Luminescence Centers in Diamonds

The N3 optical center is one of the best known in steady-state luminescence spectra diamond. It is connected with three substitutional nitrogen atoms botmded to a common carbon atom or a vacancy, the ground state being a level and the excited state where luminescence originates a state (C3V point group). The zero-phonon line occurs at 2.985 eV and absorption and emission spectra show very closely a mirror relationship (Bokii et al. 1986). The N3 prompt luminescence decay is exponential and equal to 40 ns. Time-resolved luminescence spectroscopy enables to detect that N3 center has some metastable levels between the emitting and ground state. One of the decay paths of these metastable levels is delayed N3 luminescence, which occurs 

Our study of time-resolved luminescence of diamonds revealed the similar behavior (Panczer et al. 2000). Short-decay spectra usually contain N3 luminescence centers (Fig. 5.115a, b) with decay time of x = 30-40 ns. Despite such extremely short decay, sometimes the long-delay spectra of the same samples are characterized by zero-phonon lines, which are very close in energy to those in N3 centers. At 77 K = 308 nm excitation decay curve may be adjusted to a sum of two exponents of Xi = 4,2 ps and T2 = 38.7 ps (Fig. 5.115c), while at 300 K only shorter component remains. Under Aex = 384 nm excitation even longer decay component of T3 = 870 ps may appear (Fig. 5.115d). The first type of long leaved luminescence may be ascribed to 2.96 eV center, while the second type of delayed N3 luminescence is ascribed to the presence of two metastable states identified as quartet levels at the N3 center. 

---

The luminescence of diamonds is related to various defects in its structure. Almost always, luminescence centers in diamonds are related to N atoms. It is logical, because the atomic radii of C and N are nearly equal (approximately 0.77 A). Luminescence spectroscopy has proven to be the most widely used method in studies of diamonds even in comparison with optical absorption, ESR, IR and Raman spectroscopies. Himdreds of spectra have been obtained, fluorescence characteristics enter into diamond quality gemological certificates, a wide range of electronic and laser applications are based on diamond optical properties in excited states nitrogen center aggregation is controlled by the residence time of diamond in the mantle, distinction between natural... 

Fig. 5.69. a-d Laser-induced time resolved luminescence of N3 center in diamond (a, b) and decay times (c, d)... 

Fig. 2. Temperature dependence of the homogeneous width (a) and the peak shift (b) of the 637 nm zero-phonon line in luminescence spectrum of N-V centers in diamond films points experiment the line theoretical approximations according to the laws y — y0 + aT3 + bT1 and 8 = fiT2 - vT4.

Panczer G, Gaft M, Marfunin A (2000) Systems of interacting luminescence centers in natural diamonds laser-induced time-resolved luminescence and cathodoluminescence spectroscopy. In Pagel M, Barbin V, Blanc P, Ohnenstetter D (eds) Cathodoluminescence in geosciences. Springer, Berlin, pp 359-373... 

Panczer G, Gaft M, Marfunin A (2000) Systems of interacting luminescence centers in natural diamonds laser-induced time-resolved luminescence and cathodoluminescence spectroscopy. 

Pereira E, Monteiro T (1991) Delayed luminescence of the H3 center in diamond. J Lumin 48 9 814-818... 

The H3 center is well known in the steady-state luminescence spectra of diamonds. It belongs to the C2v point group, the ground state being level and the excited state from which luminescence takes place a Bi. Both emis-... 

Diamond luminescence was studied mainly with the two following aims to carry out a fundamental investigation of its physical properties and to determine the optimal conditions for luminescent sorting of diamond bearing rocks. For the first task, diamond photoluminescence was studied at liquid nitrogen temperature at which luminescence centers are marked by characteristic zero-phonon fines and are much more informative then at room temperature. For the second task, were diamond is one of the first minerals for which luminescence sorting was used, liuninescence properties should be studied at 300 K. In the first stages it was established that X-ray luminescence of the A-band... 

Walker J (1979) Optical absorption and luminescence in diamond. Rep Progr Phys 42 1605-1659 Walker G, Kamaluddin B, Glynn T, Cherlock R (1994) Luminescence of Ni centers in forsterite (Mg2Si04). J Lumin 60 61 123-126... 

It demonstrates that time-resolved luminescence of diamond is much more informative for ID task than the steady-state one. Vast amount of luminescence centers are known in natural diamonds (Zaitsev 2005) and if the specific diamond... 

Diamonds belonging for the second grope has low and very similar Raman/ Luminescence ratios, namely between 0.13 and 0.2. To differentiate between those diamonds several additional spectral features may be used. N3 is the only luminescence center with an appreciable fine structure at 300 K, while its zero-phonon line at 415 nm is characterized by different intensities down to practically total disappearance. For example, the ratio between the maximum intensity of N3 band at 440 nm and the 415 nm line intensity is changed in studied samples between 1.7 and 1.2. Figure 6.34 demonstrates the comparison between two samples with similar Raman/Luminescence ratio and even similar absolute intensity, while the ratio of... 

I440/I415 is substantially different. Another parameter is decay time of diamonds fast blue luminescence, which is different in different samples and may be used for identification purpose. The main reason is that several luminescence centers exist with emission spectrum very similar to those of N3, but with longer decay time of 500-700 ns. Under steady-state conditions there is some superposition of luminescence and excitation spectra of N3 and this center and they cannot be spectroscopically separated. By time-resolved spectroscopy the centers were separated and the second one, named 2.96 eV was connected with A1 impurity. Figure 6.34b, c demonstrate that the ratio between the second and the third components in kinetic series with delay difference between them of 10 ns is different, which evidently connected with the presence of N3 and 2.96 eV centers together, but in different ratios. 

It appears that there are A-bands of different nature. One of the A-band model is radiative recombination at dislocations. This model concerns a relatively narrow A-band peaked at 440 nm. This band is usually observed in low-nitrogen type 11 diamonds. There is a dislocation related model of the A-band considering luminescence on pure non-decorated dislocations excluding D-A recombination. This model is used for the A-band with a maximum at 415 nm. The second model of the A-band is intra center transitions at the B1(N9) centers (platelets). This model relates to the broad A-band with a maximum at 480 nm observed in natural type I diamonds. 

---