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Study of Perovskite Quantum Dots for Super-resolution Microscopy Applications
Publication . Meixeiro, Ana Carolina Espada Antunes e Natal; Laia, César; Pereira, Luís
Quantum Dots (QDs) are known for their remarkable optical properties, such as, high
photoluminescent quantum yields (PLQY), large absorption spectra, narrow emission
spectra, excellent photostability and the possibility to shift the fluorescence emission in a
wide spectrum of colours through QD synthesis conditions [1–4]. When compared with
conventional fluorophores, QDs show many advantages, like resistance to photobleaching,
enhanced photostability and brightness [5]. In this work Iodine Perovskite Quantum Dots
(CsP bI3) were used, since this type of QDs show great photophysical properties and nearinfrared
(NIR) emission. Nevertheless, their structural stability and shelf life needed
improvement, so a doping system based on cadmium was developed, and alterations
in the synthesis were studied to fulfil the needs without causing any kind of drawback.
An extensive optical, chemical and morphological characterisation was carried out to
fully understand the influence of the developed particle engineering. It was proven that
the doping system and synthesis modifications increase the stability of the nanocrystal,
without pitfalls. Finally, different Super Resolution Microscopy techniques were used
to investigate the performance of the PQDs, the possibility of using them as fluorescent
dyes and a possible resolution enhancement.
Zeólitos sodalite emissivos para aplicação em iluminação
Publication . Viola, Catarina Sofia Miranda; Ruivo, Andreia; Laia, César
Atualmente, a população está cada vez mais dependente da iluminação, usando-a intensamente no seu quotidiano. O desenvolvimento de LEDs revolucionou este campo, devido às suas altas eficiências energéticas e baixos consumos. Na produção de LEDs normalmente são utilizados phosphors, que têm na sua composição mariotariamente terras-raras, cuja utilização se prevê muito limitada a curto prazo, tornando-se essencial o estudo de outros materiais para utilizar como phosphors. As alternativas podem passar pelo uso de zeólitos luminescentes, que apresentam rendimentos quânticos na ordem dos 97%. Os zeólitos sodalite também demonstram propriedades interessantes, tais como rendimentos quânticos de 53%, desvios de Stokes de 250 nm e estabilidade térmica até aos 450 ºC.
A hackmanite é um mineral de sodalite natural com enxofre na sua composição e uma fórmula química de Na8[SiAlO4]6(Cl,S)2, podendo ser sintetizada em laboratório através de uma síntese em estado sólido, partindo do zeólito LTA.
Com o objetivo de alargar a aplicabilidade destes zeólitos sodalite, foram feitas várias sínteses em atmosfera redutora com diferentes concentrações de enxofre e diferentes halogéneos, alterou-se também o calcogénio e, por fim, foram introduzidos metais na sua estrutura.
As espécies fotoluminescentes S2- e Se2- foram encontradas nestas sodalites com desvios de Stokes de cerca de 250 nm, máximos de intensidade de emissão aos 650 nm e 740 nm e rendimentos quânticos de 46% e 48%, respetivamente. Com a introdução da prata na estrutura da sodalite, obtiveram-se compostos com luminescência branca. Também se introduziu chumbo, obtendo-se um desvio do espetro de emissão com um máximo de intensidade aos 610 e aos 680 nm, respetivamente para as espécies S2- e Se2-.
Estes zeólitos sodalite mostraram ser bastante promissores na substituição dos phosphors de LEDs comerciais devido às suas propriedades óticas. Os zeólitos resultantes da interação com o chumbo podem ainda ser utilizados em concentradores solares luminescentes.
Photoluminescent properties of doped alkali borosilicate glasses
Publication . Almeida, Mário André Madeira de; Ruivo, Andreia; Àguas, Hugo
This project was developed with the purpose to achieve innovative solutions of UV light down conversion. Such was accomplished through the synthesis of photoluminescent glasses doped with tin oxide and copper oxide, also preliminary studies on the development of photoluminescent thin films based on the same elements was approached. Photoluminescent quantum yields and Stokes shift were taken as guidelines to evaluate the photoluminescent behaviour of the produced samples.
The synthetic strategy applied for photoluminescent glass samples was systematic, it consisted on the insertion of a variable doping amount of each element over an alumina-borosilicate glass matrix which were prepared at high temperatures of 1400 ºC and 1550 ºC. Structural features were evaluated through SSNMR for 29Si, 11B, 23Na, and Raman spectroscopy, which showed that doping does not affect the network structural matrix. Dilatometry measurements were performed showing a negligible variation of the thermomechanical properties of the samples.
Doping concentrations have revealed to be a key factor for the achievement of high quantum performances, where we have observed triplet state light emission derived from three emissive species. Its origin resides in Sn2+, Sn2+ aggregates and Cu+ species in the glass matrix. Tin oxide doped samples shown quantum efficiencies of 50% and 1.7 eV Stokes shift for 1.4% molar tin oxide concentration, while copper oxide doped samples present 58% quantum efficiency and large 3 eV Stokes shift for 0.14% molar concentration.
Thin film deposition strategy was based on the identification of optimal conditions for the formation of copper and tin oxide crystalline phases. Results were evaluated through X-ray diffraction and Raman spectroscopy showing the formation of both crystalline phases over variable oxygen flow. A multi-layer thin film deposition was performed and diffusion was attempted through thermal treatment. Results indicate the formation of a protective SnO2 layer over the formation of Cu2O phase, increasing its thermal stability to 400 ºC.
Synthesis of Inorganic Halide Perovskite Quantum Dots for Photoluminescence Applications
Publication . Magalhães, Débora Vale; Laia, César; Mendes, Manuel
Metal halide perovskite crystal structures have emerged as an attractive class of optoelectronic materials due to their excellent optical absorption and emission properties. Restricting the physi-cal dimension of the crystallite to the nanometer scale revealed quantum-confinement effects sim-ilar to those presented by traditional chalcogenide quantum dots. The synthetized inorganic per-ovskite quantum dots (IPQD) were characterized by spectroscopic measurements (absorption and photoluminescence emission spectra). Two synthesis methods were studied (supersaturation re-crystallization (SR) and hot-injection method (HI)) and the latter was chosen to be employed for the remaining work stages, due to observed better properties. The final goal was to obtain IPQDs doped with metals, focusing in Cd2+. The obtained samples of bromide-based perovskite doped with CdI2 exhibit more defined emission peaks with smaller full width at medium height (FWHM) and the samples appear to show improved stability when compared with blank CsPbBr3. The smaller FWHM was also observed for the CsPbI3 doped with CdI2. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was performed for samples with 10 mol% and 30 mol% of CdI2, where it was verified that 2.6 % and 8.23 % of the doping was introduced in the final compound, respectively. Note that the latter value was significantly better than those reported in literature (about 2% of the initial amount). The observed optical properties and empirically im-proved stability make these nanocrystals promising materials in several optoelectronic applica-tions, namely LEDs, solar cells, lasers, among others.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/QEQ-QIN/3007/2014