Photoluminescent Characteristics Of MgAl₂O₄:Mn₂₊ Under Blue Excitation

The focus of my research is to study the photoluminescent properties ofMgAl_2O4:xMn²⁺under the excitation of blue light. And a new explanation whyluminescent intensity decrease when x>10%has been put forward.Firstly, the photoluminescence of MgAl₂O₄:Mn²⁺in room temperature is studied.It is found that Mn2+occupies the tetrahedron site in the host of MgAl2O4and theemission of Mn2+peaks at520nm. The photoluminescence excitation spectrum ofMn2+shows that MgAl₂O₄:Mn²⁺is a promising candidate for blue light excitedluminescent materials because there are two excitation peaks at425nm and450nm.Green and red phosphors suitable for blue light excitation are excellent ways tomanufacture solid state lighting devices in longer wavelength. By changing thedoping concentration of Mn2+, the optimal concentration for strongest luminescenceis found to be10%.Secondly, the reason why the luminescence intensity of MgAl₂O₄:xMn²⁺decrease after x>10%has been carefully studied. The lifetimes of Mn²⁺are requiredby time-resolved photoluminescence measurement. Through the comparisonbetween calculated values and experimental values, it is clear that concentrationquenching effect is not sufficient to explain the fact that the luminescence intensityof MgAl2O4:xMn2+decrease after x>10%alone. So the diffuse reflectionmeasurements are carried out. From the room temperature diffuse reflection spectrum, it is clear that the defects compete with Mn²⁺for the excitation photonicsand reabsorb the520nm emission from Mn²⁺.Finally, we studied the temperature dependent photoluminescence ofMgAl₂O₄:10%Mn²⁺. When the temperature rises from300K to500K, theluminescence intensity of Mn²⁺does not decrease. On the contrary, the luminescenceintensity increases slightly at high temperature. This shows that MgAl₂O₄:10%Mn²⁺possesses an excellent thermal stability. In order to explain this thermal stability,temperature dependent photoluminescence measurements are carried out. From thetemperature dependent photoluminescence spectrum, it is obvious that the absorptionof defects in the range from300nm to700nm is reduced along with the increase oftemperature. In other words, the absorption competition and re-absorption processesare reduced at high temperature.