3.4. Decay rate spectra analysis
The fluorescence lifetime is defined as the time required for the fluorescence intensity to decay down to 1/e of its initial value. Fig. 6 shows the decay curve of the emission transitions of CaZnBP glass doped different mol% of Mn2+ ions. From the results, the lifetimes of the glass samples are shorten as the concentration of the Mn2+ ions increases. Therefore, the optimum concentration of Mn2+ ions in this glass sample will be 2 mol% (26.7 ms). At room temperature the lifetime is reduced by thermal quenching, which has been found to be sample dependent. The concentration also influences the lifetime; even at Mn2+ concentrations as low as 1% a reduction in the lifetime has been reported [56]. In our case, the lifetime of the decay curves of the emission transition of Mn2+ ions decreased when the concentration Mn2+ ions increases (Fig. 6). It is known that due to exchange interaction the spin selection rule is partially lifted and the 4T1g (G) → 6A1g (S) transition in the Mn2+ becomes more allowed at higher Mn2+ concentrations [57]. This results in the fact that the lifetime of the Mn2+ emission will be reduced at higher Mn2+ concentrations when exchange coupled Mn2+ pairs are formed