Novel Inorganic–Organic Luminescent Materials by Atomic/Molecular Layer Deposition

Abstract

Luminescent hybrid inorganic-organic materials form an exciting material family used for light generation, conversion, and amplification. Chromophores coupled to lanthanides in such type of materials are responsible for the efficient energy transfer to the emitting lanthanide ions. Integration of the inorganic and organic components in the atomic/molecular scale results in hybrid nanostructures enabling new luminescent, electronic and optoelectronic properties. The controlled deposition of these materials on complex surface architectures is a yet unresolved issue, which is essential for the next-generation luminescent nanodevices, such as medical detection devices, photovoltaic solar panels, and light-emitting diodes. However, quite a few synthetic techniques of this kind exist. To address this gap, novel atomic/molecular deposition (ALD/MLD) processes have been developed in recent years. The strongly emerging ALD/MLD technique has the advantage of linking the inorganic and organic layers into hybrid nano-networks with their thicknesses and compositions controlled within atomic/molecular level precision. It is the only available gas-phase deposition technique to produce such hybrid materials. In this thesis, various inorganic and organic ALD/MLD precursors were studied with the aim to produce new luminescent hybrid inorganic-organic materials. The deposition of red-emitting phosphor represents the first described ALD/MLD made lanthanide-based luminescent hybrid material. Here, two different aromatic pyridine dicarboxylic acids were investigated as organic precursors together with Eu(thd)3. Oxygen-based 1,4-benzene dicarboxylic acid was used for comparison. Furthermore, the mixed (Y0.92Yb0.04Er0.04)(thd)3 precursor was used for the depositions together with 2,3-pyrazine dicarboxylic acid. Nucleic acid bases (uracil and adenine) were utilized for the first time as exciting natural organic precursors together with Na(thd), Ba(thd)2 and La(thd)3 metal precursors. For all the ALD/MLD processes investigated conditions were found under which the processes occurred based on well-controlled self-limiting surface reactions and yielded amorphous or crystalline hybrid thin films with growth rates typically ranging from 1 to 10 Å/cycle. The new lanthanide-based hybrid materials exhibited high luminescent intensities in the visible and near-infrared regions. The best luminescent intensities were achieved due to by-coordination to N and O of pyridine carboxylates. Furthermore, the (Y,Yb,Er)-based hybrid materials demonstrated upconverting properties with all the three main colours (red, green and blue). The nucleobases were found to form hydrogen-bonded hybrid networks which showed emission in the visible range, the color changing from blue (Na) to green (Ba) and greenish blue (La) depending on the metal constituent. Hydrogen bonding between the inorganic and organic moieties moreover caused the so-called red-edge shift (REES) effect rarely seen for conventional materials.