Photoluminescence Properties of Manganese-Doped Zinc Selenide Quantum Dots

Mn 2+ -doped II−VI semiconductor quantum dots reveal remarkably intense photoluminescence with a short lifetime associated with the 4 T 1 ( 4 G) → 6 A 1 ( 6 S) transition, which is spin-forbidden and is allowed because of crystal field effects. We explored the photophysical properties of high-quality, narrow-size-distribution Mn 2+ -doped ZnSe (ZnSe:Mn 2+ ) quantum dots. ZnSe:Mn 2+ quantum dots with varying amounts of dopant were studied at temperatures down to 10 K. Substitutional incorporation of Mn 2+ in ZnSe quantum dots was confirmed by electron paramagnetic resonance measurements as well. Photoluminescence emission (PL) and photoluminescence excitation (PLE) spectroscopies at low temperature were employed to examine the sp−d interactions. PL measurements of ZnSe:Mn 2+ quantum dots show Mn 2+ -related orange luminescence. PLE measurements were carried out at a fixed emission wavelength related to Mn 2+ orange luminescence. Five excited states corresponding to Mn 2+ d−d transitions were observed. The crystal field strength (10 Dq ) increases with increasing Mn 2+ concentration, increasing size, and decreasing temperature. In contrast to earlier conjectures about transition-metal-doped quantum dots, Mn 2+ -related photoluminescence feature could be observed in ZnSe:Mn 2+ quantum dots even when the excitation energy was lower than the forbidden gap but was equal to the energy of the d−d transitions. The behavior of ZnSe:Mn 2+ quantum dots was also compared with that of their bulk counterpart.