantage, there are many studies to improve its chromatic output. In this research paper, we propose a dual-layer remote phosphor geometry for the improvement of white light-emitting diodes (WLEDs) in two parameters: color rendering index (CRI) and color quality scale (CQS). The 7700 K WLEDs are used in this study. The idea of the study is to place a red phosphor layer LaAsO4:Eu3+ on the yellow phosphor YAG: Ce3+, and then find the concentration of LaAsO4:Eu3+ in an appropriate way to achieve the highest color quality. The results showed that LaAsO4:Eu3+ bring great benefits for enhancing CRI and CQS. In particular, the greater the concentration of LaAsO4:Eu3+, the greater the CRI and CQS because the portion of red lights in WLEDs increases. However, the decrease in lumen output occurs when the concentration of LaAsO4:Eu3+ increases excessively. This is proved thanks to Mie-scattering theory and Beer-Lambert law. The results of important articles in WLEDs fabrication have greatly contributed to a higher white light quality.

RF performance evaluation of p-type NiO-pocket based β-Ga2O3/black phosphorous heterostructure MOSFET

The radio-frequency (RF) performance of the p-type NiO-pocket based β-Ga2O3/black phosphorous heterostructure MOSFET has been evaluated. The key figure of merits (FOMs) for device performance evaluation include the transconductance (g m) gate dependent intrinsic-capacitances (C gd and C gs), cutoff frequency (f T), gain bandwidth (GBW) product and output-conductance (g d). Similarly, power-gain (G p), power added efficiency (PAE), and output power (P OUT) are also investigated for large-signal continuous-wave (CW) RF performance evaluation. The motive behind the study is to improve the β-Ga2O3 MOS device performance along with a reduction in power losses and device associated leakages. To show the applicability of the designed device in RF applications, its RF FOMs are analyzed. With the outline characteristics of the ultrathin black phosphorous layer below the β-Ga2O3 channel region, the proposed device results in 1.09 times improvement in f T, with 0.7 times lower C gs, and 3.27 dB improved G P in comparison to the NiO-GO MOSFET. The results indicate that the designed NiO-GO/BP MOSFET has better RF performance with improved power gain and low leakages.

The application of green YF3:Er3+,Yb3+ and red MgSr3Si2O8:Eu2+,Mn2+ layers to remote phosphor LED

White light-emitting diodes (WLEDs) with quantum dots (QDs) and phosphor have pulled in huge consideration because of their incredible shading rendering capacity. In the bundling procedure, a QDs film and a phosphor silicone layer will in general be isolated for lessening the reabsorption misfortunes and keeping the QDs surface molecules in a good condition. This examination explored the bundling succession of QDs and phosphor layers to the optical and warm exhibitions of WLEDs. The emitted optical power and PL spectra were estimated and dissected, while an infrared warm imager was utilized to reenact and approve tentatively the temperature fields. The results reveal that at 60 mA, WLEDs with green QDs-on-phosphor type accomplished lumen output (LO) of 1578 lm, with shading rendering record (CRI) of Ra = 60, while the red QDs-on-phosphor type WLEDs exhibited lower LO of 1000 lm, with Ra = 82. In addition, the QDs-onphosphor type WLEDs generated less warmth than the other, and as a result, the most noteworthy temperature in this packaged type was lower than the other. Additionally, its temperature contrast can arrive at 12.3°C. Along these lines, regarding bundling arrangement, the QDs-on-phosphor type is an ideal bundling design to better the optical productivity and shading rendering capacity, as well as lower gadget temperature.