The influence of pressure on recombination centres in piezoelectric luminophores

Luminescence induced by elastic deformation of ZnS:Mn nanoparticles

“…The appearance of elastico ML in ZnS:Mn nanocrystals indicates that the local electric field near Mn 2 + ions should be higher because of the local change in the crystals-structure near Mn 2 + sites, where the piezoelectric constant should be higher. The change in the local structure near the impurities has been reported by many workers [17,52] and the possibility of the higher piezoelectric constant near the impurity centres has also been reported [31,32]. If there is nearly 3 to 4 times increase in the piezoelectric constant near the Mn 2 + centres, then the electric field of the order of 10 5 V cm À 1 may be produced, which may cause sufficient decrease in the trap-depth and subsequent electron-hole recombination may release energy non-radiatively for the excitation of Mn 2 + centres.…”

“…As ZnS crystals are non-centrosymmetric [30], the piezoelectrifiction caused by elastic deformation may give rise to the light emission [22,[31][32][33][34][35][36]. The other possibility for the occurrence of ML in ZnS:Mn nanocrystals may be the electrostatic interaction between charged dislocations and filled electrons traps [1,20,21,[37][38][39][40].…”

“…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 [22,[31][32][33][34][35][36] 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. Chudacek [31] has reported that the piezoelectric field produced by the deformations of ZnS crystals is less to cause ML, and he has suggested that the local piezoelectric field near the defect centres may be higher and it may produce ML.…”

Progress in triboluminescence-based smart optical sensor system

“…The local electric field near Mn 2 þ ions may, however, be higher because of the local change in the crystals' structure near Mn 2 þ sites [28,53]. This may result in a higher piezoelectric constant near the Mn 2 þ sites [54,55] to generate an electric field of the order of 10 5 V cm À 1 that may cause sufficient …”

Development of mechanoluminescence technique for impact studies

“…The suitability of the localized piezoelectrically induced detrapping model of EML becomes evident from the following facts: (i) the piezoelectric constant is higher near the defect centers [35], (ii) although ZnS is piezoelectric, it shows EML only in the presence of particular dopants such as Mn 2 þ , and it does not show EML in pure form and also for the Cu 1 þ or Ag 1 þ dopants, (iii) several crystals exhibit FML and EML in impure form and when they are purified, they do not show ML [1,9,[36][37][38], (iv) generally, the crystals show EML only in the presence of particular activator ions, (v) only the piezoelectric phase of Eu 2 þ -doped strontium aluminates shows EML and the nonpiezoelectric phases do not show EML and (vi) according to the localized piezoelectrically induced detrapping model, the total EML intensity should increase quadratically with the applied pressure, which is fairly in accord with the experimental observation.…”