Electronic-vibrational spectra of neodymium activated crystals

Abstract

17. H. Sobue, T. Uryu, K. Matsuzaki, and J. Tabata, "Stereoregularity of polymethacrylo- nitrile," J. Polym. Sci., l, No. 8, Part B, 409-411 (1963). 18. H. Herma, V. Groebe, and R. Schmolke, "Characterization of copolymers. 2. Composition and sequential length distribution of acrylonitrile--methacrylonitrile copolymers," Faserforsch. Textiltechnik, 117, No. 2, 56-60 (1966). ELECTRONIC-VIBRATIONAL SPECTRA OF NEODYMIUM ACTIVATED CRYSTALS V. F. Zolin, V. M. Markushev, V. I. Tsaryuk, and Ch. M. Briskina UDC 535.34:541.65 Electron vibrational (EV) spectra of neodymium (Nd ~+) compounds [I, 2] are interesting from different points of view. They could be useful in connection with investigations of the structure of luminescence centers [3-5]. The presence of EV bands can restrict the applica- bility of selective laser excitation spectroscopy in studying luminescence centers in dis- ordered media (for example, glasses) [6-8]. EV bands can make a considerable contribution to the overlap integrals of the luminescence spectra of donors and the absorption spectra of ac- ceptors, whose magnitude determines the probability of transferring exGitation energy in the luminescence quenching and sensitization processes, as well as with migration and cross- relaxation [9, 10]. Finally, the probabilities of multiphonon transitions, determining the rate of relaxation of excitation of luminescence centers in crystals and glasses activated by lanthanides, depends on the magnitude of EV interaction and the phonon density of states, which can be estimated from the EV spectra [11-13]. The EV spectra of europium and terbium compounds were studied in [4, 5, 14]. The inter- pretation of these spectra was facilitated by the relative simplicity of the Stark structure of the energy levels of the Eu 3+ ion and the similarity of the spectral properties of Eu ~+ and Tb s+. In this paper we present the results of investigations of EV s~ectra of analogous neodymium compounds, for which the EV interaction is stronger than for Eu + and Tb 3+. The use of laser excitation permitted observing easily the EV bands in the luminescence spectra of neo- dymium. The magnitudes of the EV interaction for the Nd s+ ion were estimated from the ratios of the integral intensities of the single-phonon and phononless bands (Io~/Ioo) [12]. Technique and Objects of Investigation. We investigated the spectra of materials used in laser technology: spectra of neodymium pentaphosphate NdPsO~, neodymium tetraphosphates and tetraphosphates of alkali metals MeNdP~O~ (Me = Na, K, Rh, Cs), binary molybdates with composition Na,La~-mNdm(MoO~)~ (m = l, 0.9, 0.25) and BaNda-mGdm(MoO~)~ (m = O, 1,8), binary tungstates Me~Lao.,Ndo.~(WO~)~ (Me = Na, Cs), calciumtungstates CaWOd, and garnets Y3AI2(A104)3 (YAG), Gd,Gaa(GaO~), (GGG), activated with 1% neodymium. Absorption spectra in the region 24,100-14,200 cm -~ were recorded photographically using an ISP-51 spectrograph with a long focal length UF-90 chamber and photoelectrically usin~ a DFS-12 spectrometer and F~U-79. The luminescence spectra in the region 9600-ii,700 cm , excited with a Rhodamine 6G tunable dye laser, were recorded by an MDR-23 monochromator using F~U-62 and a PAR 160 integrator. It is convenient to observe the single-phonon EV satellites, related to internal vibra- tions of ligands, in the absorption spectra of neodymium between bands of the electronic transitions ~I,/2--~G,/2 and ~I,/2--~G,/a, ~G5/2 and in the luminescence spectra between bands of the electronic transitions ~F,/a--~I,/~ and ~F~/a--~I~/2. EV satellites, generated by the transitions dIg/2--dGT/2~ 2G9/2, 2K~,/, and ~I,/a--~F,/,, ~S,/,, are also clearly evident. To separate the EV satellites and to identify them, we used the following: temperature dependence of the line intensities, comparison of EV spectra of different compounds with one another, as well as comparison with IR spectra and Raman scattering spectra, In a number of cases, it is useful to compare with EV spectra corresponding =o europium and terbium com- pounds. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 38, No. 4, pp. 614-620, April, 1983. Original article submitted February i, 1982. 448 0021-9037/83/3804-0448507.50 9 1983 Plenum Publishing Corporation