Luminescent crystals of MIIGa2S4:Er3+ (MII = Eu, Yb, Ca)

Abstract

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...

Исследование явления токопрохождения в кристаллах EuGa-=SUB=-2-=/SUB=-S-=SUB=-4-=/SUB=-:Er-=SUP=-3+-=/SUP=-

“…10.55424.19517 С момента получения тетрахалькогенидов европия EuGa 2 S 4 из группы AB III 2 C VI 4 (A -Eu, Yb, Dy; B -Ga, In; C -S, Se, Te) с незаполненными внутренними 4 f -оболочками, активированных редкоземельными элементами, в частности эрбием, начались их интенсивные исследования, в ходе которых были выявлены их многие интересные физические свойства. Фото-, электрои термолюминесцентным свойствам этих кристаллов посвящено значительное число работ [1][2][3][4][5][6], экспериментальные результаты которых позволили определить ряд важных параметров фотолюминесценции (красное смещение, стоксово смещение, время жизни ионов Er 3+ и др. ), электролюминесценции и термолюминесценции (частотный фактор, энергия активации, сечение захвата, концентрация ловушечных уровней и др.).…”

Investigation of the phenomenon of current transition EuGa-=SUB=-2-=/SUB=-S-=SUB=-4-=/SUB=-:Er-=SUP=-3+-=/SUP=- crystals

“…Europium tetrachalcogenides EuGa 2 S 4 from group AB III 2 C VI 4 (A -Eu, Yb, Dy; B -Ga, In; C -S, Se, Te) with an incomplete inner 4 f shell, which are activated by rare-earth elements (specifically, erbium), have been studied extensively since the moment of their synthesis, and several intriguing physical properties have been revealed in the process. A considerable number of papers [1][2][3][4][5][6] focused on the photo-, electro-, and thermoluminescence properties of these crystals have already been published. The results of experiments performed in these studies provided an opportunity to determine certain key parameters of photoluminescence (red shift, Stokes shift, lifetime of Er 3+ ions, etc.…”