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Higher quantum efficiency due to an increase in oscillator strength give quantum dots the potential to rival traditionally used rare-earth ions as optically active centers for thermal sensing. The insensitivity of the emission to oxygen has established CdSe(ZnS) quantum dots as an attractive class of optical indicators for luminescence thermometry. A step towards developing useful low cost opto-sensing devices consists of immobilizing quantum dots in solid support structures.

In the present project, sol-gel method and spin coating technique are applied to produce thin films made of nanocomposite CdSe (ZnS) and CdS embedded in phosphor aluminosilicate matrix. The optical properties dependence on semiconductor nanoparticles size and, particularly the high temperature dependence of q-dot nanoparticle luminescence in a high temperature resistant matrix, are important in many thermometry applications.

In comparison with the other techniques, sol-gel method is more suitable to prepare optical materials as it permits molecular-level mixing and processing of the raw materials and precursors at relatively lower temperature and produces nano-structured bulk, powders and thin films.

The main concept of the project is based on investigating the luminescence properties of thin films based on CdSe and CdS semiconductor quantum dots passivated with a large bandgap semiconductor (ZnS) embedded in an inorganic matrix to be used as temperature sensing materials. Optically transparent matrices containing quantum dots are desired for opto-sensing applications.The project proposal intends to extend the recent research related on nanocomposites composed of CdSe (ZnS) nanosized particles set in a SiO₂ matrix whose high temperature luminescence-based sensing is a promising topics to be investigated. The novelty of the project consists in investigations that aim at determining the influence of the matrix nature (SiO₂, SiO₂-P₂O₅, SiO₂-P₂O₅-Al₂O₃) and the CdS and/or CdSe embedded quantum dots on the luminescent properties of the complex nanocomposite material that will be used as temperature sensor.

The novelty of the project proposal can be summarized as follows:

• Two novel matrixes P₂O₅-SiO₂ and P₂O₅-Al₂O₃-SiO₂ to embed CdS(ZnS)/CdSe(ZnS) quantum dots will be prepared, aiming at investigating the influence of the matrix on the fluorescence properties of the nanocomposite material;

• Two different novel approaches to prepare thin films of CdS(ZnS)/CdSe(ZnS) embedded in phosphor aluminosilicate matrix will be used, both based on sol gel technique: (i) semiconductor nanoparticles previously synthesized immersed in the appropriate sol-gel mixture and (ii) semiconductor nanoparticles' precursors and the matrix precursors mixed together to form the sol-gel;

• New nanocomposites consisting of CdS (ZnS)and CdSe(ZnS) quantum dots embedded in phosphor silicate and phosphor aluminosilicate thin films will be synthesized and structural/ optical characterized.

1. Highlight the properties changes resulting from the quantum confinement effect of CdS/CdSe embeded in thin films of phosphor aluminosilicate matrix;

2. Evaluation of the increased surface-to-volume ratio of the CdS/CdSe quantum dots on the properties of nanocomposite thin films based on phosphor aluminosilicate matrix;

3. Establishment of the mechanisms that govern the properties of CdS/CdSe quantum dots embeded in thin films due to the phosphor aluminosilicate matrix composition;

4. Assesment of sol gel method to synthesize thin films of CdS/CdSe embeded in phosphor aluminosilicate matrix as a promising new temperature sensing material.

The tasks: (i) synthesis of thin films nanocomposites CdSe (ZnS) embedded in phosphor aluminosilicate matrix; (ii) synthesis of thin films nanocomposites CdS (ZnS) embedded in phosphor aluminosilicate matrix; (iii) investigation of the photoluminescence dependency on the change of SiO₂, P₂O₅ and Al₂O₃ matrix composition; (iv) exploration of the luminescence features on the type of silica, phosphorous pentoxide and alumina precursors; (v) study of emission peak wavelength, full width at half maximum, emission intensity and energy bandgap dependence with respect to temperature; (vi) investigation of bandgap change upon thin films thickness modification; (vii) analysis of the nanocomposite stability (wavelength shift) under thermal cycling (cool down and temperature raising); (viii) optical and structural characterization (UV-Vis-NIR, photoluminescence, FourierTransform Infrared-FTIR and Raman spectroscopy, XRD analysis, THz spectroscopy) of the nanocomposites in correlation with their tunable size; (ix) study of the thin films microstructure by atomic force microscopy (AFM), transmission and scanning electron microscopy (TEM and SEM); (x) study the temperature dependence of photoluminescence emission using an appropriate experimental set up.

The research team is composed of one project coordinator with relevant national and international scientific activity (PI-chemical engineer) Dr. Mihail Elisa; 1-physicist, Dr. Cristiana Eugenia Ana Grigorescu, 1 organic chemical engineer, Dr. Ileana Cristina Vasiliu and 1 electronic engineer, Dr. Irinela Chilibon, two PhDs physicist students, Drd. Raluca Iordanescu and Drd. Ionut Feraru and two technicians: chemist, Ionica Manea and electronician, Sorin Manea.