The nature of trapping sites and recombination centres in PVK and PVK–PBD electroluminescent matrices seen by spectrally resolved thermoluminescence

• Published in: Journal of physics. D, Applied physics Vol. 43; no. 29; p. 295101
• Main Authors: Glowacki, Ireneusz, Szamel, Zbigniew
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 28.07.2010; Institute of Physics
• Subjects: Blends; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electroluminescence; Exact sciences and technology; Excimers; Materials science; Mathematical analysis; Matrices; Matrix methods; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other luminescence and radiative recombination; Other materials; Physics; Polyvinyl carbazole; Specific materials; Spectra; Thermoluminescence; Temperature dependence; Oxadiazoles; Radiative recombination; Electroluminescence; Singlet state; Monomers; Thin films; Triplet state; Carbazoles; Trapping; Traps; Polymers; Deep level; Thermoluminescence
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/43/29/295101

Two electroluminescent polymer matrices poly( N -vinylcarbazole) (PVK) and PVK with 40 wt% of 2- tert -butylphenyl-5-biphenyl–1,3,4-oxadiazole (PBD) were studied using spectrally resolved thermoluminescence (SRTL) in the temperature range 15–325 K. The comparison of the SRTL results with the electroluminescence (EL) spectra has allowed identification of the localized (trapping) sites and the radiative recombination centres present in the investigated matrices. In the neat PVK films deep traps with a depth about 200 meV, related to triplet excimers dominate, while in the PVK–PBD (40 wt%) blend films the traps that are related to triplet exciplexes formed by the carbazole groups and the PBD molecules dominate. Depth of the traps in the PVK–PBD blend is somewhat lower than that in the neat PVK. An analysis of the EL spectra shows that in the PVK and in the PVK–PBD blend the dominant radiative centres are singlet excimers and singlet exciplexes, respectively. However, in the neat PVK some contributions of the triplet monomer and the triplet excimer states in the EL were also detected.