Cathodoluminescence Brightness Research Articles

Timescale of magma recharge for a crystal-rich mush: Perspectives from the compositional zoned quartz in Xiangshan caldera, SE China

Crystal-rich (>30 vol%) volcanic rocks, which are generally thought to be formed by the eruption of crystal-rich mush after its reactivation, have provided an important lens through which to view the connection of volcanic and plutonic rocks in the calderas worldwide. The crystal-rich rhyolitic porphyritic lava is widely exposed in Cretaceous calderas in the southeast China. However, the petrogenesis of crystal-rich porphyritic lava still remains controversial. Xiangshan caldera is a uranium mineralization related volcanic-plutonic complex, which is composed of first subcycle rhyodacite and second subcycle tuff, crystal-rich rhyolitic porphyritic lava, granite porphyry and quartz monzonitite porphyry. All the volcanic and plutonic rocks have consistent zircon U-Pb ages (135 to 133 Ma). Sr-Nd-Hf-O isotopic characteristics show that they all mainly originated from crust derived intermediate-silicic magma. Zircon εHf(t) values for inherited zircons from rhyolitic porphyritic lava and rhyodacite range from −6.9 to +9.5. Correspondingly, zircon Hf two-stage model ages of inherited zircons are 2.12 to 1.10 Ga, suggesting their derivation from the Neoproterozoic juvenile crust and the Archean to Paleoproterozoic ancient crust. The rhyolitic porphyritic lavas show higher SiO2 contents and Rb/Sr ratios, and more obvious negative anomalies of Eu/Eu*, Ba, Sr, P and Ti; The granite porphyry show lower SiO2 contents and Rb/Sr ratios, with weak negative anomalies of Eu/Eu*, Ba, Sr, P and Ti. Combined with similar Sr-Nd-Hf-O isotopic composition, they may be derived from the same magma reservoir. Lower εNd(t), εHf(t), δ18O values and older model ages of tuff indicate more contribution of older crustal material. The cathodoluminescence (CL) brightness is strongly correlated with Ti concentration in quartz. The CL of selected quartz grains from crystal-rich rhyolitic porphyritic lava and granite porphyry show brightness zoned mantles (Ti = 19 to 77 ppm) and bright rims (high-Ti; >70 ppm). Some grains have dark cores (low-Ti; <9 ppm). However, the Ti contents of the quartz in the tuff of the second subcycle are homogeneous. Resemble the crystal-rich rhyolitic porphyritic lavas, the rims of quartz phenocrysts in the granite porphyry have consistent CL-brightness with the quartz in groundmass and have small embayments caused by growth impediments in them, which is due to the pressure release. It indicates that the granite porphyry also migrated upward rather than in situ cumulate. The repeated rise of CL brightness and Ti contents in the mantle of quartz phenocrysts recorded the rise of temperature and/or the injection of more primitive magma, indicating several times of magma recharge in the magma reservoir. The timescale of Ti diffusion in the compositional zoned mantle of quartz documented an ephemeral reactivation and remobilization of the crystal-rich mush within several to 16 thousand years with at least 7 times of magma recharge which lasted for 17 years to >11 thousand years each time.

Diagnostic REE patterns of magmatic and hydrothermal apatite in the Zhuxi tungsten skarn deposit, China

Apatite is increasingly used as a tracer for petrogenetic and hydrothermal processes. We studied the cathodoluminescence (CL) texture and composition of igneous and hydrothermal apatite from the Zhuxi biotite granite and its associated hydrothermal tungsten system in the Late Mesozoic Jiangnan porphyry-skarn tungsten belt in South China. Both magmatic and hydrothermal apatite is anhedral to subhedral, with up to >1 mm grain size. Igneous apatite has relatively constant ΣREE + Y contents in the 2700–6500 ppm range (3970 ± 1003 ppm; n = 52). Hydrothermal apatite in exoskarn has lower ΣREE + Y contents in the range from <1 ppm to ∼1500 ppm, i.e. a strongly heterogeneous REE distribution (101 ± 253 ppm; n = 68). The ΣREE + Y contents correlate positively with CL brightness in both magmatic and hydrothermal apatite.The REE patterns of magmatic apatite display patterns similar to the host rock (Zhuxi biotite granite): generally flat ((La/Yb)N = 1.19–8.06), with moderately negative Eu anomalies (EuN/EuN* = 0.11–0.51), slightly positive Ce anomalies (CeN/CeN* = 1.05–1.12), and chondritic Y/Ho ratios (25–36, average = 30). The hydrothermal apatite is much different: downward-convex (MREE depleted) patterns ((La/Yb)N = 2.48–211), slightly to strongly positive Eu anomalies (EuN/EuN* = 1.11–540), slightly positive to moderately negative Ce anomalies (CeN/CeN* = 0.40–1.16), and non-chondritic Y/Ho ratios (40–152, average = 84). Since the hydrothermal samples are located outside of the pluton, excluding the influence of feldspar on Eu content, the differences of the Ce and Eu anomalies between magmatic and hydrothermal apatite from the retrograde skarn suggest that the retrograde skarn formed in a more oxidized environment than the granite.The low and variable contents of REEs, low Th/U, and non-chondritic Y/Ho ratios can be diagnostically used to distinguish hydrothermal from magmatic apatite, and the MREE-depleted REE pattern may be a common feature of apatite from retrograde tungsten skarn deposits.

Oldest syenitic intrusions of the Yilgarn Craton identified at Karari gold deposit, Carosue Dam camp, Western Australia?

Apatite was separated from four samples of syenite porphyry, taken from the Karari gold deposit, in the Kurnalpi Terrane of the Archean Kalgoorlie-Kurnalpi Rift, Eastern Goldfields Superterrane (EGST). The alkalic composition of the syenitic magmas inhibited zircon crystallisation, so apatite provided the best mineral for geochronological investigations. LA-ICP-MS analysis of U, Th and Pb isotopes in the apatite gave a relatively wide range of lower intercept ages, with large errors, ranging from 1 to 3%, using OD-306 apatite as the primary standard. Cathodoluminescent (CL)-darker cores that comprise the major volume of apatite grains are relatively homogeneous in two samples, with one having clear oscillatory zoning. These samples yielded intercept ages of 2701 ± 34 Ma and 2699 ± 25 Ma, respectively. These ages are interpreted to approximate the magmatic crystallisation age of the apatite. Younger intercept ages were generated by apatite from two other samples, which display more complex and heterogeneous patterns of CL brightness. The apatite ages from these two samples are interpreted to have been produced by integrated analysis of apatite that has been heterogeneously modified by younger events. However, the magnitude of the temporal gap between magma emplacement and closure of the U–Pb system in apatite from these two samples remains unknown. Our best estimate of the age of the magmatic apatite from at least two of the syenitic intrusions at Karari is ca 2.70 Ga, which identifies these as the oldest intrusions of the Syenitic Group of magmas yet identified in the EGST. However, if ages are corrected to offset observed in the 401 apatite secondary standard, the two oldest syenitic intrusions are dated at ca 2660 Ma.

Improvement of in-plane uniformity of cathodoluminescence from ZnO luminescent layers for electron beam excitation assisted optical microscope

We fabricated flat and homogeneous Al2O3/ZnO/Al2O3 heterostructure luminescent layers by atomic layer deposition (ALD) to serve as a nanometer-scaled light source for high-spatial-resolution optical microscopy based on electron beam excitation (EXA). A smooth surface was obtained by inserting an Al2O3 buffer layer and an Al2O3 barrier layer resulting in brighter and more uniform cathodoluminescence (CL) compared with that from a directly deposited ZnO layer. The root mean square (rms) value determined by atomic force microscope drastically decreased from 2.4 nm (for typical ZnO film) to 0.5 nm (for the six-layer pairs of the Al2O3/ZnO/Al2O3 heterostructure). The CL brightness increased by two times of that in the Al2O3/ZnO/Al2O3 heterostructure due to a waveguide effect. However, the increase in the number of the layer pairs from one to six reduced the CL brightness by half. The CL emission variability was about 30% improved that is supposed to enable high-resolution using Al2O3/ZnO/Al2O3 luminescent layers for an EXA microscope.

The cathodoluminescence degradation and surface characterization of β-Ca3(PO4)2:Tb phosphor

The cathodoluminescence (CL) degradation mechanism of β-Ca3(PO4)2:Tb phosphors induced under low voltage electron beam bombardment in a vacuum chamber maintained at an O2 pressure of 1×10−6Torr and a background pressure of 1×10−8Torr was investigated. The surface chemical composition of the degraded powders analyzed by X-ray photoelectron spectroscopy, suggested that a new compound of oxide based calcium layer (i.e. CaxOy; x<1, y>1) was formed on the surface. The initial removal of C from the surface and the formation of a CaxOy over layer on the phosphor surface during electron irradiation caused a noticeably change in the CL intensity. Especially, based on the Auger electron spectroscopy combined with CL spectroscopy data, it is observed that there was an obvious correlation between the metal oxide layer build-up and the small decrease in CL brightness of the phosphors. The CaxOy, however, stabilized the phosphor preventing further degradation in the CL intensity. The CL properties and possible mechanism by which the new metal oxides were formed on the surface due to a prolonged electron beam irradiation are discussed.

Lattice site dependent cathodoluminescence behavior and surface chemical changes in a Sr5(PO4)3F host

Eu activated Sr5(PO4)3F phosphor powders have been subjected to the electron bombardment at 2keV (10μA) at an oxygen pressure of 1×10−6Torr. The synthesized Sr5(PO4)3F phosphor was identical to the hexagonal apatite structure, with the Sr present at two different sites Cs (S1) and C3 (S2) in the Sr5(PO4)3F host, as inferred from the crystallographic study. Cathodoluminescence (CL) and Auger electron spectroscopy of the phosphor excited by the same electron beam were used to monitor changes in the surface state during prolonged electron bombardment. A direct correlation between the surface reactions and the degradation of the CL brightness was observed. Both C and F were depleted from the surface during electron bombardment. The postulated mechanism for the electron stimulated chemical reactions on the phosphor surface is electron beam dissociation of molecular species to atomic species, which subsequently react with C to form volatile compounds CO2, CH4, etc. and with Sr5(PO4)3F to form a non luminescence layer of metal oxides of Sr and P.

Quartz zoning and the pre-eruptive evolution of the ~340-ka Whakamaru magma systems, New Zealand

Cathodoluminescence (CL) zoning in quartz crystals from rhyolitic pumices in two ignimbrite members of the ~340-ka Whakamaru super-eruption deposits, Taupo Volcanic Zone, New Zealand, is investigated in conjunction with the analysis of Ti concentration in quartz to reconstruct the history of changing magma chamber conditions and to elucidate the eruption-triggering processes. CL intensity images are taken as a proxy for Ti concentration and thus temperature and/or pressure and/or compositional variations during crystal growth history. Estimates of the maximum temperature changes (i.e., assuming other factors influencing Ti uptake remain constant) are made using the TitaniQ geothermometer based on the Ti concentration in quartz. These results are reviewed in comparison with Fe–Ti oxide, feldspar-melt and amphibole geothermometry. Core-to-rim quartz Ti profiles record a marked change in conditions (temperature increase and/or pressure decrease and/or change in melt composition) causing and then following a significant resorption horizon in the outer parts of the crystals. Two alternative models that could explain the quartz Ti zonation invoke a temperature increase caused by mafic recharge and/or a pressure decrease due to magma ponding and re-equilibration at shallow crustal levels. Concomitant changes in melt composition and Ti activity may, however, also have strongly influenced Ti uptake into the quartz. Some crystals also show other marked increases in CL brightness internally, but any accompanying magmatic changes did not result in eruption. Diffusion modelling indicates that this significant change in conditions occurred over ~10–85 years prior to caldera-forming eruption. This rapid thermal pulse or pressure change is interpreted as evidence for open-system processes, and appears to record a magma chamber recharge event that rejuvenated the Whakamaru magma system (melt-dominant magma plus crystal mush), and potentially acted as a trigger for processes that led to eruption.

Moissanite (SiC) from kimberlites: Polytypes, trace elements, inclusions and speculations on origin

An extensive collection of moissanite (SiC) grains from the Mir, Aikhal and Udachnaya kimberlite pipes of Yakutia has been characterized in terms of structural perfection, defects and the major- and trace-element chemistry of SiC and its included phases. The natural grains are clearly distinct from synthetic SiC produced by various methods. Most of the natural SiC grains are 6H and 15R polytypes. Some of the grains (< 10%) show extremely complex Raman spectra indicating strongly disordered structures. Some grains also show zoning in impurities, C-isotope composition and cathodoluminescence brightness. Inclusions are heterogeneously distributed within the natural SiC; their size varies from a few nanometers to hundreds of microns. The most abundant inclusions in SiC are Si metal and iron silicide (FeSi 2); a Si–C–O phase with stoichiometry close to Si 4(C,O) 7 probably is related to the silicon oxycarbides. FeSi 2 commonly appears to have exsolved from Si metal; in some cases Ti metal then has exsolved from FeSi 2 to form symplectites. Trace elements are strongly concentrated in the inclusions of FeSi 2 and Si 4(C,O) 7. The trace-element patterns of these phases are generally similar in the different kimberlites, but there are some consistent minor differences between localities. The trace-element patterns of FeSi 2 and Si 4(C,O) 7 are strongly enriched in LREE/HREE and are broadly similar to the patterns of kimberlites, carbonatites and some diamond-forming fluids. However, extreme negative anomalies in Eu (and Sm) suggest highly reducing conditions. Yb also shows strong negative anomalies in FeSi 2 from all three localities, and in Si 4(C,O) 7 from Aikhal and Mir, but not in those from Udachnaya. Trace-element chemistry and the nature of the inclusions provide a reliable basis for distinguishing natural and synthetic SiC. Textural and chemical features and the presence of oxidation products (Si 4(C,O) 7 and SiO 2) suggest that moissanite grew at high temperatures and elevated pressures and was subsequently partly oxidised, also at high T. Several important features of moissanite grains from kimberlites are consistent with the formation of natural SiC by electrochemical processes in carbonate-silicate melts.

Millennial timescale resolution of rhyolite magma recharge at Tarawera volcano: insights from quartz chemistry and melt inclusions

Most rhyolite eruption episodes of Tarawera volcano have emitted several physiochemically distinct magma batches (∼1–10 km3). These episodes were separated on a millennial timescale. The magma batches were relatively homogeneous in temperature and composition at pumice scale (>4 cm), but experienced isolated crystallisation histories. At the sub-cm scale, matrix glasses have trace element compositions (Sr, Ba, Rb) that vary by factors up to 2.5, indicating incomplete mixing of separate melts. Some quartz-hosted melt inclusions are depleted in compatible trace elements (Sr, Ti, Ba) compared to enclosing matrix glasses. This could reflect re-melting of felsic crystals deeper in the crystal pile. Individual quartz crystals display a variety of cathodoluminescence brightness and Ti zoning patterns including rapid changes in melt chemistry and/or temperature (∼50–100°C), and point to multi-cycle crystallisation histories. The Tarawera magma system consisted of a crystal-rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion.

The Effect of Annealing Temperature on the CL Properties of Sol-Gel Derived Y2O3 : Re ( Re = Eu3 + , Tb3 + , Tm3 + ) Phosphors

Red, green, and blue-emitting Li-doped (, , or ) film phosphors were coated on sapphire substrates using a sol-gel technique in which yttrium nitrate, metal nitrate (, , or ), lithium carbonate, and citric acid were used as the precursor materials. The effect of annealing temperature on thin films and thick films on sapphire substrates was studied with respect to the structural and cathodoluminescence (CL) properties of the film phosphors. The structural and optical trends observed as a function of annealing temperature differed between the thin and thick films. The (, , or ) red, green, and blue thick films annealed at showed the highest volume and crystallinity of the phase and CL intensity of Li-doped red, green, and blue phosphors. These results for thick-film phosphors are discussed on the basis of the optical properties, such as the CL spectrum, color coordinates, brightness, and longevity.

Ultraviolet emitting (Y 1− xGd x) 2O 3− δ thin films deposited by radio frequency magnetron sputtering: Combinatorial modeling, synthesis, and rapid characterization

Gadolinium-doped, yttrium oxide thin films have been deposited on silicon (001) substrates by radio-frequency (RF) magnetron reactive sputtering that exhibit cathodoluminescence (CL) at ultraviolet frequencies. The maximum CL brightness occurred at λ∼314–315 nm characteristic of the 6P 3 / 2 → 8S ( λ = 314 nm) transition observed in Gd-doped, yttrium oxide powders. The radiative recombination takes place at the rare earth activator Gd 3+ site embedded in the Y 2O 3− δ host; the optical transition resides within the band gap of the Y 2O 3− δ host and the transition observed is characteristic of atomic gadolinium. A combinatorial approach to sputtering was used to deposit a film of variable composition from 1 to 23 at.% Gd in Y 2O 3− δ in order to rapidly discern the composition node of optimal CL brightness. A simulation was created for the purpose of predicting the film combinatorial composition for binary and ternary alloys prior to sputtering experiments in order to facilitate our combinatorial thin film synthesis technique. The model prediction varied from the real experimental composition profile by only 2.2 at.% Gd ± 1.6 at.% proving the predictor as a useful aide to complement combinatorial thin film experiments. A film of composition Y 1.56Gd 0.44O 3.25 (8.3 at.% Gd) yielded the maximum CL brightness. CL brightness increased continuously up to the 8.3 at.% Gd composition due to the increased number of activators present in the host. Beyond this composition the brightness drastically decreased. The oxygen composition in the combinatorial film was strongly dependent on the Gd composition; films were sub-stoichiometric δ > 0 below ∼6 at.% Gd and was over-stoichiometric δ < 0 beyond this composition.

Characterization and conductive coating of phosphors for improved brightness

In this study, the phosphors used in CRTs are coated with In 2O 3 conductive layer derived from the hydrolysis of indium chloride. The conductive coating retards/eliminates charging-up on the phosphor surface during the bombardment of the electrons and improves the cathodoluminescent brightness of the phosphor. However, the non-emissive conductive coating also degrades the cathodoluminescent brightness when it is too thick. The cathodoluminescent brightness increases initially with the amount of coating, reaches a maximum at 10 wt.% InCl 3, and decreases with further increase of coating. It is found that with a 10 wt.% InCl 3 coating, the brightness of phosphor increases by 20% at 500 V and 1 μA.

Enhancement of cathodoluminescence of ZnGa2O4:Mn thin-film phosphor by energetic particle bombardment

Enhancement of cathodoluminescence of manganese-activated zinc gallate (ZnGa2O4:Mn) thin-film phosphor by energetic particle bombardment is reported. The ZnGa2O4:Mn thin-film phosphor was grown at room temperature on silicon (100) substrates by rf magnetron sputter deposition from a 2 mol % Mn-doped ZnGa2O4 target in an oxygen–argon mixture. After the deposition, the films were annealed at 800 °C for 3 h in air. The influence of energetic particle bombardment on cathodoluminescent (CL) properties of ZnGa2O4:Mn films was investigated by varying a gas pressure during the sputter growth. Our results have shown that CL brightness from ZnGa2O4:Mn films grown at 2 mTorr was more than eight times higher than that of films grown at 20 mTorr. The remarkable improvement in CL brightness from ZnGa2O4:Mn films grown at a low pressure is presumably due to the energetic particle bombardment of the growing film surface yielding a densely packed microstructure and a better crystalline quality with a highly [110]-textured structure.

Critical issues in enhancing brightness in thin film phosphors for flat-panel display applications

Thin film phosphors have potential applications in field emission flat-panel displays. However, they are limited by the lower cathodoluminescent brightness in comparison to phosphor powders. In this paper, we have investigated the critical parameters that need to be optimized to increase the brightness of phosphor thin films. Specifically, we studied the role of surface roughness and optical properties of the substrate on the brightness of the phosphor films. Thin Y 2O 3:Eu phosphor films were deposited on various substrates (lanthanum aluminate, quartz, sapphire, and silicon) with thicknesses varying from 50 to 500 nm. A model that accounts for diffuse and specular or scattering effects has been developed to understand the effects of the microstructure on the emission characteristics of the cathodoluminescent films. The results from the model show that both the optical properties of the substrate and the surface roughness of the films play a critical role in controlling the brightness of laser deposited phosphor films.

The effect of ZnS content on the luminescence and electrical properties of ZnO : Zn phosphor

Zinc oxide phosphors (ZnO : Zn) were prepared by solid state sintering of ZnO powders with ZnS and screen printed onto ITO-coated glass substrate. The effect of ZnS content and sintering temperature on the cathodoluminescence brightness, efficiency and electrical properties of ZnO : Zn were studied. Samples with 5 wt % ZnS and sintered at 1100 °C exhibit the highest brightness and efficiency among all the compositions studied. The brightness of phosphors increases linearly as the accelerating voltage V and/or beam current I increases. While the efficiency decreases initially and then reaches a constant value as V and/or I increases. Both the conductivity σ and carrier concentration n of the phosphor increase with the increase of ZnS content in the starting composition. Results of Hall measurement suggest that the ZnO : Zn phosphor is an n-type conductor with an electron mobility of around 175 cm2/V-s. For specimen with 5 wt % ZnS, both σ and n increases initially with the increase of sintering temperature T, and reaches a constant value at T ≥ 1000 °C. The unreacted ZnS found in samples sintered at T < 1000 °C explains the temperature dependence of σ and n.

A Study on the Degradation of Cathodoluminescence of SrTiO3 : Pr , Al , Ga Phosphors Tailored for Low Voltage Display Applications

The mechanism of degradation on the low voltage cathodoluminescence (CL) efficiency of phosphors is investigated. The effect of carbon overlayer adsorbed on the phosphor surface from the vacuum ambient during the electron irradiation done in a high vacuum chamber causes a rapid degradation of low voltage CL noticeably. Especially, based on Auger electron spectroscopy combined with CL spectroscopy it is observed that there is obvious correlation between carbon buildup and loss of CL brightness of the phosphors characterized in this study. Also, it is shown that the increased amount of carbon adsorbed during the electron irradiation on the phosphor surface is completely removed by heating the degraded samples at 470°C for 30 min in air. Furthermore, the decreased CL intensity of degraded samples is recovered up to that of original ones together with the removal of carbon. From the present work, it is understood that the rapid degradation of low voltage CL of the phosphors is directly related to the formation of the carbon overlayer, but not related to a change in the emission properties of the luminescent center themselves. © 2001 The Electrochemical Society. All rights reserved.

REE, U, Th, and Hf distribution in zircon from Western Carpathian Variscan granitoids: A combined cathodoluminescence and ion microprobe study

A cathodoluminescence (CL) investigation on individual zircon crystals from Variscan S-type granites from the Western Carpathians has been combined with ion microprobe rare earth element (REE) and trace element analyses to explore possible connections between the CL emission of natural zircon crystals and their chemical composition. The work was supported by single zircon U-Pb dating, both by thermal ionization mass spectrometry (TIMS) and ion microprobe, which helped to identify inherited zircon cores derived from related protoliths and to constrain the ages of inheritance and anatexis. Neither the REE nor trace elements such as Y or Th were found to have any direct correlation with the CL brightness. The intensity of the CL signals was not directly reflected in the REE concentrations or the shape of the REE patterns. Uranium is probably the element responsible for quenching or suppressing the CL signals. Zircon cores inherited from different protoliths were distinguished by their REE patterns. This enabled, within a particular geological area, the identification of inherited cores which possibly originate from the same protolith and therefore might lie on the same discordance line, thereby improving the accuracy of inheritance ages inferred from TIMS single zircon analyses.

Electron beam induced degradation of a pulsed laser deposited ZnS:Cu,Au,Al thin film on a Si(1 0 0) substrate

ZnS:Cu,Au,Al thin film phosphors grown on Si(1 0 0) were subjected to an electron beam irradiation with beam energies ranging from 1 to 5 keV and current densities between 16 and 89 mA at O 2 and CO 2 partial pressure of 5×10 −7 Torr . Auger electron spectroscopy (AES) and the cathodoluminescence (CL), both excited by the same primary electron beam were utilised to monitor the changes in the surface composition and the luminous efficiency of the films during electron bombardment, respectively. The degradation mechanism for these reactive gases in ambient was manifested by the depletion of S and the formation of a non-luminescent ZnO layer on the surface of the phosphor. The degradation was more severe under O 2 ambient compared to the same partial pressure of CO 2 during electron beam bombardment, which is attributed to the free energy of formation of ZnO from ZnS when these respective gases are used. The degradation rate also depends on the energy of the electron beam, decreasing with increasing beam energy. This was interpreted according to the ionisation energy cross-section profile. The CL brightness increased exponentially with the increasing beam energy as more free carriers that will subsequently recombine yielding CL, are excited at higher beam energies.

Structure and Luminescence Properties of the ZnS:Cu, Al Phosphor for Low Voltage Excitation

The ZnS:Cu, Al phosphor has been studied for low voltage excitation field emission devices. To improve the cathodoluminescence (CL) brightness, the phosphor has been synthesized with iodide-type alkaline and alkali-earth metal as fluxes. CuI and were used as an activator and coactivator, respectively. The phosphor has been characterized in comparison with commercially available cathode ray tubes (CRTs) phosphor and conventionally prepared ones. Newly synthesized ZnS:Cu, Al phosphor prepared with iodide-type fluxes has shown higher CL brightness than commercially available phosphor and conventionally prepared ones. The phosphor structure has been analyzed using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. From the analysis, the phosphor particles were composed of cubic and hexagonal phases. The cubic phase was much more formed when iodide-type fluxes were used. This cubic phase helps the phosphor to have high brightness at low voltage operations. © 2001 The Electrochemical Society. All rights reserved.

Effect of temperature on the degradation of ZnS FED phosphors

AbstractThe changes in cathodoluminescent brightness and changes in the surface chemistry of ZnS:Cu,Al,Au have been investigated using Auger electron spectroscopy (AES) and a photospectrometer. The ZnS:Cu,Al,Au phosphor powders have been subjected to electron beam bombardment of 2 keV, with an electron beam current density of 88 mA cm−2 at an oxygen pressure of 2 × 10−6 Torr. The studies were carried out between room temperature and 310 °C. Degradation was manifested by a non‐luminescent ZnO layer that formed on the surface of the phosphor according to the electron‐stimulated surface chemical reaction (ESSCR) mechanism. An increase in temperature led to a decrease in the surface reaction rate due to a decrease in the mean surface lifetime of the oxygen molecules on the surface, with a direct decrease in the ESSCR probability. Without the presence of the electron beam, no chemical reactions occurred on the surface up to 310 °C. Local heating due to the electron beam irradiation is not responsible for the chemical reactions on the ZnS phosphor surface. Copyright © 2001 John Wiley &amp; Sons, Ltd.