Study On The Preparation And Properties Of Mn⁴⁺ Doped Sr_2-xBa_xMg Ge₂O₇ Phosphor

In recent years,white light-emitting diodes（WLEDs）have been widely used in daily lighting,almost replacing fluorescent tubes and traditional incandescent lamps.Compared to the latter two,WLEDs have a longer lifetime and lower energy consumption.Currently,the mainstream white LED products usually lack a red component,which results in higher correlated color temperature（CCT）and lower color rendering index（CRI）.In order to solve this problem,developing red phosphors for WLED is demanding.Mn⁴⁺doped crystal materials show wide absorption band in UV-blue light region and a strong red emission in the range of 600～740 nm,very promising for WLED based lighting products.In this paper,focusing on Mn⁴⁺doped oxides,a new red inorganic phosphor system was developed by cationic doping and its properties were studied.Details are as follows:1、Preparation and property investigation of Sr₂Mg Ge₂O₇:x Mn⁴⁺red phosphors with different Mn⁴⁺ concentrations:Firstly,a series of red phosphors Sr₂Mg Ge₂O₇:x Mn⁴⁺were prepared by high temperature solid state method,and the structure and morphology of the materials were characterized by XRD and SEM.Then,the properties of these phosphors were studied.The results show that these phosphors contain two excitation bands（peak at 290 nm and 419 nm）;and attributing to the ²E→⁴A₂ transition of Mn⁴⁺ions,the phosphors exhibit two emission bands in the red region of 600-700 nm,with the peak at 664 nm and 630 nm.When the doping concentration of Mn⁴⁺at x=0.7%,the obtained phosphor has the best luminescence performance,the photoluminescence quantum yield is 33%,CIE coordinate is（CIEx=0.7217,CIEy=0.2783）.Moreover,at high temperature of 423 K,the emission intensity is still 96.5% of that at room temperature.2、Preparation and property investigation of novel phosphors of Sr_2-xBa_xMg Ge₂O₇:y Mn⁴⁺with different doping concentrations of Ba²⁺and Mn⁴⁺ions:Firstly,the concentration of Mn⁴⁺was fixed（y=0.8%）,and the phosphors Sr_2-xBa_xMg Ge₂O₇:y Mn⁴⁺with different Ba²⁺doping concentrations were prepared and their properties were studied.Compared with SMGO:Mn⁴⁺ phosphors without Ba²⁺doping,the Ba²⁺doped SBMGO:Mn⁴⁺phosphors have the same tetragonal crystal structure and similar excitation（paek at 290 nm and 419 nm）and emission spectra（600-700 nm）as SMGO:Mn⁴⁺phosphors,but their luminescence properties are better.The sample with the best luminescence performance has the doping concentration of Ba²⁺at x=0.1.Then,fixing the Ba²⁺at x=0.1 and changing the concentration of Mn⁴⁺,new phosphors were prepared to determine the best Mn⁴⁺ions concentration.Finally,the optimal ratio of the new phosphor was determined to be Sr_1.9Ba_0.1Mg Ge₂O₇:0.008Mn⁴⁺.The luminous quantum efficiency of this sample is as high as 88%,which is 2.67 times that of the phosphor without Ba²⁺ion doping,and a decay lifetime of 3.592 ms was obtained.More importantly,at high temperature of 423 K,the emission intensity is still 94.3%of that at room temperature,showing excellent thermal stability of emission.