Thermal quenching of fracto-induced mechano luminescence emission in (ZnS : ZnO): Cu phosphors

Studies on the temperature quenching of fracto-induced mechano luminescence (ML) emission of II-VI compounds with. reference to mixed zinc sulphide-ox ide powder phosphors activated with copper have been carried out by an impa ct of a moving piston on the phosphors under varying conditions of sample p reparation. A comparative study of temperature dependence of. electro lumin escence (EL) and photo luminescence (PL) of (ZnS:ZnO):Cu powder phosphors R ave also been investigated. It has been observed that the luminous intensit y decreases with temperature of the phosphor and disappears beyond a critic al temperature in all the 3 cases. The temperature dependence of mechano lu minescence (ML) in the present case follows the relation I(T)=I-o(1-T/T-c(m ) where n has the value around 1.2 and T-c being the critical temperature a t which the ML disappears. The decrease in ML intensity is at a faster rate (time-wise) than in EL and FL. The peaks corresponding to transient and de layed emissions in the ML intensity curves shift towards longer time scale as temperature is increased. Though the overall shape of the ML intensity v ersus time curves remains the same at different temperatures, the peak corr esponding to delayed ML emission undergoes considerable decrease with rise in temperature. The faster rate of decrease of ML intensity with temperatur e suggests that in addition to increase in the non-radiative transition pro bability, other parameters responsible for ML excitation such as surface ch arge density, piezo-electric constants etc. are also affected by temperatur e.