Red Electroluminescent (Zn, Cd)(S, Se)-Type Phosphors

Abstract

Red light emitting electroluminescent phosphors in the (Zn,Cd)(S,Se):Cu system were investigated. The best red electroluminescent phosphor is obtained by firing (0.9Zn,0.1Cd)(0.1S,0.9Se) adding Cu, 5 x 10 -3 g-atom/mole and the same coactivator concentration at 1000 ~ N ll00~ Electroluminescent and photoluminescent properties of phosphors of various composition were interpreted by curves illustrating the energy level variation with composition in solid solution, which is obtained by considering nearest-neighbor effects, and a temperature quenching factor in electroluminescence. From similar considerations, the variation of luminescent properties of phosphors of given composition, containing given luminescent centers, can be predicted, and the critical frequency of excitation when developing electroluminescent phosphors of a given color is presented.A (Zn,Cd) (S,Se) system as red light emitting electroluminescent (EL) phosphors has been developed for a part of its composition by Palilla and Baid (1), Matsuo et al. (2), Mironov and Markovskii (3), and Kolomoitsev et al. (4) in the course of our investigation, and earlier by Hegyi etal. (5), Larach et al. (6), Gelling et al. ( 7), and others, but it seems that a unified discussion on firing condition and EL properties has not been achieved. For example, the optimum firing condition differs from composition to composition, and parameters involved in EL characteristics vary with composition. Thus a question arises, "how shall we expect the possibility of (Zn,Cd)(S,Se) as long wavelength light emitting phosphors?" Solid solutions have been extensively prepared recently to change energy gap continuously for the purpose of matching the exciting or the emitting energy.In this system, a knowledge about the impurity energy level variation with composition as well as about the energy gap variation is indispensable, for the former is undoubtedly very sensitive to optical and electrical properties.In this paper we tried to give a systematic discussion on the above problem, and to give basic considerations on the impurity energy level variation in this system in connection with them.

Electroluminescent Properties of ZnSe-Type Phosphors

“…which is deduced theoretically by considering the supply of primary electrons, and the probability of impact ionization in the Mott-Schottky type barrier region (3), can explain the experimental results. A small deviation from [1] does not provide sufficient information to find out how primary electrons are supplied: tunneling from Cu2S phase, thermally or field ionization from donors; or current of backward biased diode. In the above consideration, the c-value can be expressed as follows c = a(f,T) + b(f,T)Ee [2] where Ee is the excitation energy and the first term is referred to the supply of the primary electrons, the second term to the ionization probability.…”

“…Phosphor preparation procedure has been described in another paper (1). Light emission from an EL cell in a vacuum chamber was measured using a Hitach EPU-2 type spectrometer and R136 photomultiplier.…”

Temperature dependence of effective thermal conductivity and effective thermal diffusivity of CdZnSe composite

“…Like wise CdZnSe is an n-type semi conducting wide band gap material having a direct band gap (Ray 1969, Bassam 1990) and hence is used as a window material. The full range of the ternary compound CdZnSe material was demonstrated as early as 1951 (Forgue et al 1951), and since then a small number of isolated studies concerned primarily with the preparation and use of CdZnSe as a phosphor have been reported (Lehman 1996, Haru et al 1968. The growth of ternary CdZnSe opens up the possibility of their applications in novel optoelectronic devices in the visible region of electromagnetic radiations (Gupta et al 1995).…”