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LAWS OF CRYSTAL-FIELD DISORDERNESS OF Ln3+ IONS IN INSULATING LASER CRYSTALS
A. Kaminskii
To cite this version:
A. Kaminskii. LAWS OF CRYSTAL-FIELD DISORDERNESS OF Ln3+ IONS IN INSULAT- ING LASER CRYSTALS. Journal de Physique Colloques, 1987, 48 (C7), pp.C7-359-C7-362.
�10.1051/jphyscol:1987786�. �jpa-00227090�
JOURNAL DE PHYSIQUE
Colloque C7, suppl6ment au n012, Tome 48, decembre 1987
LAWS OF CRYSTAL-FIELD DISORDERNESS OF ~ n IONS ~ +IN INSULATING LASER CRYSTALS
A . A . KAMINSKII
Institute of Crystallography, Academy of Sciences of the USSR, Leninsky Prospekt 59, 117333 Moscow, USSR
The main goal of present report, is to sum up our recent results of investigations of fundamental regularities, which stipulated crystal-f ield disorderness at Ln* ions in insulating laser crytals, using in the experiments on physics stimulated-emission (SE) spectroscopy.
The results of numerous investigations [l] shown, that crystal-fiels disorderness phenomena at ~n,+ -activator ions most hardly manifesting in crystals, having either statistics of structural elements or statistics of filling up similar crystallographic positions in lattice by cations with different valency. Such phenomenon results to the formation of variety of I.n3+
-
activator centers differ by crystal field, which strongly connected to each other by electron-excitation energy migration.Typical peculiarities of Ln3+ ions in crystals with disordered structure is their inhomogenously broaden bands in absorption and luminescence spectra and also usually more broaden SE lines at low temperature, than at T ) 300 K. In crystals with ordered structure the picture is opposite- all inter-Stark absorption (luminescence- transitions of ~ n = + ions have homogeneously broaden lines and hence, more narrow SE lines at low temperatures. (See Table and Figure)
Analysis and systematization of the results of study of disordered-laser- crystal structure and data of investigations of spectroscopic properties and SE indicate, that the nature of crystal-field disorderness at their Ln* activators is connected with two fundamental regularities. The first of them - structural dynamic disorderness is manifested in a variety of nonstoichiometric Mel-x%F,+x and R,-#e,F,, phases (where, M&a, Sr, Ba, Cd, Pb and R=Y, Sc, Ln). It is called dynamic, because the degree of structure disorderness will depend from the x value (from concentration of rare-earth and alkali-earth metals). Thus, in Mel-,~F,+x crystals under increasing x it takes place not simple introducing of charge-compensatinf F- anions, but change of one (or some) anions of origin structure into two (or more) F- anions to each R* cation moreover F- are dislocated not in the centers of the empty cubes of fluoEite (CaF,) structure, but statisticaly shifted by the direction to them to some distance. If speak about statisticaly probable ~ n * polyhedron in such crystals, then at x close to maximum, it will be ninevertex as distorded cube. With great probability one can say, that structural-dynamic disorderness determine spectroscopic and laser properties of ~ n * ions in a number of oxygen-containing laser crystals (solid solutions), forming in binary systems Me0 -R,O, (where Me-Hf,Zr and R-Y, Sc, Ln) and also in crystals YScO, with ~ d ions. ~ +
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987786
C7-360 JOURNAL DE PHYSIQUE
Another law of crystal-field disorderness at Ln3+ activators, called structural-static one, will be determine spectroscopic properties and character of SE-temperature behaviour of compounds, forming in ternary and more complicated physicochemical systems. In such crystals reconstruct ion of their polyhedra structure versus ~ n = + -ions concentration does not take place, because disorderness is seted into the origin of the structure and connected with statistical introducing (filling) of different-valency cations of the compounds into the similar crystallographic positions.
From the presented Figure and Table it follows, that independently from the type of laser-crystal disorderness, be it structural-dynamic or structural static one, always at low temperatures SE-excitation threshold of Nd3+ ions is higher than that is at 300 K. At the same excitation energy exceeding over threshold energy the SE linewidth of Nd* ions in such crystals is always higher at low temperatures. These temperature changes of SE parameters are stipulated by the electron- excitation-energy migration weakening with temperature decreasing over elementary ~ d = + -ions centers. The same temperature behaviour in SE parameters takes place in numerous laser neodymium glasses.
Thus, systematization and analysis o f accumulated knowledges on spectroscopic properties and SE of activated condensed media permited deeply understand fundamental objective laws of crystal-field disorderness phenomenon at Ln3+ (~d=+) ions in the insulating compounds and on their base solve some searching problem in the laser-crystal physics.
REFERENCES.
A.A. Kaminskii, L.K. Aminov et a1 Fizika i SpektrosJopia Lazernykh Kristallov, Nauka, Moskva 1986.
Table.
crystal T (K) SE wavelength SE threshold SE linewidth 3 10 3 15 9 6 10 12 15
Stimulated-emission spectroscopic parameters of ~ d * ions (laser channel 4F,,,
->
4111/2) in fluoride ans oxide crystals with structural-dynamic*) and structural-static**)C7-362 J O U R N A L DE PHYSIQUE
Stimulated-emission spectra (channel 4F,,,
->
411,,2) of ~ d = + ions in disordered oxide crystals and for comparision in Y,A1,O1, crystal with ordered structure and in phosphate glass. Standard Line with Ast-1.0561I.UII is indicated by an arrow.
