The impact of 1 wt% of Ir(ppy) 3 on trapping sites and radiative recombination centres in PVK and PVK/PBD blend seen by thermoluminescence

Blue iridium complexes as electron trapping sites and efficient recombination centres in poly(N-vinylcarbazole) seen by spectrally resolved thermoluminescence

“…Thus, taking into account the observations presented above, we can suppose that the iridium complex molecules work as dominant emission centres in the system. A similar effect has been previously observed for PVK and the mixture of PVK/PBD doped with Ir(ppy) 3 [18] and PVK with Ir(btp) 2 (acac) [19].…”

“…The high temperature maximum originates from excimer traps and the lower temperature (below 50 K) is connected with monomeric triplet states of carbazole groups. Moreover, our previous partial heating experiments confirm the presence of two main trapping levels: around 50 meV and 200 meV corresponding to low and high-temperature TL maxima, respectively [18].…”

“…The heating rate during SRTL runs was 7 K/min. The detailed SRTL procedure of experiment was described previously [17,18]. From the same solutions used for the fabrication of sample for SRTL experiments, thin layers (about 100 nm) were deposited by spin coating on quartz substrates for spectroscopic experiments.…”

“…Our previous studies of SRTL for PVK doped with Ir(ppy) 3 or Ir (btp) 2 (acac) show that the molecules of these dopants create deep trap states for holes in the matrix [18,19]. Moreover, even at 1 wt% of the dopants, emission originates almost exclusively from triplet excitons of the iridium complexes molecules.…”

“…Simultaneous registration of spectral distribution of the light emitted during the whole TL experiment allows identifying the origin of radiative recombination centres during detrapping processes. Therefore, the spectrally resolved thermoluminescence (SRTL) technique is applied for investigation of electroluminescent materials, especially emission layers based on host-quest systems [17,18].…”