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We present the results of a study of the luminescence and luminescence excitation spectra, and also the luminescence kinetics of a BaSiO 3 :Yb 3+ crystal. We have established the mechanism for emission by the matrix and energy transfer from the matrix to the rare earth ion.Introduction. In a study of a series of sections in the system BaO-SiO 2 -GeO 2 , the authors of [1, 2] indicated the possibility of the existence of broad regions of substitutional solid solutions between compounds of analogous composition. The compound BaSiO 3 crystallizes in two polymorphic varieties, with a ring structure (pseudowollastonite, a = 7.50 Å, c = 10.58 Å) and a chain structure (pyroxenoid, a = 4.54 Å, b = 5.56 Å, c = 12.27 Å). In solidphase synthesis, BaSiO 3 is crystallized in the chain polymorphic form. The ring form of BaSiO 3 was synthesized for the first time by the hydrothermal method in [3]. In [4], the crystal phases and luminescent properties were studied for the ternary system SrO-BaO-SiO 2 , activated by Ce 3+ ions. The excitation spectrum consists of three bands with maxima at 190 nm, 230 nm, and 320 nm, and in the emission spectrum there are maxima at 392 nm and 475 nm, associated with Ce 3+ ions. In [4], an effect from different compensation charges on the excitation and emission spectra was also demonstrated.Review of literature data shows that the luminescent properties of a BaSiO 3 crystal activated by Yb 3+ ions have not been studied. In [5], results are presented from an investigation of luminescence of Eu 2+ ions in SrSiO 3 and CaSiO 3 crystals that are isostructural to the BaSiO 3 crystal (for SrSiO 3 :Eu 2+ and CaSiO 3 :Eu 2+ at 4.2 K, the emission maxima are found at 440 nm and 465 nm). In [6], a broad band with maximum at 550 nm is observed in the emission spectrum of a BaSiO 3 :Eu 2+ crystal. When the temperature is raised from 4.2 K to room temperature, a shift of the emission maximum is observed, from 550 nm to 575 nm. The halfwidth of the emission band also increases, but at 90 K it suddenly decreases. When the temperature again increases, the halfwidth increases. The authors of [6] asssociated such behavior of the temperature dependence of the halfwidth with a phase transition in the BaSiO 3 :Eu 2+ crystal. The luminescent properties of metal silicates MO-SiO 2 :Eu 2+ (where M is Ca, Sr, Ba) are considered in [7].As an activator for crystalline matrices, in many respects ytterbium occupies a special position among other rare earth elements. The Yb 3+ ion has a very simple system of electronic states, and no intermediate coupling problems arise in its calculation. The only term, 2 F, is split by spin-orbit coupling into two multiplets, spaced far apart (≈10000 cm -1 ). A feature of this level system is the fact that owing to the absence of close multiplets, when considering some electron-phonon coupling phenomena such as the temperature shift of phononless lines, for Yb 3+ ions we can consider mixing of only electronic states within the multiplets, and we can neglect intermultiplet mixing.The Yb 3+ io...

We have studied the photoluminescent properties of M II Ga 2 S 4 :Er 3+ polycrystals (M II = Eu, Yb, Ca) for excitation by radiation with λ = 976 nm as a function of temperature. The samples were obtained by solid-state reaction. We have studied the comparative characteristics of the anti-Stokes and IR luminescence of these luminophores. We have determined the mechanisms for anti-Stokes emission of M II Ga 2 S 4 :Er 3+ crystals.Introduction. Introducing the Er 3+ ion into a matrix leads to partial mixing of the 4f electron levels, shielded by the 5s and 5p shells [1]. As a result, rather distinct optical transitions within the 4f shell can be achieved in materials doped with Er 3+ . Transition from the first excited level ( 4 I 13/2 ) to the ground-state level ( 4 I 15/2 ) of the Er 3+ ion is accompanied by emission at the wavelength 1550 nm. In materials with a wide bandgap, the Er 3+ ion also emits several lines in the visible region of the spectrum. Due to the complicated energy level diagram, including some excited metastable levels, the multiple cooperative energy transfers and absorption processes occurring in the excited states of Er 3+ can be used for anti-Stokes luminescence. Conversion of IR emission to visible emission has been studied for different crystals and glasses doped with rare earth ions [2,3]. The ratio of the intensities of the visible and IR emission depends on the type of matrix material, the concentration of Er 3+ , and the excitation wavelength [4].Er 3+ -doped luminescent materials emitting at 1550 nm are of considerable interest for integrated thin-film technology for the conventional telecommunications C band (1530-1560 nm). Different dielectric thin-film materials doped with Er can be used for preparing planar optical amplifiers or lasers [5-9] that can be integrated into a communications system. On the other hand, the observed efficient anti-Stokes emission is promising for IR visualization purposes.IR luminescence of the Er 3+ ion in the 1550 nm region in calcium thiogallates CaGa 2 S 4 was first presented in [10]. Visible luminescence of CaGa 2 S 4 was studied earlier in [11].Interaction between Er 3+ ions leads to various cross-relaxation processes. In the case of thiogallates M II Ga 2 S 4 , in which multiphonon processes are weak, complete excitation of the 4 G 9/2 and 4 G 11/2 levels as a result of cross relaxation makes it possible to increase the population of the 2 H 11/2 and 4 S 3/2 levels. In thiogallate materials with low phonon energy [12], visible luminescence prevails under UV excitation conditions. The spectra of the doped samples are characterized by an absorption region where the energy is not much lower than the energy of the absorption edge for the matrix lattice due to charge transfer. The presence of a charge transfer region for the Er 3+ ion is quite unusual, and may be associated with the weak electronegativity of sulfur and the strong effective positive charge on the rare earth ion substituting for the M II cations.Thiogallate compounds of the type M II Ga 2...

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