In this work, we have investigated the thermal properties (diffusivity (D), conductivity (K), temperature coefficient of the optical path length change (ds/dT), etc) and loss processes owing to the ion-ion interactions, in Nd3+ doped laser materials, specifically YAG ceramic and CGGG crystal. Since the fluorescence quantum efficiency, , is directly related to these mechanisms that lead to luminescence quenching, the studies were carried out mainly observing the effects of these processes on . To this goal we used mainly the thermal lens technique and conventional spectroscopy. In Nd:YAG ceramic, we have investigated the losses due to down-conversion or, as they are well known, concentration quenching that are basically cross relaxation (CR) and energy migration (EM). From these results, it was concluded that the main source of luminescence quenching is CR and that the small ds/dT value together with the high optimum concentration put this material as candidate for several applications. In Nd:CGGG crystal, we have studied the loss processes owing to upconversion or, as is better known, upconversion Auger (UA) or energy transfer upconversion, which are important in laser systems of high. / Fundação de Amparo a Pesquisa do Estado de Alagoas / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho investigamos as propriedades térmicas (difusividade (D), condutividade (K), variação do caminho óptico com a temperatura (ds/dT), etc) e processos de perdas devido a interações entre íons, em materiais lasers dopados com Nd3+, especificamente cerâmica de YAG e cristal CGGG. Desde que a eficiência quântica de fluorescência, , está diretamente relacionada com esses mecanismos que levam a supressão da luminescência, os estudos foram realizados principalmente observando os efeitos desses agentes sobre . Para esse propósito, usamos principalmente a técnica de lente térmica e espectroscopia convencional. Na cerâmica de Nd:YAG investigamos as perdas por down-conversion ou, como é melhor conhecidas, quenching de concentração que são basicamente relaxação cruzada (RC) e migração de energia (ME). Nesses resultados concluímos que a principal fonte de supressão da luminescência é RC e que o valor de ds/dT baixo juntamente com a concentração ótima alta apresentam esse material com boas perspectivas de aplicações. No cristal Nd:CGGG estudamos os processos de perdas por upconversion ou, como é melhor conhecido, conversão ascendente Auger (CAA) ou conversão ascendente por transferência de energia, os quais são importantes em sistemas lasers de alta potência e/ou altas concentrações de íons dopantes. Com a presença dos processos de CAA é adicionado mais um canal de decaimento não radiativo. E como resultado foi observado uma diminuição de η e consequentemente um aumento da carga térmica (φ). O conhecimento dos processos investigados nesta dissertação é de importância fundamental para a engenharia e caracterização de matérias lasers.

Text in Afrikaans with Abstracts in Afrikaans, English and isiZulu / In hierdie proefskrif word ondersoek ingestel na die parateks as narratiewe strategie vir toeganklikheid in geselekteerde Afrikaanse kinder- en jeugliteratuur. Die kern van hierdie ondersoek is die toeganklikheid van die boodskap binne die paratekstuele en narratiewe kommunikasiesituasie. Vir hierdie ondersoek is die sentrale probleemstelling soos volg geformuleer: hoe word die parateks as narratiewe strategie gebruik om kinder- en jeugliteratuur meer toeganklik vir jong lesers te maak? Gérard Genette se werk oor die parateks (1997a) en die narratologie (1983, 1990) dien as teoretiese basis vir hierdie studie se konseptuele raamwerk, aangevul deur die werk van Mieke Bal (1991, 2009). Jauss (1982) se resepsie-estetika word ook betrek ten einde toeganklikheid ten opsigte van die primêre teikenmark te formuleer. Binne die konteks van hierdie konseptuele raamwerk, word daar afsonderlik ondersoek ingestel na die ontvangers, senders en boodskap van die paratekstuele en narratiewe kommunikasiesituasie. Die ontvangers is die lesers van die parateks as narratiewe strategie vir toeganklikheid en word bespreek as die primêre, dubbele en tweeledige teikenmarkte. Die senders is die verskillende skrywers betrokke by die skepping en implementering van die parateks as narratiewe strategie vir toeganklikheid. Onderskeid word getref tussen die primêre skrywer, die tweede skrywer en die sekondêre skrywer. Laastens word die boodskap ondersoek soos dit met die visuele parateks en die talige parateks verband hou. Aan die hand van die konseptuele raamwerk van hierdie studie, en die verskillende rolspelers en boodskappe binne die paratekstuele en narratiewe kommunikasiesituasie, dui die studie aan hoe die parateks as narratiewe strategie gebruik kan word om kinder- en jeugliteratuur vir veral die primêre teikenmark meer toeganklik te maak. / This thesis sets out to illustrate how the paratext can be used as narrative strategy for accessibility in selected Afrikaans children’s and youth fiction. Central to this study is the accessibility of the message in the paratextual and narrative communication situation. In this regard, the central research question is as follows: how can the paratext be used as a narrative strategy to make children’s and youth literature more accessible for young readers? Gérard Genette’s work on the paratext (1997a) and narratology (1983, 1990) serves as the theoretical basis for this study’s conceptual framework, along with the work of Mieke Bal (1991, 2009). In order to define accessibility in terms of the primary target audience, reference is also made to Jauss’s (1982) reception theory. Within the context of this conceptual framework, focus is placed on the receivers, senders and message of the paratextual and narrative communication situation. The receivers are the readers of the paratext as narrative strategy for accessibility and are discussed as the primary, twofold and dual target audiences. The senders are the different writers involved in the creation and implementation of the paratext as narrative strategy for accessibility. Here a distinction is made between the primary writer, the second writer and the secondary writer. Lastly, the message is discussed as it relates to the visual paratext and textual paratext. Through the conceptual framework of this study, along with the different role players and messages of the paratext as narrative strategy for accessibility, this study shows how the paratext as narrative strategy can be used to make children’s and youth literature more accessible for especially the primary target audience. / Le thisisi ihlose ukuveza ukuthi umbhalo ohunyushiwe ungasetshenziswa kanjani njengesu lokuxoxa emibhalweni ekhethiwe yesiBhunu yezingane kanye naleyo yabantu abasha .Okubalulekile kulesi sifundo socwaningo wukutholakala komlayezo wombhalo ohunyushiwe kanye nesimo sokuxhumana ngengxoxo. Ngalokho-ke, umbuzo oyinsika kulesi sifundo socwaningo ngolandelayo: Ngabe inkulumo ehunyushiwe ingasetshenziswa kanjani njengesu lokuxoxa, elingenza ukuthi imibhalo yobuciko yezingane kanye naleyo yabantu abasha ukuze itholakale kalula kubafundi abasebasha? Umsebenzi kaGérard Genette i-paratext (1997a) kanye ne-narratology (1983, 1990) usebenza njengesisekelo sesakhiwo sebizo salesi sifundo socwaningo, kanti lokhu kuhambisana nomsebenzi ka MiekeBal (1991,2009). Ukuze siphumelele ukuchaza mayelana nokutholakala kwabafundi bezincwadi abahlosiwe, uyanxuswa ukuthi ufunde ithiyori emayelana nokutholakala kwabafundi bomlayezo ka Jauss (1982). Ngaphansi kwesimo sesakhiwo segama, kugxilwe kakhulu kubamukeli, kubathumeli kanye nakumlayezo wombhalo ohunyushiwe kanye nesimo sokuxhumana ngengxoxo. Abamukeli bomlayezo kungabafundi bombhalo ohunyushiwe, okuyisu elisetshenziswa ukuthola umlayezo, kanti la masu axoxwa njengalawo aqonde abafundi bokuqala, abambaxambili futhi anezinhloso ezimbili.. Abathumeli bomlayezo kungabhali abadlala indima yokwakha kanye nokusebenzisa imibhalo ehunyushiwe njengesu lokuxoxa elisetshenziswa ukuthola umlayezo. Lapha, kuvezwa umehluko ophakathi kombhali wokuqala, umbhali wesibili kanye nombhali osezingeni lesibili. Okukugcina, umlayezo uxoxwa njengoba uhlobana nombhalo ohunyushiwe obukelwayo kanye nombhalo ohunyushiwe olotshiwe Ngokusebenzisa uhlelo lwesakhiwo segama salesi sifundo, esisebenzisana ndawonye nabadlali bendima abahlukahlukene kanye nemilayezo yombhalo ohunyushiwe njengesu lokuxoxa elisetshenziswa ukuthola umlayezo, lokhu kukhombisa ukuthi umbhalo ohunyushiwe oyisu lokuxoxa ungasetshenziswa kanjani ukwenza ukuthi imibhalo yobuciko yezingane kanye naleyo yabantu abasha ingatholakala kanjani, ikakhulukazi ngabafundi bokuqala abahlosiwe. / Afrikaans and Theory of Literature / D. Litt et Phil. (Afrikaans)