Temperature and pressure dependences of the Mn ²⁺ and donor-acceptor emissions in ZnS:Mn ²⁺ nanoparticles

Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn ²⁺ nanoparticles. As temperature increases, the donor-acceptor (DA) emission of ZnS:Mn ²⁺ nanoparticles at 440 nm shifts to longer wavelengths while the Mn ²⁺ emission ( ⁴T ₁- ⁶A ₁) shifts to shorter wavelengths. Both the DA and Mn ²⁺ emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn ²⁺ emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn ²⁺ nanoparticles is approximately -3.2meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn ²⁺ emission in ZnS:Mn ²⁺ nanoparticles is roughly -34.3meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn ²⁺ ions is mainly from the recombination of carriers localized at Mn ²⁺ ions.