Copper-Activated Zinc Sulfide Phosphors with Trivalent Substituents

CuGaS~ and ZnS form solid solutions over the entire range with some evidence for compound formation at 33 1/3 mole % CuGaS~. Emission under 3650.~ excitation shifts from green to red with increase in CuGaS~ concentration. Samples with more than 20 % CuGaS2 do not luminesce at room temperature but, at --195~ fairly bright emission is observed with up to 95% CuGaS2. AgGaS~ is soluble in ZnS to about 5-10 mole %, above which separation of AgeS is observed. Emission under 3650A excitation shifts from the blue (0.01% AgGaS2) to yellow (10% AgGaS~).The ternary sulfides, CuGaS~ and AgGaS~, have the chalcopyrite structure which is closely related to the zinc blende structure of cubic ZnS (1). In these compounds, two different atomic species occupy equivalent lattice sites on the zinc blende lattice. In CuGaS~, a z 5.34A and c = 10.47A. (c/a = 1.96) while in AgGaS2, a = 5.74A and c = 10.26A (c/a = 1.79) (2).Because of the similarities in structure, unit cell dimensions, and bond type, the ternary sulfides may form solid solutions with ZnS. In such solid solutions, the ternary compounds would not only change the unit cell dimension of ZnS, but may also affect the observed luminescence in ZnS: Cu,Ga and ZnS:Ag,Ga phosphors. Cu and Ag are activators and Ga is a coactivator in normal ZnS phosphors with green and blue emission.The solubility of these activators in ZnS is dependent on the presence of charge-compensating ions which usually function as coactivators (3). For instance, in ZnS: Cu with no chemical coactivator added, Froelich reported that only about 4x 104 g-atoms Cu/mole ZnS is retained in the lattice after firing (4). In contrast, at least 9x 10 -~ g-atom Cu/mole ZnS is retained in the ZnS:Cu,A1 phosphor with orange emission (5). Incorporation of the larger concentration of Cu in the latter case is possible because of the simultaneous incorporation of A1 as AI~S~. In this phosphor, the A1 was added to ZnS as an oxy-salt and converted to AI~S~ during the firing process in H2S at 1100~176It is questionable whether a large amount of AI~O~ would be converted completely to ALS~ when fired in the presence of ZnS in an H~S stream. Equimolar mixtures of ZnS and AI~O~, for instance, when so fired do not yield ZnALS,, the compound expected on complete conversion of the oxide to the sulfide. In all probability, addition of A1 as the oxide or oxysalt limits the solubility of Cu because of incomplete conversion to AI~S~. However, if the activator and coactivator are added as the ternary sulfide, the oxide conversion is circumvented. Further, activator and coactivator are added in exactly stoichiometric amounts in a form which facilitates incorporation in the lattice.It is the purpose of this paper to report results of studies in the systems CuGaS~-ZnS and AgGaS2-ZnS. Of special interest will be the structural data, limits of solubility, and luminescent properties. In these systems the concentrations of Cu or Ag in ZnS far exceed those reported in the literature, and with the increased concentrations of activators incorporated ...

Section: Discussionmentioning

confidence: 95%

Investigations in the CuGaS[sub 2]-ZnS and AgGaS[sub 2] -ZnS Systems

Apple

1958

“…Klasens (2) attributed these long wave-length bands to the radiative recombination of a free hole with an electron trapped at the coactivator. Froelich (3) reported long wave-length emission for Cu and self-activated ZnS phosphors which were coactivated with quite high concentrations of A1. Emission peaks are at 5880 and 5000A, respectively.…”

mentioning

confidence: 99%

Associated Donor-Acceptor Luminescent Centers in Zinc Sulfide Phosphors

Apple

Williams

1959

104

Zinc sulfide activated with copper or silver and coactivated with gallium or indium shows two emission bands. The shorter wave-length band does not involve the ground state of the coactivator or donor, whereas the longer wavelength band does. Both bands involve the ground state of the activator or acceptor. The factors contributing to the emission intensities from the various associated donor-acceptor pairs are discussed theoretically. The dependences on temperature and on concentrations of activator and coactivator are in accord with the longer wave-length band involving a highly associated donoracceptor pair. In addition, the energy levels of the donors, as obtained from thermoluminescent data, are correlated on the basis of the model with the differences in the transition energies of the two emission bands of these phosphors.Zinc sulfide phosphors coactivated with Group III elements of the Periodic Table have been reported to have a long wave-length emission band in addition to the short wave-length emission band associated with activation by Group I elements and with self-activation. KrSger and Dikhoff (1), for example, reported long wave-length emission in phosphors coactivated with Sc, Ga, or In. The emission bands peaked at 5250A with Sc, 5700A with Ga, and 6800A with In and were relatively independent of the identity of the activator. They also observed that the substitution of ZnS in part by CdS had less effect on the long wave-length emission spectra than on the short wave-length emission spectra. Klasens (2) attributed these long wave-length bands to the radiative recombination of a free hole with an electron trapped at the coactivator. Froelich (3) reported long wave-length emission for Cu and self-activated ZnS phosphors which were coactivated with quite high concentrations of A1. Emission peaks are at 5880 and 5000A, respectively. Apple (4) has reported that the crystalline structure influences the relative intensities of the two emission bands observed with ZnS: x(Cu, Ag, Au), y(Ga, In) phosphors in which x K y. The long wave-length emission was found to be enhanced in hexagonal ZnS. He has suggested that this effect may be related to a change in association of activator and coactivator.In this investigation a comprehensive study of ZnS:x(Cu or Ag), y(Ga or In) was made. The spectra of the long wave-length emission are found to depend on the identities of both activator and coactivator. The relative intensities of the long and short wave-length emission depend on concentrations of activator and coactivator and on temperature of excitation. These experimental results are explained by means of a model for the long wavelength emission center consisting of a highly associated activator-coactivator center. This center is similar to the associated donor-acceptor system proposed by Prener and Williams (5) to explain the short wave-length emission by radiative transitions from excited states of the donor to the ground state of the acceptor but is different in that the donor and acceptor responsible for the...

“…ZnS:Dy, CL-- Figure 6 shows the EL emission spectra of a The spectra observed for ZnS:RE, C1 differ generally in the relative intensity of the lines from those observed from the bare RE ions in ZnS (17,18). This is true in some cases for REF3 dopants also (1).…”

Section: Device Performance and El Emission Spectramentioning

confidence: 95%

AC Thin Film Electroluminescent Devices with Rare Earth Doped ZnS

Dr.Jayaraj¹,

Vallabhan²

1991

The fabrication of ZnS:Re, C1 thin-film electroluminescent (TFEL) devices and their emission characteristics are described. The various emission bands and lines observed in the spectra are assigned to the transitions within the RE 3~ ions. The operating voltages have been brought down below 50 V using devices with metal-insulator-semiconductor structure, with Sm203 as the insulator. Studies on the effect of halides (F-, CI-, Br-) and oxide (O~) on the EL emission spectra of ZnS:Pr TFEL devices show that the fluoride dopant produces the maximum brightness. The brightest of the ZnS:Re, CI devices studied, ZnS:Tb, C1, has a brightness of about 500 fL, about one-third that of a typical ZnS:Mn EL celt.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.126.162.126 Downloaded on 2015-03-14 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.126.162.126 Downloaded on 2015-03-14 to IP