on the occasion of his 75th birthdayThe optical spectra of tin-doped NaCl crystals are investigated. Special attention is paid to the effects of concentration and thermal history of the crystals. Within aggregates the SnZ+ cation exhibits characteristic absorption and emission bands. The experimental data show that the tin ions present a double band emission specific for each of the dispersion states of the impurity in the crystal.On prksente les spectres optiques obtenus pour les cristaux de NaCl dop6s a11 Sn, en poursuivant spkcialement les effcts de concentration et du traitement thermique. Lc cation Sn2+ appartenant aux agrkgats montre des bandes d'absorption e t d'kmission charactkristiques. Les rksultats expkrimentaux indiquent clue les ions de Sn prksentent deux bandes d'6mission spkcifiques pour chaquo ktat de dispersion de l'impuretk dans Ie cristal.
The emission spectra of KCl :Pb and KBr:Pb are measured as a function of the impurity concentration in the crystals. The low energy emission depends stronger on the impurity concentration in crystals than the principal emission andisless excited within the A absorption band than within the C band. The low energy emission is well explained by the existence of a resonant transfer between -v IlP,) + , u I3P1) and p IlP,) + v I3P1) electronic states.Les spectres d'kmission de KC1:Pb et KBr:Pb ont 6th mesur6s en fonction de la concentration des impuretBs dans les crist6aux. L'Bmission de basse 6nergie depend plus fortement que 1'6mission principale de la concentration des impuret6s dans le cristal, et d'autre part, le randament quantique de l'excitation dans la bande C est plus grand que celui de la bande A #absorption. L'Bmission de basse 6nergie est expliquBe par un transfert resonant d'hergie entre lea Btats 6lectroniques -v IlP,) + p lap,) et p llPl> + v ISP,).
Some experimental results concerning the decay times of the luminescence emission of Pbe+ centres in KCl and NaCl crystals are reported and discussed in order to clarify the origin of the two emissions excitable in the A absorption band. The experimental features support the luminescent Pbe+ centre model implying a resonant energy transfer.Des r6sultats experimentaux concernant l'extinction des 6missions luminescentes des centres Pb2+ en cristaux de NaCl et KCl sont pr6sentks et discutes dans le but de clarifier l'origine des deux 6missions produites par irradiation dans la bande A d'absorption. Les donnks exp6rimentales sont en bien accord avec le modhle de centre luminescent impliquant un transfert r6sonan. d'6nergie.
Investigations of the optical spectra proper to ns ions in alkali halides were the object of an intense-research. Nevertheless there are very few data on the optical properties of lead doped N a B r 11, 2/ due perhaps to the hygroscopic character of this crystal.The purpose of this note is to present some new data about the optical spectra, influence of the hydrolysis products, of the lead concentration, and of the dispersion state of the impurities.Single crystals of NaBr:Pb were grown by the Bridgman method from a material dried in vacuum, with an impurity concentration of (C,) and (C,) molar fraction. Due to the hygroscopic character of sodium bromide, our single crystals were carefully manipulated to avoid adsorption and inclusion of water.The samples were submitted to different treatments a s follows: type I, the sample was heated at 900 K for several hours and quenched down quickly at room temperature (RT); type 11, the sample was slowly cooled aftergrowth and stored at RT for several months before the measurements; type 111, the sample was heated in air saturated with water at 350 K.The absorption and emission spectra were recorded at liquid nitrogen temperature (LNT) . In the type 111 sample the cationic Pb2' impurities and OH anions yield complexes which present an absorption band at about 270 nm. Excitation in this range at LNT produces a specific luminescence peak at 358 nm, the excitation peak being at 269 nm (Fig. lb). The absorption and emission bands proper to Pb2+-OH-complexes, a r e independent of the thermal treatment of the samples, explaining in this way the great stability of such complexes.
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