Transparent Glass Research Articles

Structural and luminescence properties of transparent borate glass co-doped with Gd3+/Pr3+ for photonics application

A new glass system of lithium borate doped with Gd2O3 and Pr2O3 has been fabricated using a conventional melt quenching technique. The physical parameters, such as density, molar volume, and refractive index, were measured and found to increase as the concentrations of lanthanide oxide (Gd2O3 and Pr2O3) in the glass increased, revealing the underlying structural changes. According to the results of XRD and FTIR, the synthesized glasses exhibited an amorphous structure, and borate complexes served as the triangular BO3, tetrahedral BO4, and OH group amounts in oxide glass. The photoluminescence (PL) spectra show characteristic emission bands resulting from f-f transitions of Pr3+ ions. The strongest emission occurred at 603 nm, corresponding to the transition from the 1D2 state to the 3H4 state. The optimal concentration of Gd2O3 for maximizing emission intensity was found to be 5.0 mol%, and this concentration will be used in the next experiment with varying Pr2O3 concentrations. In the subsequent experiment, emission spectra were recorded by exciting the glass with light at wavelengths of 445 nm, 469 nm, and 483 nm. The resulting emission spectra displayed the characteristic pattern associated with the emission of Pr3+. This emission peak at 603 nm represented the strongest intensity in the spectra, which is a common characteristic of Pr3+ emission. The emission intensity of the glasses initially increases with increasing concentrations of Pr2O3 up to 0.3 mol%, but beyond this concentration, the emission intensity starts to decrease. This behavior indicates the occurrence of a quenching effect at the 0.3 mol% concentration of Pr2O3. X-ray absorption near-edge structure (XANES) analysis confirmed that praseodymium ions were predominantly in the 3 + oxidation state. The chemical composition of the created glass was confirmed to be suitable for photonics applications.

Additive Manufacturing of Large-scale Metal Mesh with Core-shell Composite Structure for Transparent Electromagnetic Shielding/glass Heater

Transparent electromagnetic (EM) shielding glass with a metal mesh has significant potential for application in different fields of EM radiation and anti-EM interference light-transmitting observation windows. In particular, a transparent EM-shielding glass with a large-aspect-ratio metal mesh can effectively alleviate the contradictory problems of shielding effectiveness and light-transmission performance constraints. However, the fabrication of high-aspect-ratio metal meshes on glass substrates has problems such as high cost, complex processes, low efficiency, small area, and easy damage issues, which limit their application in the field of high-performance, transparent EM-shielding glass. Therefore, this paper proposes a composite additive manufacturing process based on electric-field-driven microjet 3D printing and electroplating. By fabricating metal meshes with an Ag-Cu core-shell structure on a glass substrate, EM-shielding glass with high shielding efficiency and light transmission can be manufactured without increasing the aspect ratio of the metal meshes. The prepared Ag-Cu composite metal mesh has excellent optoelectronic properties (period 250 μm, line width 10 μm, 90.1% transmission at 550 nm visible light, square resistance 0.21 Ω/sq), efficient electrothermal effect (3 V DC voltage can reach 189 °C steady-state temperature), stable EM-shielding effectiveness (average shielding effectiveness 23 dB at X-band), and acceptable mechanical and environmental stability (less than 3% change in square resistance after 150-times adhesion test and less than 6% and 0.6% change in resistance after 72 h in acid and alkali environments, respectively). This method provides a new solution for the mass production of high-performance large-area transparent electric heating/EM-shielding glass.

Effect of thermocompression on properties of transparent glass-ceramics containing quantum dots

A novel strategy for preparing transparent glass-ceramics with a uniform quantum-dot size and high transparency via thermocompression is reported. Borophosphate glass containing the Cs–Pb–Br component is prepared using the conventional melting method. The glass is then pressed with a piece of stainless steel to generate thermocompression during the crystallization heat treatment, by which small and uniform-sized nanocrystals of CsPbBr3 quantum dots are produced in glass. Thermocompression reduces the specific surface energy of the nanocrystals and inhibits the abnormal growth of microcrystals, thereby reducing the average particle size from 7 to 4 nm and completing the growth of microcrystals. This significantly increases the transmittance of the glass-ceramics and enhances the luminescence intensity by approximately threefold. The experimental results show that low-intensity pressure can control the structure and properties of glass-ceramics during the growth of microcrystals in glass, which is a new process for preparing transparent microcrystalline glass.

STRUCTURAL DESIGN OF Eu<sup>2+</sup>-CONTAINING GLASS AND GLASS-CERAMICS BASED ON THE SYSTEM BaO–ZrO<sub>2</sub>–SiO<sub>2</sub>–MgF<sub>2</sub> FOR LED APPLICATION

For the first time, an approach to designing the structure of Eu2+ containing silicate glass-ceramics materials has been experimentally implemented, which consists in the fact that rare earth activator is introduced into various crystals formed during glass crystallization. Transparent Eu-containing glass and glass ceramics based on the system BaO–ZrO2–SiO2–MgF2 were prepared by the traditional glass melting method at 1450°C. The crystal structure and properties of materials were characterized by XRD analysis and photoluminescence spectroscopy during different stages of glass crystallization. It is shown that the simultaneous incorporation of Eu into different silicate crystals (Ba2SiO4, BaMgSiO4, and BaSiO3) formed during the glass crystallization leads to the formation of a material with a wide luminescence band in the visible part of the spectrum. The study of photoluminescence and luminescence excitation spectra of the glass suggests the possibility of energy transfer from Eu2+ to Eu3+ ions. The structures of Eu2+ luminescent centers are similar in the glass and glass-ceramics that is related to some phase separation in the glass before crystallization. The study of luminescence properties of prepared materials showed that these materials can be promising for the application in LEDs techniques.

Composite material with enhanced recyclability as encapsulant for photovoltaic modules

Encapsulation of photovoltaic cells was carried out using a transparent glass fiber reinforced composite with enhanced chemical recyclability based on a matrix of an epoxy resin containing cleavable functional groups. The current-voltage curves showed a decrease of 6.3% on the short-circuit current (Isc) after encapsulation of the cell, lower than the one observed for the reference non-recyclable standard epoxy composite. Its performance stability under thermal cycling, ultraviolet (UV), and damp-heat exposure was evaluated and compared with the one of the reference standard epoxy. Both resins showed good stability performance under UV exposure and thermal cycling accelerated aging. Moreover, a power loss below the 5% allowed by the photovoltaic standard was observed for the recyclable resin after 1000 h of damp-heat exposure, even the pronounced loss of 4.7% in power remains a concern. Regarding the recyclability, the composite was dissolved in acetic acid dissolution and glass fiber fabrics were successfully recovered. A new module was manufactured with these fabrics, showing this time a loss of 12% in Isc comparing with the non-encapsulated cell. Further work will consider improving the moisture barrier properties of the composite, and adjusting the recycling conditions to allow component recovery valid for new modules.

Reversible Intercalation of Protons in Tungsten Oxide Films for Multi-Transduction Sensor Applications

Tungsten oxide films under electrochemical bias, can form tungsten oxide bronzes (MxWO3 with M being small cations such as H+ or Li+) featuring high electronic conductivity and change in coloration to deep blue1. This doping process occurs through the reduction of W6+, as described by the following equation:WO3 + x H+ + xe- -> HxWO3The bronze phase can also be formed through exposure of tungsten oxide to H2 at high temperatures (> 200 oC) or in presence of catalysts2, as described by the following equation:WO3 + x/2 H2 -> HxWO3 Because of the significant changes in both optical and electrical proprieties of the films, electrochemical control of proton doping can be used as a strategy for the development of ion-gated transistors3,4, hydrogen sensors and smart windows5.In this work, we report the use of thin films prepared by sol-gel synthesis using polyperoxotungstic acid (PPTA) as a precursor. We used three different types of substrates (conductive transparent fluorine-doped tin oxide (FTO) glass, Si/SiO2 patterned with Au source-drain electrodes and Interdigitated electrodes patterned on transparent glass) to study the changes of color and conductivity following the formation of the bronze in both electrochemical and dry environments. In electrochemical environment, we show that gating by ionic liquid in transistor configuration can be used to propose an iontronic sensor to detect H2 and H2O6. In dry environment, we show that simultaneous monitoring of visible light transmittance and electrical conductivity can be used a double transducer for H2 sensors6.1 M. S. Whittingham, in Solid State Ionics, 2004, vol. 168, pp. 255–263.2 C. C. Chan, W. C. Hsu, C. C. Chang and C. S. Hsu, Sensors and Actuators, B: Chemical, 2011, 157, 504–509.3 M. Barbosa, X. Meng, F. Soavi, C. Santato and M. O. Orlandi, J Mater Chem C Mater, 2018, 6, 1980–1987.4 G. V. de Oliveira Silva, A. Subramanian, X. Meng, S. Zhang, M. S. Barbosa, B. Baloukas, D. Chartrand, J. C. Gonzáles, M. O. Orlandi, F. Soavi, F. Cicoira and C. Santato, J Phys D Appl Phys,5 G. Cai, J. Wang and P. S. Lee, Acc Chem Res, 2016, 49, 1469–1476.6 M. S. Barbosa, R. A. da Silva, C. Santato and M. O. Orlandi, Journal of Vacuum Science & Technology A, 2022, 40, 013202.

Synthesis and evaluation of Li2O-2B2O3 glass chips for gamma radiation dosimetry applications

We report the fabrication of 10 mm × 10 mm × 1 mm, Li2O-2B2O3 glass chips using melt quench method. Melt produced due to solid state reaction between Li2CO3 and H3BO3 at 950°C, quenched at stainless steel die and annealed at 350°C resulted in production of highly transparent glass chips. Glass chips irradiated to various gamma radiations and thermo-luminescence measurement performed using linear temperature profile with heating rate 2°C/s. A broad glow curve is obtained with peak at 185°C. Further linearity of TL response with gamma dose studied in gamma dose range 100 mGy to 50 Gy. TL intensity and integrated counts are found linearly with gamma dose. The TL sensitivity of glass chips were found to be ∼52 counts/mGy. Repeatability of TL Dosimetric performance is found to be within ±10% and dose rate dependence is also found within ±10% in 50 mGy/hr to 3000 mGy/hr dose rate range. The prepared glass chips can be utilized as thermo-luminescent dosimeter for gamma dose 100 mGy and higher.

A critical review of infrared transparent oxide glasses

There is a growing demand for high-performance infrared (IR) materials with longer wavelength optical transmission, higher mechanical strength, and increased thermal stability. Although crystalline materials, namely transparent ceramics, have shown suitable optical properties, they are difficult and expensive to produce, making glasses more attractive for many applications. Several reviews have been published discussing chalcogenide and halide glasses, but none cover relevant oxide glass families in an overarching review. This article provides a discussion of relevant oxide glass systems involved in IR transmission as well as their primary applications. Glass compositional systems reviewed include silicates, tellurites, germanates, and vanadates. Emphasis on structure-property relationships, processing methods, and transparency limits for each composition is included. The applications of these materials include optical communications, thermal imaging, optical switching, and optical modulation. Finally, current material challenges are discussed with perspectives and outlooks on the future of IR transparent oxide glasses.

SERS Sensing of Dopamine with Fe(III)-Sensitized Nanogaps in Recleanable AuNP Monolayer Films.

Sensing of neurotransmitters (NTs) down to nm concentrations is demonstrated by utilizing self-assembled monolayers of plasmonic 60nm Au nanoparticles in close-packed arrays immobilized onto glass substrates. Multiplicative surface-enhanced Raman spectroscopy enhancements are achieved by integrating Fe(III) sensitizers into the precisely-defined <1nm nanogaps, to target dopamine (DA) sensing. The transparent glass substrates allow for efficient access from both sides of the monolayer aggregate films by fluid and light, allowing repeated sensing in different analytes. Repeated reusability after analyte sensing is shown through oxygen plasma cleaning protocols, which restore pristine conditions for the nanogaps. Examining binding competition in multiplexed sensing of two catecholamine NTs, DA and epinephrine, reveals their bidentate binding and their interactions. These systems are promising for widespread microfluidic integration enabling a wide range of continuous biofluid monitoring for applications in precision health.

Polyvinylidene Fluoride (PVDF) Crystallization Kinetics in an Electric Field

To study the effect of applied electric field on polymer crystallization, the crystallization of polyvinylidene fluoride (PVDF) was observed under modified polarized optical microscopy. The PVDF melts were crystallized based on programmed temperature, changes between two transparent conductive glass electrodes, on which a DC electric field was applied. The observations revealed that without the electric field, crystallizations below 160 °C resulted in only α-form crystals, while, at elevated temperatures, the formation of γ-form crystals also occurred. By applying the electric field at 1.7 kV/cm, γ-form crystals started emerging at the slightly lower temperature of 158 °C. Further examinations showed that both crystals, α-form and γ-form, grew at a greater rate with increasing field strength. A careful calculation of the Avrami parameters supported the data that the electric field enhanced the crystallization kinetics. Careful calculation based on the Laurientz–Hoffmann approach revealed that applying the electric field decreased the required energy for PVDF crystallization. The folding surface free energy of the PVDF crystallization, 1.76 × 10−2 Jm−2, was reduced to 1.57 × 10−2 Jm−2 and 1.43 × 10−2 Jm−2 after applying electric fields of 0.8 and 1.7 kVcm−1, respectively. We suggest that the electric field promoted the polymer chain alignment during the crystallization; as a result, it accelerated the polymer crystallization and lowered the energy requirement for crystallization.

Local and high‐strength joining of transparent glass and glass‐ceramics by femtosecond Bessel beam

AbstractThe creation of robust joint among different materials with notably different coefficients of thermal expansion (CTE) is an urgent task for the development of the engineering, laser technology, and aerospace industry. In this regard, femtosecond laser welding is a promising technique for efficient adhesion‐free bonding of transparent materials. This paper reports on the laser welding of laser phosphate glass (CTE = 110 × 10−7 K−1) and spinel‐based glass–ceramic (CTE = 50 × 10−7 K−1) by the Bessel beam. Dependencies of weld geometric parameters on the pulse energy and scanning speed were investigated, and the laser exposure conditions were optimized for durable welding. The weld joints were tested on shear strength, which was shown to be as record high as up to 147 MPa. Atomic force microscopy, Raman spectroscopy, and elemental analysis were used to investigate the structure and morphology of the weld after its fracture, which revealed the laser‐induced amorphization of glass–ceramics and the formation of strong interconnection by laser‐driven mutual diffusion of two glassy phases. The results demonstrate the prospects for using femtosecond lasers for efficient industrial welding of a wide range of materials.

One-step assembly of organic-inorganic hybrid coatings with superior thermal insulation, sustainable antifogging and self-cleaning capabilities

Multifunctional transparent glass integrating energy-saving and antifogging properties has receiving continuous attention in basic research and practical applications, which is still plagued by the lack of simple and general methods for low-cost and large-area fabrication. Herein, a multifunctional window with high thermal insulation, antifogging, and self-cleaning functions is rationally fabricated via coating a mixture of polyacrylic acid (PAA), polypropylene glycol (PPG), 3-glycidyloxypropyltrimethoxysilane (KH-560), and cesium tungsten bronze (CWO) nanoparticles on a monolayer film. The synergistic effect between the plentiful hydroxyl/carboxyl groups of PAA/PPG and the nano-textured surface induced by CWO nanoparticles enabled the monolayer film to exhibit superhydrophilic, self-cleaning and antifogging capabilities. The film maintains its antifogging properties even after 80 rubbings of dust-free cloth and 120 days of exposure tests at room temperature. Moreover, the as-prepared window can reduce the indoor temperature by 15.8 °C compared to a normal window at noon. The energy simulation results demonstrate that such windows can reduce energy consumption by 18.9 % in local cities compared to traditional windows. The high visible light transmittance, low haze, stable and durable antifogging ability, distinguished energy-saving effect and climate adaptability, as well as the solution-based process of this multifunctional window make it promising for architectural and automotive glass applications.

An optically transparent dual-band frequency selective surface for polarization independent RF shielding

This article reports on a compact dual band, Frequency Selective Surface (FSS) based spatial filter for Wi-Fi and WLAN shielding applications on a transparent glass surface with optical transparency of 70%. The unit cell comprises an outer square loop resonator with a disconnected and concentric annular ring resonator. To introduce frequency tuning and compactness T shape stubs are strategically loaded on these resonators and it is ensured that the mutual coupling remains minimal. The outer square resonator suppresses the 2.4 GHz band, and the inner circular ring resonator stops the 5.4 GHz band. The unit element is four-fold symmetric thus it offers complete polarization independence. A detailed parametric and electromagnetic field analysis has been conducted to elucidate the significance of different sections of the unit element. An equivalent lumped circuit model is also derived for the proposed unit element to better explain the underlying working mechanism. A finite prototype of 15 × 11 elements is fabricated on a soda lime float glass by using ordinary adhesive copper foils with a standard chemical etching process. Polarization independence and angular stability up to 45° are measured and compared with the simulated responses. The FSS shield offers frequency suppression up to 45 dB and 43 dB for 2.4 GHz and 5.4 GHz bands respectively. With high optical transparency, the design allows maximum light through it and causes no extra burden on energy consumption for indoor applications. The compact dual band design and the possibility of direct application on host surfaces like glass windows and doors make this design an excellent candidate for data security and privacy applications in secure installations with an esthetically pleasing outlook.

Diety Nike-Victoria of the late Antique period on the territory of Georgia

The states on the territory of Georgia were part of the Classical antiquity ecumene. Accordingly, both Iberia and Colchis had close trade-economic and cultural relations with the Roman Empire, from where the deities popular in the empire spread to the territory of Georgia. Among them, a special place is occupied by the ancient god of victory, Nike (Ancient Greek: Νίκη). The name Nike is believed to date back to the pre- Greek period. In Greek mythology, Nike appears as a companion of Zeus and Athena. In Greek art, the deity is mainly depicted with symbols of victory – wings, a crown and a palm branch, but we also find a wingless Nike. In Roman reality, the Victoria (Latin: Victoria) corresponded to Nike. Research has shown that the deity Nike (Victoria) was one of the most widespread cults in late ancient Iberia, which is the result of political and cultural relations with the Greco-Roman world. In late antiquity, the cult of Nike (Victoria) was recorded on the territory of Georgia in the Kingdom of Kartli (Iberia) – on the territory of Greater Mtskheta, Urbnisi, Zhinvali... Since the Hellenistic period, religious syncretism was also reflected on the engraved gems found on the territory of Kartli. Athena-Tikhe-Fortuna- Demeter-Nike depicted in an oval-shaped cornelian intaglio in a fragment of an iron ring. Tomb №27 of Karniskhevi, 2nd-3rd centuries. Nike-Fortuna-Athena is depicted in an oval-shaped white, transparent glass intaglio in an iron seal. Urbnisi necropolis. Tomb №205. 1st-early 2nd century AD. Seals with the image of the deity Nike (Victoria) found in the territory of Georgia belonged to all layers of society. Gemas can be found both individually and in gold, silver and bronze rings. Intaglios with the image of the deity are made of: carnelian, glas, almadine, which are inserted into iron, bronze, silver and gold rings. It is noteworthy that the cult of Nike (Victoria) is mainly prevalent in urban centers. From the above, we can conclude that Nike (Victoria) was popular and in our opinion, mainly among the Romanized population.

High damage-resistance and fracture toughness of transparent Nb-doped barium aluminoborate glass ceramics

Glass-ceramics offer the opportunity to address the main disadvantage of oxide glasses, namely low fracture toughness. The presence of crystals can improve the fracture toughness (crack growth resistance), but the crack initiation resistance will typically be deteriorated due to the induced residual stresses. Excessive crystal content and large crystal size can also lead to a loss of transparency. In this work, we report a Nb-doped barium aluminoborate glass-ceramic, for which both the crack initiation resistance (CR) and fracture toughness (KIc) get improved upon heat treatment, while still maintaining some transparency. Relying on combined structural and mechanical characterizations, we demonstrate that the coordination numbers of B and Al in the glass phase decrease upon heat treatment, which is beneficial to energy dissipation under mechanical stress to improve CR. Furthermore, the formed piezoelectric crystal phase BaNb2O6 also helps to improve both CR and KIc, likely by converting the stress-induced mechanical energy into electric energy. Meanwhile, the increase in crystallinity and crystal size after heat treatment also leads to higher KIc of the glass-ceramics. These findings thus help address the difficult problem of simultaneously improving the resistances to crack initiation and growth, which will facilitate the future design of transparent, yet highly damage-resistant and damage-tolerant glass ceramics.

An allusive realization on the performance analysis of glass to glass, glass to tedlar and aluminum base flexible photovoltaic (PV) module

The photovoltaic effect plays a significant role in power generation by using solar PV modules. The two most popular types of PV panels majorly available in the market: Glass-to-Tedlar (G-T) and Glass-to-Glass (G-G) type. Both G-T and G-G type of modules are rigid in structure due to the involvement of transparent glass cover on the top of the module. In order to have non rig-id or flexible type of module, a module structure with aluminum as base and transparent plastic sheet at the top has been taken which is known as flexible type of PV module (F-Al). The use of plastic and aluminum makes these modules more flexible and lighter in weight as compared with G-T and G-G type of PV modules. The advantage of using F-Al PV module is that it can easily be modified into desired shapes. Initially, the mathematical modeling of F-Al PV module has been developed on Simulink. The different set of data for these three types of modules has been taken for analyzing the performance of these modules. The performance analysis of G-T type, G-G type and F-Al type of PV modules have been compared in terms of efficiency, cell temperature, daily energy production. The maximum electrical efficiency has been observed with G-G PV module. It is also observed that being with flexible nature, efficiencies of F-Al PV modules are almost comparable with G-T modules. The cell temperature of F-Al PV module and G-T PV module is found to be larger than G-G module. The daily electrical energy produc-tion was found to be more with G-G module in comparison to G-T and F-Al PV modules for a typical day in the month of April, 2019. It is also observed that due to flexible nature of F-Al module, efficiency is also converging faster towards regression line in comparison to G-G and G-T module. Further, efficiency and daily energy consumption of all three modules of PV panel are realized through artificial neural network (ANN). It is observed that least mean square error (MSE) is obtained with F-Al in comparison to G-G and G-T under the implication of ANN. Therefore, additional feature of least MSE for F-Al makes its preferable over others.

Photonic Characterization and Modeling of Highly Efficient Color Conversion Layers With External Reflectors

We propose a new method for fabricating arrays of colloidal quantum dots for color conversion layers (CCLs) with atomic layer deposited (ALD) encapsulation. Semiconductor processes were used to transfer the CCL onto a transparent glass substrate. This method enables pixels as small as 5 μm, and the pixel's size and pitch can be controlled through the semiconductor process and mask layout. A dual-color array with a red-and-green CCL was also demonstrated to be suitable for microdisplay applications in experiments. The best color conversion efficiency of a single color CCL reached as high as 20.7%. A set of distributed Bragg reflector mirrors was used to increase photon recycling, and these mirrors yielded an increase in peak intensity of 35.7%. We formulated a model of incoherent reflection and transmission to calculate the changes in CCL properties when mirrors are added; this model had close fit with results from experiments in which mirrors of different reflection coefficients were used. Through the use of ALD, the CCL can be stored at a normal room-temperature environment for more than 9000 hours, and the projected lifetime is linearly extrapolated to be 44,041 hours.

Fabrication of patterned transparent conductive glass via laser metal transfer for efficient electrical heating and antibacteria

Fabrication of patterned transparent conductive glass via laser metal transfer for efficient electrical heating and antibacteria

New measurement method of displacement susceptibility based on time‐domain current and potential combined spectra

AbstractDisplacement susceptibility is a very important parameter to characterise the displacement polarisation of dielectrics. Two methods based on the time‐domain current and potential combined spectra are proposed to measure the displacement susceptibility. One is based on the time‐domain polarisation current and decay potential combined spectra, and the other is based on the time‐domain depolarisation current and recovery potential combined spectra. The principle of the proposed methods are verified by simulation. In addition, a measurement system for the two proposed methods is built and is used to measure the displacement susceptibility of transparent organic glass and opaque nonlinear field grading materials. The experimental results are compared with those of the present optical method and the frequency‐domain method. Simulation and experimental results show that the proposed methods for the measurement of displacement susceptibility are feasible and practical, which lays a foundation for the research on the polarisation characterisation of dielectrics.

Self-luminescence of BaF2-B2O3 glass prepared by reduction

This study discovered that a transparent BaF2-B2O3 glass system without rare-earth ions prepared under CO-reducing atmosphere exhibited orange-red self-luminescence under near-UV light, generating broadband luminescence from 550∼850 nm centered at 650 nm under broadband light excitation at about 397 nm. Based on the results of spectra, electron spin resonance, Raman, and X-ray photoelectron spectroscopy, it is proposed that the luminescence phenomenon is due to the s→p transition of B2+ generated inside the glass under the reducing atmosphere. This new luminescent glass has the potential to be an orange-red luminescent material excited by a light-emitting diode.