The Triboluminescence of Zinc Sulphides and Alkali Halides

Abstract

Zinc SulphidesIn order to explain the detailed mechanism of TL, the triboand photoluminescence (PL) spectra were recorded for ZnS:Mn with Mn concentra- Cu, C1. TheWe obtained the following results:1. No spectral lines of gas-discharge were found. 2.In all TL-spectra only P1-bands were observed.3. ZnS:Mn and ZnS-Ag showed the same TL-and PL-spectra, if small shifts in emission bands are neglected. 4.The TL-spectra of ZnS:Cu and (ZnCd)S:Cu exhibited a greater intensity ratio 5. Q of ZnS:10-3 Cu, C l is a function of mechanical stress time.6. Compared to the PL, the TL-band shows a shift which can be attributed to of the blue to green band (Q = I,, /I than the PL-spectra.1 gJ the high mechanical stresses during impact (2).With these results it has been proved that the TL of zinc sulphide powders results mainly from a solid &ate luminescence. To explain the mechanism of TL, electroluminescence (EL) spectra were recorded with varying field frequency. In addition the TL-intensity and stress, measured with piezoelectrics, were recorded simultaneously with a double-beam oscilloscope.In accordance with the results of (3) and (4) the ratio Q for ZnS:Cu, C1 was very strongly dependent on the field frequency f. Therefore it was possible to identify the TL-spectra in the power jet of the mill with the EL-spectra. at 15 kHz (Fig. 1).The identity between TL-and EL-spectra can be explained only if on6 assumes an

Mechanoluminescence of Nanoparticles

“…The values of and are determined using Eqs. (37) and (38 ), ,respectively and they are found to be 0.045 ms -1 and 0.013 ms -1 for ZnS:Mn nanocrystals. and SrAl 2 O 4 :Eu, respectively.Thus,the value of r =1/ , comes out to be 22.22 ms, and the value of s =1/ , comes out to be 22.22 ms.…”

“…As ZnS crystals is non-centrosymmetric [33], the piezoelectrifiction caused by elastic deformation may give rise to the light emission [19,[34][35][36][37][38]. The other possibility for the occurrence of ML in ZnS:Mn crystals may be the electrostatic interaction between charged dislocations and filled electrons traps [1,4,[39][40][41][42][43].…”

“…The crystals of ZnS:Cu and ZnS:Ag do not show elastico ML because the local piezoelectrification near Cu and Ag centres may not be sufficient for causing the detrapping of electrons from the filled electrons traps. Although, in the past many workers [6,19,[34][35][36][37][38] have reported the piezoelectric origin of ML, primarily on the basis of the similarity between the waveforms, spectra, temperature dependence and other characteristics of ML and EL, no attempt has been made regarding the field ionization of traps and impact excitation or ionizations of luminescence centres under internal piezoelectric field.…”

Mechanoluminescence

“…EML may also be useful in radiation dosimetry (Chandra and Bisen, 1992). When an image is projected onto a yirradiated CsBr crystal using F-light and the crystal is squeezed sometime later, the part that had been exposed to F-light shows quite bright ML and reproduces the image (Meyer and Winnacker, 1982). This shows that with proper development this technique may be useful in photography as well as in the writing of secret messages.…”

“…Techniques used for deforming the crystals in ML measurements are: (1) compression (Chandra and Zink, 1980a,b); (2) bending (Alzetta et aI., 1970); (3) stretching (Crasto et al, 1987;Grabec, 1974;Parfeev et al, 1988); (4) loading (Chandra and Elyas, 1979;Atari, 1982;Atari and Ramani, 1986;Eid et al, 1986); (5) piston impact or impulsive (Chandra, 1983); (6) needle impact (Meyer and Polly, 1965); (7) cleaving and cutting (Longchambon, 1925;Batylin et aI., 1992;Dickinson et al, 1990;Meyer et al, 1970b;Chapman and Walton, 1983a,b); (8) laser (Hardy et aI., 1979); (9) shaking (Copty-Wergles et ai., 1990); (10) air-blast (Longchambon, 1925;Sodomka, 1968;Meyer and Obrikat, 1969); (11) scratching (Nakayama et aI., 1992); (12) grinding and milling (Inoue et aI., 1939); and (13) tribo or rubbing (Zhenyi et aI., 1995;Meyer et al, 1970;Keszthelyi and Bard, 1973;Orel et aI., 1989).…”