Evidence for reversible photostructural change in local order of amorphous As2S3 film

As₂S₃ films were exposed to band-gap illumination both at 290 and 77 K alternately, and after each exposure optical and X-ray measurements were carried out. It has been clarified that the reversible photodarkening should be attributed to the reversible change in local order of the network.     

Reversible photostructural change in melt-quenched As2S3 glass

Reversible phtodarkening and photostructural change accomplished by repeated cycles of band-gap illumination and annealing have been observed in melt-quenched As₂S₃ glass for the first time. The magnitudes of photo-induced shift of optical absorption edge as well as the fraction of photo-expansion observed in melt-quenched As₂S₃ glass coincide quantitatively with those observed in well-annealed evaporated As₂S₃ glass. The experimental data involving results of crystalline As₂S₃ demonstrate that the reversible photostructural change is “unique” to amorphous state and is not affected by the difference in disordered structure originated from preparation technique.     

Thin films of As2Se3 synthesized by spin-coating

Thin films of amorphous As₂Se₃ were synthesized by spin-coating a solution of an amine salt in thioacetamide on a thoroughly cleaned flat soda glass substrate. Films up to 0.68 μm thick were obtained. Electrical properties and optical absorption coefficient data were measured. The conductivity is of the same order of magnitude as those of evaporated and melt-quenched films. An exponential inverse-temperature law is observed for the variations in electrical conductivity. The optical absorption results indicate that the absorption edge of the synthesized a-As₂Se₃ films is due to an allowed direct transition of energy about 1.77 eV.     

单晶LiNbO3:Mn2+的ESR谱研究

用室温电子自旋共振（ESR）实验研究单晶LiNbO3中Mn2+的精细结构和超精细结构.对ESR谱的分析得出,零磁场的能级分裂数值：自旋角动量能级±12〉与±32〉之间的间隔为Δε1=-587×10-4cm-1,而±32〉与±52〉之间的能级间隔为Δε2=-2633×10-4cm-1；其各向异性朗德因子g∥=21810，g⊥=20937；精细结构常数D=-536×10-4cm-1；超精细结构常数A∥=8836×10-4cm-1，A⊥=8120×10-4cm-1，即精细结构相互作用要比超精细结构相互作用大得多.另外，特别值得提到的是实验中还发现两组明显的禁戒跃迁，-32〉12〉和-12〉52〉. 关键词： 单晶 精细结构 超精细结构 禁戒跃迁     

Effect of age in vitreous As2Se3 thin films

In this paper are reported the studies of structural changes developed in the photoconductivity response spectrum of amorphous As₂Se₃ thin films with their age. Thin films were prepared by the thermal evaporation of amorphous As₂Se₃. Also reported are the X-ray diffraction studies. An explanation of the phenomenon in terms of structural changes has been attempted.     

Fluorescence of Mn2+ in CaCO3

The fluorescence of Mn²⁺ ion as impurity in CaCO₃ has been investigated. Emission bands from the ⁴D(E_g), ⁴D(T_2g) and ⁴G(T_1g) levels have been observed. The analysis of excitation and emission spectra has allowed to obtain the values of field strength (Dq) for the excited energy levels of Mn²⁺ in CaCO₃ lattice. The temperature dependence of excitation and emission spectra yield an activation energy for thermal quenching of luminescence very close to theoretical calculation. The behaviour of luminescence lifetime with temperature has also been obtained.     

ESR study of Fe3+ and Mn2+ ions on trigonal sites in ilmenite structure MgTiO3

Electron spin resonance has been observed for Fe³⁺ and Mn²⁺ ions occupying sites with trigonal symmetry in undoped and doped Verneuil-grown crystals of the ilmenite type compound MgTiO₃. At 300 K, the fine structure parameters in the spin Hamiltonian are (in 10^?4cm^?1) D = +844 (± 1), (a? F) = +118 (± 1), a = 69 (± 7) for Fe³⁺ and D = +164 (± 1), (a ? F) = +10.2 (± l), a = 7.0 (± 1) for Mn²⁺. These values are compared with literature data for Fe³⁺ and Mn²⁺ in other oxides, especially Al₂o₃, with particular reference to the recent “superposition” theory of the effect of a trigonal distortion. From the orientation of the axes of cubic pseudosymmetry of the spin Hamiltonian, and with the assumption that a has the same sign for both ions, it is proposed that Fe³⁺ and Mn²⁺ occupy the same octahedral site, namely the Mg²⁺ site. Anomalous line splittings observed for one sample were attributed to twinning on (0001) or {1120} planes.     

The thermal activation energy of crystalline As2Se3

The conductivity of As₂Se₃ single crystals has been measured, both 6 b and ⊥ b, in the temperature range 300–400°K. Thermal activation energies of 0.94 and 1.1 eV were obtained for H₂ and I₂-grown crystals, respectively.     

Reversible photo-induced volume changes in evaporated As2S3 and As4Se5Ge1 films

Reversible photo-induced volume changes have been observed accompanying reversible optical absorption edge shift produced by successive cycles of band gap illumination and annealing for well-annealed evaporated As₂S₃ and As₄Se₅Ge₁ films. The As₂S₃ film shows an increase in its volume by illumination, while As₄Se₅Ge₁ film shows a decrease. Qualitative discussion has been given in connection with pressure-induced optical constant change.     

ESR in X-irradiated As2O3 glass

X-irradiation of glassy As₂O₃ at 77K or 300K produces an unusually large density (～5×10¹⁸ cm^-3) of paramagnetic centers which are stable at 300K. The average spin-Hamiltonian parameters (g = 1.998, g_⊥ = 1.984, A₆ = 243G, A_⊥ = 114G) indicate that these centers are analogous to those previously observed in As₂Se₃ and As₂S₃ glasses and that they consist of unpaired electrons localized on a non-bonding 4p orbital of an As atom. Unlike the results obtained for As₂Se₃ and As₂S₃, the concommitant holes in As₂O₃ are trapped on Fe²⁺ impurity sites which become Fe³⁺ and not on non-bonding oxygen p orbitals. The radiation induced ESR is also accompanied by a stable optical absorption tail which lies within the band gap and increases exponentially with energy. This absorption can be partially bleached with the application of sub-band-gap light.     

High-frequency dielectric properties of glassy As2Se3

The dielectric properties and the ac conductivity of glassy As₂Se₃ have been obtained for a wide frequency range at temperatures between 80 and 300 K. The results are described in terms of a non-Debye-type dielectric response due to a coupling of a polarization response to structural modes.     

ESR of Mn2+ in La2O3: Position and intensity of forbidden hyperfine lines

Position and intensity of (ΔM=1, Δm=1) forbidden hyperfine lines arising in the central transition of the Mn²⁺:La₂O₃ ESR spectrum are analyzed by means of the existing theories. This permitted us to determine the quadrupole coupling constant and the nuclear Zeeman term.     

ESR study of Mn2+ in sodium β″-alumina

ESR measurements are reported on Mn²⁺ diffused into sodium β″-alumina. The spin Hamiltonian parameters obtained are g₁₁ = 2.0000(2), $\text{g}{}_{\mathrm{?}}\text{= 2.0019(2)}$, A₁₁ = ?8.39(3) mT, $\text{A}{}_{\mathrm{?}}\text{= ?8.33(3)}\text{mT}$ and D = ?7.20(5) mT. The site position of the Mn²⁺ ions is discussed and compared to published results for Mn²⁺ in sodium β-alumina.     

Interrelation between glass transition and reversible photostructural change in a-As2S3

The optical absorption edge has been observed to make a parallel shift to lower energy in a-As₂S₃ as the glass transition temperature, T_g, increases. The structural difference corresponding to different T_g and reversible photostructural change give the same linear relation between the edge shift and the volume change. The saturated position of the edge after long time illumination or annealing is determined only by the condition of last treatment and is independent of previous history. These results suggest that both structural changes are of the same kind and that in the glass there exists an equilibrium state under illumination, if crystallization is avoided.     

Spectral distribution of steady-state photoconductivity in amorphous As2Se3

The spectral distribution of steady-state photoconductivity has been examined for a series of bulk and evaporated samples of amorphous As₂Se₃. All bulk samples, irrespective of preparation technique or sample treatment, show a distinct shoulder in the photocurrent spectral distribution at energies near 1.4 eV. This feature is interpreted as spectroscopic evidence for the existence of a well-defined defect level in the gap of amorphous As₂Se₃. Evaporated As₂Se₃ films do not show any structure in the spectral response.     

ESR of Fe3+ -Rhombic,Fe2+ -Vo and Fe1+ -Vo complexes in SrTiO3

Three new Fe-defect complexes have been identified by ESR in Fe doped crystals of SrTiO₃. These are an Fe³⁺ center with rhombic fine structure in the “as-grown” crystals, and the vacancy associated complexes Fe²⁺ -V_o and Fe¹⁺ -V_o in “reduced” crystals. Photo-excited charge transfer effects are observed for these centers.     

Temperature dependence of the ESR spectra of Mn2+ in iron pyrite (FeS2)

The first observation of the ESR spectra of Mn²⁺, entering substitutionally for Fe²⁺ in the Van Vleck paramagnet FeS₂ (polycrystals), is reported. The data from 5 to 295 K fits the spin-Hamiltonian $\text{h}{}_{\mathrm{s}}\text{= gβ}\text{H}\text{·}\text{S}$ + $\text{[S}{}^{\mathrm{<mtext>2</mtext>}}{}_{\mathrm{z}}\text{?}\text{1}\text{3}\text{S(S + 1)] + A}\text{S}\text{·}\text{I}$, with g = 2.000 ± 0.001, A/β = ?95.0 ± 0.5 Oe and D/β varying from 50 Oe (5K) to 59 Oe (295 K). The temperature dependence of D can be described in terms of a single phonon-mode with frequency ? 145 cm^?1.     

Enhancement of hole drift velocity in amorphous As2Se3 by iodine doping

The addition of ～ 0.6 at.% iodine to approximately stoichiometric a-As₂Se₃ enhances the hole drift velocity by more than a decade but does not affect its field, thickness and temperature dependence or the degree of disorder. It is speculated that iodine reduces the ratio of trapping to hopping states in the trap-controlled hopping process which recently has been proposed for a-As₂Se₃.     

近红外到近红外Mn2+掺杂NaYF4:Yb3+/Tm3+纳米粒子的制备及其生物成像

在反应温度为200℃、反应时间为8 h的温和条件下,采用水热法合成了近红外到近红外的Mn²⁺掺杂NaYF₄:Yb³⁺/Tm³⁺上转换荧光纳米粒子,再以两亲性聚合物C₁₈PMH-mPEG作为亲水性配体修饰到上转换荧光纳米粒子表面,得到具有水溶性的上转换荧光纳米粒子。然后在980 nm近红外光源激发下,测量了上转换荧光纳米粒子的荧光发射光谱,在（800±10） nm附近,观察到了较强的单近红外光发射（³H₄→³H₆）。对样品进行细胞毒性实验,结果表明制得的水溶性Mn²⁺掺杂NaYF₄:Yb³⁺/Tm³⁺纳米粒子具有良好的生物相容性。并进一步在小鼠体内进行了近红外成像,表明其在生物成像领域将会具有一定的应用前景。     

Structure, thermally and optically induced effects in amorphous As2Se3 films prepared by pulsed laser deposition

Thin amorphous As-Se films were prepared by pulsed laser deposition (PLD) and by classical thermal evaporation techniques. Raman spectra and optical properties (optical gap, E_g^opt, index of refraction, n, third-order non-linear susceptibility, χ⁽³⁾) of prepared films and their photo- and thermally induced changes were studied. The structure of laser deposited films was close to the corresponding bulk glasses contrary to thermal evaporated films. The composition of PLD films was practically unchanged during the process of deposition. The optically and thermally induced changes of n and of E_g^opt in PLD films are different from the changes in thermally deposited films. The differences are discussed.