Yellow luminescence band

Doping ZnO with Li acceptor results in the YL band with a peak at about 2.2 eVand an FWHM of 0.5 eV, Ref [15]. In contrast to the GL band, the YL band decays very 

325 nm line of an HeCd laser (5 K). The inset shows a recombination model for the GL band peaked at 2.45eV. 

---

Fig. 5.65. Comparison of radiation-induced luminescence and EPR of different centers as a fimction of the heating temperature. Left integrated yellow liuninescence (upper) and EPR of TF, Yh, Nh and SiO (lower). Right yellow luminescence bands of different origin with different thermal stability (Gaft et al. 1986)...

The presence of a shallow acceptor level in GaN has been attributed to C substituting on an N site by Fischer et al [7], In luminescence experiments on GaN from high temperature vapour phase epitaxy in a C-rich environment donor-acceptor and conduction-band-to-acceptor transitions have been distinguished in temperature dependent experiments. From the separation of both contributions an optical binding energy of 230 meV close to the value of effective mass type acceptors was obtained. Hole concentrations up to 3 x 1017 cm 3 were achieved by C doping with CCU by Abernathy et al [10], In addition Ogino and Aoki [17] proposed that the frequently observed yellow luminescence band around 550 nm should be related to a deep level of a C-Ga vacancy complex. The identification of this band, however, is still very controversial. 

Besides REE, broad spectral bands characterize the luminescence of zircon. They are structureless down to 4.6 K, which makes difficult the correct interpretation of the nature of the luminescent centers. Different suppositions are made in previous studies and even the question about a yellow luminescence connection with intrinsic or impurity defect remains open. For example, the yellow band ( C-band ) was ascribed to SiO -defects (Votyakov et al. 1993 Krasnobayev et al. 1988) while the same emission ( band VII ) was explained by impurity luminescence, namely by Yb " " created by radioactive reduction of Yb " " (Kempe et al. 2000). 

Time-resolved luminescence spectroscopy of zircon revealed luminescence lines, which maybe confidentially ascribed to a Eu center (Fig. 4.38d). Usually they are hidden by a broad band yellow emission of zircon and may be detected only with a long delay time using its much longer decay time compared to yellow luminescence. 

Luminescence of Er " in the emission spectra of zircon is very difficult to detect under UV excitation even by time-resolved spectroscopy. The reason is that it has a relatively short decay time similar to those of zircon yellow luminescence, which usually is much stronger than Er " fines. Visible excitation, which is not effective for broad band luminescence, allows the revealing of Er " " luminescence fines, using high-resolution steady-state spectroscopy (Fig. 4.38f). 

Cerussite is characterized by several broad luminescence bands in the green-yellow part of the spectrum with different decay times (Fig. 5.52). Those bands are not confidently interpreted yet and only recently the idea of Ag or Cu participation has been proposed based on their close radii with Pb " (Gorobets and Rogojine 2001). We think that such interpretation is principally logical and has to be checked, but the possible participation of intrinsic lead also may be considered. 

Figure 4.39a represents the liuninescence band detected in all investigated natural zircons. It has an excitation band peaking at 310 nm. The broad yellow band at 575 nm with a decay time of 25-35 ps represents classical zircon luminescence. The picture is not principally changed with different delay times and gate width. After heating the sample up to 700 °C the luminescence intensity is nearly the same, but after that it is strongly reduced and at 800 °C the yellow luminescence disappears. Luminescence spectra at 77 and 4.2 K are not substantially different. 

FIGURE 6 Cathodoluminescence spectra obtained in the defective area of the crystal which appeared yellow in an optical microscope (a) and in the transparent area of the crystal (b). Note changes in the intensities of the yellow luminescence peak (2.4 eV) and band to band luminescence (3.5 eV). 

The yellow luminescence (YL) in GaN is a broad luminescence band centred around 2.2 eV. The YL appears to be a universal feature it has been observed in bulk GaN crystallites as well as in epitaxial layers grown by different techniques. The intensity can vary over a wide range, with good samples exhibiting almost no YL. 

FIGURE 1 Schematic illustration of levels involved in the yellow luminescence in GaN. Gallium vacancies introduce a deep acceptor level about 1.1 eV above the valence band Transitions between shallow donors and the deep acceptor level give rise to the YL. 

The emission and excitation spectra of yellow luminescence due to 82 in scapolite were observed at 300, 80 and 10 K (8idike et al. 2008). Emission and excitation bands at 10 K showed vibronic structures with a series of maxima spaced 15—30 and... 

The emission and excitation spectra of yellow luminescence due to 82 in scapolite were observed at 300, 80 and 10 K (8idike et al. 2010b). Emission and excitation bands at 10 K showed vibronic structures with a series of maxima spaced 15-30 and 5-9 nm, respectively. The relative efficiency of yellow luminescence from one scapolite sample was increased up to 117 times by heat treatment at 1000 °C for 2 h in air. The enhancement of yellow luminescence by heat treatment was ascribed to the alteration of 803 and 804 to 82 in scapolite. 

In the solid state, the complexes exhibit a yellow-green luminescence under UV irradiation (365 nm). All the emission spectra are similar and consist of three broad emissions above 370 nm (e.g., 384, 490 and 524 nm for m = 10, w = 6), while the free isocyanides (white solids) are luminescent giving one strong emission band with its maximum at about 360 nm. In dicMoromethane solution both the free isocyanides and their gold complexes are luminescent too, but only one intense emission is observed for the complexes in the range of 345-387nm (Figure 8.14). The lifetime... 

---