Photoluminescence Properties of Manganese-Doped Zinc Selenide Quantum Dots

Mn2+-doped II−VI semiconductor quantum dots reveal remarkably intense photoluminescence with a short lifetime associated with the 4T1(4G) → 6A1(6S) transition, which is spin-forbidden and is allowed because of crystal field effects. We explored the photophysical properties of high-quality, narrow-size-distribution Mn2+-doped ZnSe (ZnSe:Mn2+) quantum dots. ZnSe:Mn2+ quantum dots with varying amounts of dopant were studied at temperatures down to 10 K. Substitutional incorporation of Mn2+ 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:Mn2+ quantum dots show Mn2+-related orange luminescence. PLE measurements were carried out at a fixed emission wavelength related to Mn2+ orange luminescence. Five excited states corresponding to Mn2+ d−d transitions were observed. The crystal field strength (10Dq) increases with increasing Mn2+ concentration, increasing size, and decreasing temperature. In contrast to earlier conjectures about transition-metal-doped quantum dots, Mn2+-related photoluminescence feature could be observed in ZnSe:Mn2+ 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:Mn2+ quantum dots was also compared with that of their bulk counterpart.