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The absorption spectra of RbCu2Cl3 and Rb2Cu3Cl5 thin films were studied in the 2−6 eV spectral and 90−450 K temperature ranges. The localization of excitons in CuCl 4 3 − structural elements of crystal lattice of compounds, three-dimensional nature of excitons in RbCu2Cl3 and two-dimensional nature of excitons in Rb2Cu3Cl5 were established. The exciton spectra of RbCu2Cl3 and Rb2Cu3Cl5 thin films were interpreted based on the transitions in the Cu+ ion. [ABSTRACT FROM AUTHOR]

The exciton spectra of Cs1–xRbxPbCl3 solid solution thin films are studied in a range of 2–6 eV. The formation of solid solutions stable at room temperature was detected in range of concentrations 0 ≤ х ≤ 0.7. A linear dependence of the exciton band and bandgap width parameters on the concentration was found. Kinks are observed along the temperature dependences of the spectral position Em(T) (x > 0) of the long-wave exciton band at 310 and 320 K that are characteristic of second-order phase transitions. The exciton excitations in CsPbCl3 are found to have a three-dimensional nature, while in Cs1–xRbxPbCl3 (x > 0) solid solutions they are found to be two-dimensional. [ABSTRACT FROM AUTHOR]

The absorption spectra of thin films of KPb2(Cl1-xBrx)5 (0 ≤ x ≤1) are studied in the spectral range of 2-6 eV (T=90 K). Solid solutions with a mixed monoclinic structure are formed at all concentrations 0 ≤x≤ 1 and a tetragonal structure is found for 0.9≤ x ≤ 1. The temperature of the tetragonal to monoclinic phase transition in the solid solutions increases with the amount of Cl additive. The concentration dependences of the spectral location and half width of the long-wavelength exciton bands are the result of small-scale and large-scale fluctuations in the composition of the solid solution. [ABSTRACT FROM AUTHOR]

A study of the absorption spectrum of thin CuPb2Br7 films in the 2-6 eV spectral and 90-500K temperature ranges. It is shown that the exciton spectrum of the compound is associated with transitions in the lead ion. The temperature dependence of the spectral position and half-width of the low-frequency exciton band contains features associated with phase transitions γ → β (Tc1 = 159 K) and β → α (Tc2 = 434 K) and the disordering of the cation sublattice of the compound in the transition to the superionic state. [ABSTRACT FROM AUTHOR]

A study of the absorption spectrum of thin KPb2Cl5 films, in the spectral range of 2-6 eV, within the temperature interval 90-520 K. It is found that low-frequency exciton states are localized in the sublattice of the compound containing the Pb2+ ions, and that they are excitons of intermediate coupling having a two-dimensional nature. [ABSTRACT FROM AUTHOR]

The absorption spectrum of thin film CsPbCl3 in the 2-6 eV range is studied at temperatures of 90-500 K. Sudden changes show up in the temperature dependences of the parameters of the long-wavelength exciton band (spectral position Em(T), half width Γ(T), and oscillator strength f(T)) at the first order phase transitions at 310 and 320. No phase transitions in Em(T), Γ(T), and f(T) are detected at low temperatures. The exciton excitations in CsPbCl3 are found to have a three-dimensional character. [ABSTRACT FROM AUTHOR]

The excitonic absorption spectra of thin films of ferroelectric Cs2CdI4 and Cs2ZnI4 solid solutions are studied for the first time. It is found that, within the whole range of molar concentrations x, the spectra of Cs2(Cd1 − xZn x)I4 comprise two bands that originate from the bands of the two compounds. It is shown that the exciton transfer occurs most efficiently between the tetrahedrons CdI4 and ZnI4 along the b axis of the crystal. Unusual behavior of the concentration with regards to the maxima of long-wavelength excitonic bands E m( x) agrees well with the developed theory that takes into account dependence on x of the matrix element of the intertetrahedron exciton transfer and that is similar to the theory of Davydov’s splitting in molecular crystals. [ABSTRACT FROM AUTHOR]

The excitonic absorption spectra of thin films of the solid solutions Rb2(Cd1-xZnx)I4 have been studied for the first time. It is determined that the spectra of the solid solutions are stable and consist of two bands which genetically originate from the initial bands of the compounds Rb2CdI4 and Rb2ZnI4. It is shown on the basis of the structure of the crystal lattices of the compounds that the concentration dependence of the spectral position of the excitonic bands AI and AII is related with the transfer of excitons between CdI4 and ZnI4 tetrahedra along the b axis of the solid solutions. The experimental result is in good agreement with the calculation of the energies EAI(x) and EAII(x) on the basis of a theory similar to the theory of Davydov splitting of excitonic bands in molecular crystals. [ABSTRACT FROM AUTHOR]

The absorption spectrum of thin K2ZnI4 films has been investigated in the range of 3–6 eV at temperatures from 90 to 340 K. It is established that this compound belongs to direct-gap insulators; low-frequency exciton excitations are localized in the ZnI4 lattice layers and have a quasi-two-dimensional character. The spectral analysis revealed the existence of two K2ZnI4 modifications, which presumably belong to the monoclinic (I) and orthorhombic (II) phases. The temperature dependences of the spectral position and halfwidth of the low-frequency exciton band in K2ZnI4 revealed the existence of first-order phase transitions at 215 and 225 K in the monoclinic and orthorhombic phases, respectively. [ABSTRACT FROM AUTHOR]

The absorption spectrum of Rb2ZnI4 thin films in the spectral region 3–6 eV is investigated in the temperature range 90–290 K. It is found that the compound is a direct-gap insulator and that the low-frequency excitations are localized in the ZnI42- structural layers of the crystal lattice and are of a quasi-two-dimensional character. For T<200K the temperature dependence of the spectral absorption and the half-widths of the long-wavelength exciton band exhibits thermal memory effects due to precursors of the low-temperature phases. [ABSTRACT FROM AUTHOR]

The absorption spectrum of Cs2ZnI4 thin films in the energy range 3–6 eV at temperatures from 90 to 340 K has been investigated. It is established that this compound belongs to direct-gap insulators. Low-frequency exciton excitations are localized in ZnI4 structural elements of the lattice. Phase transitions at 280 K (paraelectric phase ↔ incommensurate phase), 135 K (incommensurate phase ↔ monoclinic ferroelastic phase), and 96 K (monoclinic phase ↔ triclinic ferroelastic phase) have been found from the temperature dependences of the spectral position and halfwidth of the low-frequency exciton band. Additional broadening of the exciton band is observed for ferroelastic phases; it is likely to be due to exciton scattering from strain fluctuations near domain walls. [ABSTRACT FROM AUTHOR]

A study is made of the excitonic absorption spectra of solid solutions of the system (KI)2–(1-x)AgI–xCuI. On the basis of the dependence of the parameters of the excitonic bands on the concentration x, it is established that solid solutions of the type K2Ag1-xCuxI3 are formed in the range 0≤x≤0.2. Substitution of Ag atoms by Cu atoms in the AgI42- tetrahedra, which form chains in the orthorhombic crystal K2AgI3, promotes the formation of quasi-1D exciton bands and spectra of the persistence type, according to the Onodera–Toyozawa classification, with a splitting off of the impurity band from the exciton band. Comparison with the results of studies of the excitonic spectra in solid solutions Rb2Ag1-xCuxI3 and Cs2Ag1-xCuxI3 attests to the appearance of the Rashba effect at small x and to qualitative agreement with the Onodera–Toyozawa theory. [ABSTRACT FROM AUTHOR]

The absorption spectrum of thin films of solid solutions of RbxK1 – xAg4I5 superionic conductors is investigated in the energy range 3–6 eV at temperatures from 90 to 290 K upon heating and cooling. It is established that the temperature dependences of the spectral position Em and the half-width Γ of the long-wavelength exciton band are determined by the exciton–phonon interaction and the generation of Frenkel defects at phase transitions to the superionic state. Fluctuations of the composition of solid solutions do not affect the behavior of the dependences Em(x) and Γ(x) at 90 K, which is indicative of the localization of excitons in the AgI sublattice of these compounds. A difference in the dependences Tc1(x) and Tc2(x) (the γ→β and β→α phase transitions, respectively) is revealed: the curve Tc1(x) has a minimum at x≈0.5, whereas the curve Tc2(x) shows a weak maximum. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]