Electroluminescence , origin

Luminescence covers all emissions of light in the near IR, VIS and near UV spectral regions. The origin of the luminescence can be specified as photoluminescence , electroluminescence , chemiluminescence , or bioluminescence for example. These definitions depend on the mode of formation of the excited molecule which eventually emits the luminescence. 

ALE was originally developed to meet the needs of improved ZnS thin films and dielectric thin films for electroluminescent thin film display devices. As an illustration of the ALE process, figure 13.11 summarizes the basic sequences of ALE in two alternative ways for producing ZnS. 

Figure 26 Emission spectra (PL, EL) in PC at room temperature of 40 wt% TPD donor solution with a 40 wt% of PBD acceptor added. The photoluminescence (PL) spectrum excited at 360 nm, the electroluminescence (EL) spectra (I, II) originate from the recombination radiation in a 60 nm thick film, taken at two different voltages. Absorption (Abs) and PL spectra (excitation at 360 nm) of (75wt% TPD 25wt% PC) and (75wt% PBD 25wt% PC) spin-cast films are given for comparison. Molecular structures of the compounds used are given in the upper part of the figure TPD [N,Nf-diphenyl-A v/V/-bis(3-methylphenyl)-l,l -biphenyl-4,4 diamine PBD [2-(4-biphenyl)-5-(4- er .-butylphenyl)l,3,4-oxadiazole PC[bisphe-nol-A-polycarbonate]. Adapted from Ref. 112.

Our recent results further proved that the neutral ligands used in terbium complexes strongly affected their photoluminescence and electroluminescence performances. For the complexes Tb(tba-PMP)3(TPPO), Tb(tba-PMP)3(H20), and Tb(tba-PMP)3(phen) (compounds 40-42), the integral emission intensities are very different and in the ratio 2.1 1.3 1 for 40, 41, and 42, respectively (Figure 11.23). Obviously, this difference originated from the different... 

FIGURE 4.13. Normalized electroluminescence spectra of Alq/NAPOXA/TAD LEDs as a function of NAPOXA thickness x (in X). In the inset is shown the fraction of the total LED light output originating in the Alq as a function of x together with a fit to the data points. 

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