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Luminescent materials play increasingly important roles in our lives. Improvements in these materials’ quantum efficiencies (QEs), costs and toxicity can greatly reduce the power consumption, price and environmental damage to the planet, respectively. Carbon quantum dots (CQDs) and luminescent materials exhibiting thermally activated delayed fluorescence (TADF) are two interesting materials in these aspects. Furthermore, measurements on electrochemiluminescence (ECL) and electroluminescence of these luminescent materials can quickly evaluate their performance for many applications. In this thesis, controlled CQD syntheses are revealed beneficial to luminescent materials applications. Their film ECL demonstrated relatively stable anionic and cationic radicals leading to high emission at solid/solution interfaces. It has been found that small sizes of CQDs produce efficient bright white film emissions. It has been discovered that film ECL is similar to the light emitting layer in an LED and can be used to find surface states in these CQDs that are predominantly excited to generate a wavelength-potential applied relationship. Combining this knowledge, small emitting CQDs have been analyzed using synchrotron spectroscopy, where thiophene states were uniquely found and likely caused the solid-state emissions and high cationic radical stability, both through cation-pi interactions. For the first time, CQD light emitting devices have been constructed to achieve 1 cd/m2 blue emissions for 3 h at a constant potential of 7.0 V. Electrochemical impedance spectroscopy has been utilized to display the possibility that device failure is due to small ions reacting at the highest energy interface. Organic long-persistent ECL has been observed for the first time with several TADF molecules. This phenomenon has occurred likely because of an exciplex being formed with a compound that had a small singlet-triplet energy gap. Two simple methods have been developed in this thesis to determine the absolute ECL QE of compounds along with the common commercial emitter Ru(bpy)32+. Finally, an analytical strategy has been established for measuring QEs of indicator and lighting LEDs in high accuracy and precision. |
