Photoluminescence spectra, doped

The zone of recombination can be very small as was shown by Aminaka et al. [225] by doping only a thin layer (5 nm) in the device by a red emission material. By observing the ratio of host and dopant emission, the authors were able to show that the recombination zone of the device was as thin as 10 nm. The emitted light is usually coupled out at the substrate side through the transparent anode. As a rule, the electroluminescence spectrum does not differ much from the photoluminescence spectrum. 

Figure 58 shows the photoluminescence spectrum of the undoped MgO degassed at the same temperature as the methane oxidative coupling reaction together with the photoluminescence speclrmn of the 3 mol% Li-doped MgO (Fig. 58, 2) and its deconvoluted curves (Fig. 58, 2-a and 2-b). In addition to a characteristic photolumincscence spectrum at around 370 nm, attributed to the surface sites in low coordination on MgO, the Li-doped MgO exhibits a new photoluminescence band at about 350-550 nm with a at about 450 nm (Fig. 58, 2-b). The intensity of this new emission depends on the amount of Li doped. The excitation spectr um corresponding to this new emission is evident at about 260-290 nm 100, 240), which suggests that surface sites with a coordination number of four may be associated with this new photoluminescence. 

Fig. 12.8 Guest-host system Spiro-60T Spiro-DPVBi absorption of guest and photoluminescence spectrum of host (a), spectral position of PL and AS E for different doping concentrations (b).

The photoluminescence emission and absorption spectra of MeLPPP films and solutions are essentially identical [123,124] and the EL emission spectrum matches the photoluminescence spectrum. The photoluminescence quantum efficiency (tjpl) was found to he as high as 30% for pure MeLPPP [125]. The photoinduced absorption spectrum of MeLPPP exhibits two distinct features, the triplet-triplet transition from l Bu to m Ag at 1.3 eVand the polaron band at 1.9 eV. The 2.1 eV band is a vibronic replica of the 1.9 eV band. These assignments were deduced from a comparison of the PA with doping-and charge-induced absorption spectra, which only yielded the 1.9 eV bands [126]. Due to the high localization of the TE wavefiinction, the triplet band only shows a vibronic progression of 80 meV [127],... 

Figure 14 Photoluminescence spectrum of an Al-doped 3C-SiC epilayer at 6 K, showing a series of...

At low temperatures, donors and acceptors remain neutral when they trap an electron hole pair, forming a bound exciton. Bound exciton recombination emits a characteristic luminescence peak, the energy of which is so specific that it can be used to identify the impurities present. Thewalt et al. (1985) measured the luminescence spectrum of Si samples doped by implantation with B, P, In, and T1 before and after hydrogenation. Ion implantation places the acceptors in a well-controlled thin layer that can be rapidly permeated by atomic hydrogen. In contrast, to observe acceptor neutralization by luminescence in bulk-doped Si would require long Hj treatment, since photoluminescence probes deeply below the surface due to the long diffusion length of electrons, holes, and free excitons. 

The introduction of electronic deep levels is demonstrated in Fig. 9 with low-temperature photoluminescence spectra for n-type (P doped, 8 Cl cm) silicon before (control) and after hydrogenation (Johnson et al., 1987a). The spectrum for the control sample is dominated by luminescence peaks that arise from the well-documented annihilation of donor-bound excitons (Dean et al., 1967). After hydrogenation with a remote hydrogen plasma, the spectrum contains several new transitions with the most prominent peaks at approximately 0.95, 0.98, and 1.03 eV. These transitions identify... 

For the samples comprising of PAA coated with Eu-doped xerogel typical PL spectrum measured at the excitation wavelength of 368 nm is presented in Fig. 2. It reveals the presence of clearly pronounced PL band at 475 nm visible to the naked eye which corresponds to inherent blue photoluminescence of PAA. Well-resolved optical band at 613 nm corresponding to Do-> F2 electron transition of Eu ions in the fabricated structure is also observed from the spectrum but red emission can not be seen with the naked eye. 

Fig. 1.10 Photoluminescence spectra of Er-doped Si02. One of the spectra is for the Er-doped Si02 located in a cavity resonant at 1540 nm. The other spectrum is without a cavity. The emission enhancement factor is 50 (after ref. [12]).

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