Synthesis and characterization of luminescent thin films for optical thermometry and investigation of gold nanostructures

Abstract

Luminescent phosphors based on lanthanide ions have shown excellent performance in temperature measurements as ratiomeric thermometers. The advantages of this system are the high thermal sensitivity, the relative short acquisition time, the spatial resolution (>10um) and high quantum yields. Recently, thermometric nanosystems based on bismuth oxides doped with lanthanides were investigated. Bi2SiO5 has been used with host for upconverting systems showing good stability properties. The main aim of this experimental work is the synthesis and characterization of a luminescent Bi2SiO5 crystalline film doped with lanthanide ions to be used as an optical thermometer. Different techniques have been tested to obtain a homogeneous luminescent thin film. The strategy that has shown the best results in terms of reproducibility and final optical properties is a sol-gel deposition by spin coating employing bismuth and lanthanides nitrates and TEOS as source of silicon. Two systems have been investigated: i. Bi2SiO5-Nd3+(2%) and ii. Upconversion Bi2SiO5-Er3+(1%)Yb3+(10%). Structural and morphological characterization of the materials was performed by FT-IR, DSC/TGA, XRPD, SEM/EDS analysis. The study of the optical properties and the calibration of the thermometers were obtained by means of room temperature and temperature dependent photoluminescence analysis and described through the Boltzmann law. In addition, the combination of the optical thermometer with plasmonic-induced heating of gold nanoparticles was investigated. The synthesis of gold nanoparticles and nanorods of different sizes was also carried out. The gold particles were characterized by SEM, analytical centrifuge and UV-VIS spectroscopy. Finally, the interaction between the metal nanoparticles and the luminescent film was preliminarily explored by means of optical analysis. The results obtained are encouraging and pave the way for a new type of optical ratiomeric thermometers.