Ba3La(BO3)3基质中Tb3+的光致发光

以高温固相法合成了Ba3La(BO3)3∶Tb3 发光材料。在254nm紫外光激发下,研究了Ba3La(BO3)3∶Tb3 的激发光谱、发射光谱、发光强度与Tb3 浓度的关系。确定了Ba3La(BO3)3基质中Tb3 的自身浓度猝灭机理;探讨了助熔剂LiCO、敏化剂Ce3 、Bi3 的加入对荧光粉的发光强度的影响。     

Hyperfine suppression of 2 3 S 1--3 3 P J transitions in 3He

Two anomalously weak transitions within the 2(3)S_(1)--3(3)P_(J) manifolds in 3He have been identified. Their transition strengths are measured to be 1000 times weaker than that of the strongest transition in the same group. This dramatic suppression of transition strengths is due to the dominance of the hyperfine interaction over the fine-structure interaction. An alternative selection rule based on IS coupling (where the nuclear spin is first coupled to the total electron spin) is proposed. This provides qualitative understanding of the transition strengths. It is shown that the small deviations from the IS coupling model are fully accounted for by an exact diagonalization of the strongly interacting states.     

Absorptionsspektren von Er3+ in InCl3 und in ScCl3

The optical absorption spectra of Er³⁺ in single crystals of InCl₃ and ScCl₃ have been obtained between 14,000 and 29,000 cm^?1. The observed crystal field splittings are interpreted in terms of crystal potential of symmetry 3m for ScCl₃ and of symmetry 2m for InCl₃. There is however found, that for both cases the splittings will be approximately explained by a crystal potential of cubic symmetry. The employed hostlattices are of special interest, because the ions of the iron series can occupy the same sites as the rare earth ions.     

Er3+/Yb3+共掺LiNbO3晶体中Er3+的光谱特性分析

在室温下,测量了采用Czochralski方法生长的as-grown和经退火处理的Z切Er^3＋／Yb^3＋共掺同成分LiNbO3晶体的α偏振吸收光谱（300-1650nm）。运用Judd—Ofelt理论对该晶体中Er^3＋的光谱特性进行了分析。由所测得的吸收系数的积分计算得到了从基态到激发态的若干个主要的电子跃迁强度实验值。利用最小二乘法确定出Er^3＋／Yb^3＋共掺LiNbO3晶体中Er^3＋的Judd-Ofelt参数。进而确定了自发辐射概率,从激发态能级到其各个下能级的荧光分支比以及能级辐射寿命。此外,还讨论了Yb^3＋的共掺和退火处理对LiNbO3晶体中Er^3＋光谱特性的影响。     

Mössbauer study of Er3+ in ErH3 and YH3

The Mössbauer spectra of ¹⁶⁶Er in ErH₃ and YH₃ have been measured. Using and axial Hamiltonian, the electronic gyromagnetic rations for the ground state of Er³⁺ in YH₃ have been deduced: g| = 11.6 ± 0.1 and g⊥ = 4.4 ± 0.1. The analysis yields crystal field parameters which provide the correct λ₇ ground state with these g-values.     

EPR of Er3+, Nd3+, and Ce3+ ions in YAlO3 single crystals

EPR spectra of the Er³⁺, Nd³⁺, and Ce³⁺ ions substituting for the Y³⁺ ion in the YAlO₃ yttrium orthoaluminate lattice are studied. The EPR spectra of these rare-earth ions are described by a spin Hamiltonian of rhombic symmetry with an effective spin S=1/2. The principal values of the g tensors were determined from an analysis of the angular dependences of the EPR spectra. The orientation of the local magnetic axes of paramagnetic centers relative to the YAlO₃ crystallographic directions are shown to depend on the actual rare-earth species. The EPR spectra exhibit a hyperfine structure due to the ¹⁶⁷Er, ¹⁴³Nd, and ¹⁴⁵Nd odd isotopes, which permitted unambiguous identification of these spectra. The hyperfine coupling constants for the odd erbium and neodymium isotopes are determined.     

Nonhydrogenic exciton spectrum in perovskite CH3NH3PbI3

The excitons in the orthorhombic phase of the perovskite CH₃NH₃PbI₃ are studied using the effective mass approximation. The electron–hole interaction is screened by a distance‐dependent dielectric function, as described by the Haken potential or the Pollmann–Büttner potential. The energy spectrum and the eigenfunctions are calculated for both cases. The results show that the Pollmann–Büttner model, using the corresponding parameters obtained from ab initio calculations, provides better agreement with the experimental results.

     

Structural phase transitions in (CH3)3NHCdCl3

The structure of (CH₃)₃NHCdCl₃ has been determined by single crystal X-ray diffraction at 174K. Phase changes around 342, 374, and 415 K have been detected by DTA and have been correlated with the dynamics of the organic groups via NMR measurements. No change of Laue symmetry has been observed between 170 and 400 K.     

偏硅酸钙中Pr3+的4f5d态的光谱特性及Pr3+→Gd3+的能量传递

合成了高效发射UV光的CaSiO3:Pr^3 新型荧光体，研究了室温下Pr^3 的4f5d态的发射和激发光谱，Pr^3 的4f5d态的最低子能级向4f^2组态的^3H4，^3H6和^1G4能级跃迁产生UV发射，并不伴随有4f-4f能级跃迁的可见光发射。Pr^3 的浓度猝灭是由于辐射和无辐射能量传递造成的，同时，在CaSiO3中，存在Pr^3 →Cd^3 的能量传递，探讨了其能量传递特性。     

Terahertz Vibrational Modes in CH3NH3PbI3 and CsPbI3 Perovskite Films

JETP Letters - Films of CH3NH3PbI3 organometallic perovskite, which is currently considered as a promising basic material for new-generation solar cells, as well as films containing CsPbI3...     

EPR of Pb3+ ion in LiBaF3 crystals

Complex EPR spectra of paramagnetic centers Pb³⁺ formed in LiBaF₃:Pb²⁺ crystals under X-ray irradiation are studied in the temperature range of 10–150 K. It is shown that lead ions substitute Ba²⁺ ions in the LiBaF₃ crystal and are in the cubic-octahedral 12-fold environment of the fluorine ions. The hyperfine structure constants describing the observed spectrum are determined and parameters of superhyperfine interaction with the nearest fluorine ions are estimated.     

The role of CeF3 in LaCl3 scintillation crystal

The properties of LaCl₃:CeF₃ crystal are investigated and its hydroscopic nature has a much more decrease than that of LaCl₃:CeCl₃ crystal. The scintillation properties of LaCl₃:CeF₃ maintain as excellent as that of LaCl₃:CeCl₃. The LaCl₃:CeF₃ crystal has a good optical transmittance without obvious optical absorption bands between 322 and 800 nm, and has the same absorption edge as the LaCl₃:CeCl₃ crystal (about 315 nm). Its emission spectra, decay time and light yield are the same as the LaCl₃:CeCl₃.     

Study of phase coexistence in YVO3 and LaVO3

The coexistence at low temperature in YVO₃ and LaVO₃ of two competing phases with defined orbital and spin orientations is studied by Raman spectroscopy. The temperature evolution of the phonons indicates that phase coexistence, due to strain in YVO₃ and fluctuations in LaVO₃, is not restricted to small R ionic radius in RVO₃ compounds. Also, a typical temperature at 50 K is inferred from the temperature dependence of the intensities in LaVO₃. Copyright © 2015 John Wiley & Sons, Ltd.     

ESR of O-3 trapped in γ-irradiated NaClO3

The ESR spectra of γ-irradiated NaClO₃ was analysed at Q-Band, between 110 to 300 K. The single crystals were annealed at 180° C until the spectra indicated the presence of only one paramagnetic center. This center was indentified as the ozonide O^-₃ with $\text{g}\text{}\text{= 2.007±0.001}$, $\text{g}\text{⊥}\text{= 2.010±0.001}$ and g_av=2.009. Four magnetically inequivalent sites per unit cell with symmetry axes along the cube diagonals were observed. The axial symmetry found for the g-tensor was interpreted in terms of molecule rotation around the trigonal axes. A rotational frequency of 2×10⁹ c/s and an activation energy of 10 mev for the rotational motion could be estimated.     

Optical characterization of Cr3+ centers in LiNbO3

Low-temperature luminescence spectra of stoichiometric Cr:LiNbO₃, congruent Cr:LiNbO₃ and congruent Cr,Mg:LiNbO₃ were studied. Dominant low-field and minor high-crystal-field optical centers are the Cr³⁺ impurity ions that preferentially occupy Li⁺ sites (Cr_Li) in the Cr:LiNbO₃ crystals. Low-field centers related to Cr³⁺ substitution of Nb⁵⁺ (Cr_Nb) occur in addition to Cr_Li in co-doped Cr,Mg:LiNbO₃ samples. Application of high hydrostatic pressure leads to the transformation of dominant Cr³⁺ centers from low- to high-field type due to strong pressure-induced blue shift of the ⁴ T ₂ state, resulting in its crossing with the ² E state of Cr³⁺. This level-crossing effect was observed for the dominant Cr³⁺ _Li and Cr³⁺ _Nb centers at pressures that correlate well with estimations based on the ⁴ T ₂-² Eenergy gap (230 cm^-1 and 1160 cm^-1) and on the rate of their pressure-induced change (14.35 and 11.4 cm^-1/kbar, respectively). We also studied inhomogeneous broadeningof the ² E?⁴ A ₂transitions at ambient pressure for the minor high-field “defect” Cr³⁺ _Li centers in congruent LiNbO₃. A fine structure in the spectral response of these centers was observed. The obtained results are discussed on the basis of a microscopic hierarchic model for perturbed Cr³⁺ ions in the LiNbO₃ lattice. Received: 25 June 2001 / Published online: 2 November 2001     

Anisotropy of Magnetic Properties in Single Crystals of CH3NH3PbI3 Hybrid Perovskites

JETP Letters - Hybrid metal-organic CH3NH3PbI3 perovskites are promising materials for photovoltaics and optoelectronics, and the recently discovered magnetic and electrical ordering in them...