Intensificação da luminescência de complexo de Eu(III) por plasmon de superfície em filmes de Langmuir e Langmuir-Blodgett
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Data
2021-04-09
Autores
Assis, Douglas Ricardo de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Avanços na área de materiais luminescentes, apontam na direção da conformação destes materiais em sistemas bidimensionais, visando a otimização das propriedades ópticas para diversas aplicações. Dentre as técnicas de preparação de filmes finos, a técnica de Langmuir-Blodgett (LB) é a mais promissora para o controle da espessura e a organização em nível molecular dos filmes. A associação de nanopartículas plasmônicas com a conformação bidimensional dos luminóforos é uma estratégia potencial para a intensificação da luminescência. Este trabalho tem como objetivo otimizar os parâmetros relacionados às medidas de espectroscopia de fotoluminescência com excitação ultravioleta in situ na cuba de Langmuir-Blodgett (UV-PLS in situ), relacionar as propriedades luminescentes com a organização molecular 2D dos filmes e investigar os efeitos de nanopartículas de prata nas propriedades fotoluminescentes quando presentes em filmes de Langmuir e LB do complexo [Eu(tta)3(phen)]. Medidas de UV-PLS in situ, em tempo real foram realizadas durante a preparação dos filmes de Langmuir e LB, na qual foram observadas mudanças significativas na intensidade da luminescência quando ocorre as transições de fases indicando que o Eu3+ é uma sensor espectroscópico da organização do filme. Foram obtidas pelo método poliol nanopartículas Ag@AO-OL com diâmetro médio ~10 nm, recobertas com ácido oleico (AO) e oleilamina. A isoterma e a curva do módulo de compressão superficial sugere um empacotamento gradual das nanopartículas conforme o filme é comprimido. A isoterma do [Eu(tta)3(phen)] puro mostrou baixo grau de empacotamento das moléculas do complexo, não apresentando colapso do filme e indicando uma dificuldade na formação do filme de Langmuir. Desta forma, foram preparados filmes mistos [Eu(tta)3(phen)]:AO variando % em mol de ácido oleico e o filme com 10,0% em mol AO se apresentou mais estável. Filmes mistos [Eu(tta)3(phen)]:Ag variando % em massa de Ag@AO-OL foram preparados e o filme que apresentou maior intensidade de emissão foi o filme com 10,0% em massa de Ag@AO-OL. A partir do filme misto [Eu(tta)3phen]:AO_10,0% foi investigado o efeito na luminescência provocado pela adição de % em massa de Ag@AO-OL e foi observado que existe uma faixa de concentração ideal de Ag@AO-OL (8,3 a 13,3%), no qual o erro das medidas é menor indicando a formação de filmes estáveis. O filme LB misto [Eu(tta)3phen]:AO:Ag_10,0% do tipo Z apresentou os maiores fatores de intensificação e a maior eficiência quântica. Comparando os valores de CR dos filmes nos dois mecanismos de excitação dos quatro tipos de filmes LB preparados observa-se maior intensificação da luminescência quando a excitação é feita em 322 nm (excitação no ligante). Conclui-se que o plasmon de superfície das nanopartículas intensifica o campo eletromagnético da radiação excitante, intensificando a absorção do ligante antena que transfere a energia para o Eu3+. A transição 5D0 → 7D2 sofre uma maior intensificação, indicando que a presença da prata influencia mais as transições permitidas pelo mecanismo por dipolo elétrico. Os filmes LB apresentam o mesmo comportamento dos filmes de Langmuir e a intensidade de emissão de uma monocamada depositada em substrato de quartzo, evidencia a potencial aplicação destes filmes em dispositivos ópticos.
Advances in luminescent materials area, point in the direction of the conformation of these materials in two-dimensional systems, to optimize of optical properties for several applications. There are several techniques to prepared thin films, but the Langmuir-Blodgett (LB) technique is the most promising, as they provide good control over the thickness and homogeneity of the monolayers. The association of plasmonic nanoparticles with the two-dimensional conformation of the luminophores is a potential strategy for the luminescence enhancement. This work has as objective to optimize in situ photoluminescence spectroscopy (UV-PLS in situ) at Langmuir-Blodgett trough parameters, correlate the luminescent properties to 2D molecular organization of the films and investigate the silver nanoparticles effects in luminescent properties when incorporated into [Eu(tta)3(phen)] Langmuir and LB films. Real-time UV-PLS in situ measurements were performed during the preparation of the Langmuir and LB films, in which significant changes in luminescence intensity were observed when phase transitions occur, indicating that Eu3+ is a spectroscopic probe of the organization film. Ag@AO-OL nanoparticle synthesize by polyol method were obtained with an average diameter of ~ 10 nm, covered with oleic acid (AO) and oleylamine. The isotherm and the surface compressional modulus suggest a gradual packing of Ag@AO-OL as the film is compressed. The isotherm of pure [Eu(tta)3(phen)] showed a low degree of packaging without film collapse, indicating a difficulty in Langmuir film organization. In this way, [Eu(tta)3(phen)]:AO mixed films were prepared using different mol % of oleic acid and the film with 10.0% mol AO were more stable. [Eu(tta)3(phen)]:Ag mixed films using different mass % of Ag@AO-OL were prepared and the film with the highest emission intensity was the film with 10.0% Ag@AO-OL. From the [Eu(tta)3phen]:AO_10.0% mixed film, the effect on luminescence caused by the addition of % mass of Ag@AO-OL was investigated, and it was observed that there is an ideal concentration range of Ag@AO-OL (8.3 to 13.3%), in which the measurement error is lower, indicating the formation of stable films. [Eu(tta)3phen]:AO:Ag_10.0% mixed LB film of type Z presented the greatest intensification factors and the highest quantum efficiency. Comparing the CR values of the films in the two excitation mechanisms of the four types of prepared LB films, a greater luminescence enhancement is observed when the excitation is done at 322 nm (excitation in the ligand). It is concluded that the nanoparticles surface plasmon enhanced the electromagnetic field of the exciting radiation, intensifying the absorption of the antenna ligand that transfers the energy to Eu3+. The transition 5D0 → 7D2 undergoes a greater enhancement, indicating that Ag@AO-OL presence influences more the transitions allowed by the electric dipole mechanism. LB films exhibit the same behavior as Langmuir films and the emission intensity of one monolayer deposited on a quartz substrate, demonstrates the potential application of these films in optical devices.
Advances in luminescent materials area, point in the direction of the conformation of these materials in two-dimensional systems, to optimize of optical properties for several applications. There are several techniques to prepared thin films, but the Langmuir-Blodgett (LB) technique is the most promising, as they provide good control over the thickness and homogeneity of the monolayers. The association of plasmonic nanoparticles with the two-dimensional conformation of the luminophores is a potential strategy for the luminescence enhancement. This work has as objective to optimize in situ photoluminescence spectroscopy (UV-PLS in situ) at Langmuir-Blodgett trough parameters, correlate the luminescent properties to 2D molecular organization of the films and investigate the silver nanoparticles effects in luminescent properties when incorporated into [Eu(tta)3(phen)] Langmuir and LB films. Real-time UV-PLS in situ measurements were performed during the preparation of the Langmuir and LB films, in which significant changes in luminescence intensity were observed when phase transitions occur, indicating that Eu3+ is a spectroscopic probe of the organization film. Ag@AO-OL nanoparticle synthesize by polyol method were obtained with an average diameter of ~ 10 nm, covered with oleic acid (AO) and oleylamine. The isotherm and the surface compressional modulus suggest a gradual packing of Ag@AO-OL as the film is compressed. The isotherm of pure [Eu(tta)3(phen)] showed a low degree of packaging without film collapse, indicating a difficulty in Langmuir film organization. In this way, [Eu(tta)3(phen)]:AO mixed films were prepared using different mol % of oleic acid and the film with 10.0% mol AO were more stable. [Eu(tta)3(phen)]:Ag mixed films using different mass % of Ag@AO-OL were prepared and the film with the highest emission intensity was the film with 10.0% Ag@AO-OL. From the [Eu(tta)3phen]:AO_10.0% mixed film, the effect on luminescence caused by the addition of % mass of Ag@AO-OL was investigated, and it was observed that there is an ideal concentration range of Ag@AO-OL (8.3 to 13.3%), in which the measurement error is lower, indicating the formation of stable films. [Eu(tta)3phen]:AO:Ag_10.0% mixed LB film of type Z presented the greatest intensification factors and the highest quantum efficiency. Comparing the CR values of the films in the two excitation mechanisms of the four types of prepared LB films, a greater luminescence enhancement is observed when the excitation is done at 322 nm (excitation in the ligand). It is concluded that the nanoparticles surface plasmon enhanced the electromagnetic field of the exciting radiation, intensifying the absorption of the antenna ligand that transfers the energy to Eu3+. The transition 5D0 → 7D2 undergoes a greater enhancement, indicating that Ag@AO-OL presence influences more the transitions allowed by the electric dipole mechanism. LB films exhibit the same behavior as Langmuir films and the emission intensity of one monolayer deposited on a quartz substrate, demonstrates the potential application of these films in optical devices.
Descrição
Palavras-chave
Filmes de Langmuir, Filmes de Langmuir-Blodgett, Luminescência in situ, Langmuir films, Langmuir-Blodgett films, Luminescence in situ, Plasmon de superfície, Nanopartículas de prata, Intensificação da luminescência, Surface plasmon, Silver nanoparticles, Luminescence enhancement