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Doctoral Thesis
DOI
Document
Author
Full name
Antonio Carlos de Castro
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1999
Supervisor
Committee
Li, Maximo Siu (President)
Blak, Ana Regina
Ribeiro, Sidney José Lima
Rodrigues Filho, Ubirajara Pereira
Zilio, Sérgio Carlos
Title in Portuguese
Espectroscopia óptica de aglomerados Yb2+/CN- em haletos de potássio
Keywords in Portuguese
Espectroscopia óptica
Haletos de potássio
Íon cianeto
Itérbio
Abstract in Portuguese
Estudamos as propriedades de absorção e emissão de aglomerados Yb2+/CN- em haletos de potássio (KCl, KBr e KI) e estamos propondo um modelo para a estrutura geométrica do aglomerado. Neste modelo o itérbio divalente e o íon cianeto substituem um cátion e um ânion vizinhos, respectivamente, com o eixo que une os dois íons na direção <100>. O acoplamento entre os dois impede o movimento rotacional do cianeto, mesmo à temperatura ambiente, como pode ser comprovado pela presença de linhas estreitas no espectro de absorção infravermelha. Os espectros de absorção visível e ultravioleta são compatíveis com as transições 4ƒ14→ 4ƒ13 5d do itérbio em simetria C4v. A absorção vibracional indica a presença não intencional de OCN- que pode formar aglomerados com os íons cianeto. À temperatura do nitrogênio líquido, observa-se a influência do itérbio sobre os estados rotacionais do cianeto, uma indicação da interação entre centros vizinhos. A excitação sobre as bandas de absorção ultravioleta e visível produz intensa emissão em que podem ser identificadas três regiões (450→500 nm, 500→600 nm e acima de 600 nm) com comportamentos distintos quanto à variação da temperatura e excitação. Os tempos de vida variam de 50µs à temperatura ambiente até 20 ms à temperatura do hélio líquido. Simultaneamente à emissão visível, observa-se a emissão vibracional-rotacional dos íons cianeto, com indicações de transferência de energia entre os íons cianeto acoplados ao itérbio e os isolados
Title in English
Optical spectroscopy of Yb/CN- in potassium halides
Keywords in English
Cyanide ion
Itterbium
Optical spectroscopy
Potassium halides
Abstract in English
We have studied the absorption and emission properties of the Yb2+/CN- in potassium halides (KCl, KBr and KI) and it was proposed a structural model for this system. In this model the divalent ytterbium and the cyanide ion substitute a neighboured cation and an anion along a <100> direction. The rotational motion of the cyanide ion is constrained by the coupling with the ytterbium, which is by the presence of narrow lines in the infrared absorption spectra, even at room temperature. The UV and visible absorption spectra are compatibles with the 4ƒ14→ 4ƒ13 5d ytterbium transitions under C4v symmetry. The vibrational absorption reveals the unintentional presence of OCN- that can form clusters with cyanide ions. The influence of the ytterbium over the rotational states of cyanide can be observed at liquid nitrogen temperature, revealing the interaction between both impurities. The optical excitation if the absorption bands shows a broad and strong emission in three regions (450→500 nm, 500→600 nm and above 600 nm) with different behaviors under temperature and excitation pump changes. Lifetimes between µs at room temperature and 20 ms at liquid heliurn temperature can be observed. Simultaneously to the visible emission, it was observed the vibrational-rotational emission of CN- ions with evidences of energy transfer between coupled Yb/CN- pairs and isolated CN- ions
 
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Publishing Date
2014-11-26
 
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