Mn⁴⁺激活的典型LED红色荧光粉研究进展 增强出版

Mn 4+ 激活的典型LED红色荧光粉研究进展 Research Progress of Mn 4+ Activated Typical LED Red Phosphors 1 first-author 章伟(1998-)，男，安徽舒城人，硕士研究生，2020年于合肥工业大学获得学士学位，主要从事Mn4+掺杂LED红色荧光粉的研究。 E-mail: 22026049@zju.edu.cn http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210737&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210743&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210749&type= 章伟 (1998-)，男，安徽舒城人，硕士研究生，2020年于合肥工业大学获得学士学位，主要从事Mn 4+ 掺杂LED红色荧光粉的研究。 E-mail: 22026049@zju.edu.cn 22026049@zju.edu.cn 1 1 corresp E-mail: qiaoxus@zju.edu.cn E-mail: qiaoxus@zju.edu.cn 乔旭升(1980-)，男，河南洛阳人，博士，副教授，博士研究生导师，2007年于浙江大学获得博士学位，主要从事发光玻璃陶瓷、荧光粉与分子动力学模拟方面的教学与科研工作。 E-mail: qiaoxus@zju.edu.cn http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210754&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210758&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210763&type= 乔旭升 (1980-)，男，河南洛阳人，博士，副教授，博士研究生导师，2007年于浙江大学获得博士学位，主要从事发光玻璃陶瓷、荧光粉与分子动力学模拟方面的教学与科研工作。 E-mail: qiaoxus@zju.edu.cn qiaoxus@zju.edu.cn 1 浙江大学材料科学与工程学院　硅材料国家重点实验室，浙江 　 杭州 　 310027 浙江大学材料科学与工程学院　硅材料国家重点实验室，浙江 　 杭州 　 310027 State Key Laboratory of Silicon Materials & School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China State Key Laboratory of Silicon Materials & School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China Mn 4+ 激活的红色荧光粉具有宽带吸收、窄带发射、色纯度高以及成本低的特点，在白光发光二极管(Light emitting diode,LED)室内照明、农业上辅助植物生长、背光显示等领域的研究备受关注。本文综述了Mn 4+ 激活的典型LED用红色荧光粉研究进展。首先讨论了Mn 4+ 发光的晶体场理论，归纳了近来报道的Mn 4+ 激活氟化物与铝酸盐荧光粉；然后总结了如何从机理上优化光谱学性能、改善热猝灭性能和湿化学稳定性；最后说明了尚待解决的问题并展望了未来发展趋势。 Mn 4+ -doped red phosphors have attracted much attention in the fields of white LED indoor lighting, agricultural plant growth and backlight displaying, due to the advantages of broad-band absorption, narrow-band emission, high color purity and low cost. This work reviews recent progress of Mn 4+ activated typical LED red phosphors. First, the crystal field theory of Mn 4+ is discussed. Then, the research progress of Mn 4+ activated fluorides and aluminates is summarized. Next, how to improve luminescence performance, thermal stability and moisture resistance are discussed theoretically. Finally, the main problems in the development of Mn 4+ doped red phosphors are presented and the future trends are prospected. LED 光致发光 Mn 4+ 红色荧光粉 LED photoluminescence Mn 4+ red phosphors 1　引言 1 作为一种新型固态光源，基于p-n结芯片发光的发光二极管(LED)因光效高、寿命长、能耗低、环境友好等优点，被广泛应用在室内照明、背光显示、辅助植物生长等领域 [ 1 1 - 9 9 1-9 ] 。商用白光LED(WLED) 采用InGaN蓝光芯片与Y 3 Al 5 O 12 ∶Ce 3+ 荧光粉组合而成，其原理是荧光粉被蓝光芯片(约450~480 nm)激发而发射黄光，并与未被吸收的蓝光混合得到白光。这种荧光粉与蓝光/近紫外芯片组合产生白光的LED被称为荧光粉转换的LED(pc-LED)。然而，YAG∶Ce 3+ 缺少红光发射部分，导致上述WLED显色指数较低( R a < 80)和色温偏高(CCT > 4 500 K)，难以满足暖白光照明和宽色域液晶显示背光源的要求 [ 10 10 ] 。为了得到高显色指数与低色温的WLED或宽色域覆盖率的背光源，解决办法之一是引入红色荧光粉 [ 11 11 ] 。典型的LED红色荧光粉按照激活剂离子主要分为Eu 2+ 掺杂的(氧)氮化物、Mn 4+ 掺杂的氟化物与铝酸盐两大类 [ 12 12 ] 。以CaAlSiN 3 ∶E http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210768&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210779&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210774&type= 和Sr 2 Si 5 N 8 ∶E http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210785&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210794&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210790&type= 等为代表的第一类红色荧光粉，利用Eu 2+ 宇称允许的5d→4f跃迁，具有宽谱范围可调的发射带和高发光量子效率。然而，除了少数Eu 2+ 掺杂的(氧)氮化物荧光粉 (如UCr 4 C 4 结构的Sr［LiAl 3 N 4 ］∶E http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210798&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210808&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210803&type= 和Sr［Mg 3 SiN 4 ］∶E http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210812&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210823&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210818&type= ) 外，大多数都具有较宽的红光发射带，虽然适合照明应用场景，但却不太适合显示应用场景。同时，Eu 2+ 掺杂荧光粉较宽的激发谱带易与黄色或绿色荧光粉在混合使用时产生重吸收问题 [ 17 17 ] 。此外，其合成条件很苛刻，需要高温高压环境，如1 900 ℃和1 MPa的N 2 氛围 [ 18 18 ] 。因此，开发新型光效高、成本低、易制备的窄带红色荧光粉显得十分重要。 在该背景下，研究人员开发了第二类Mn 4+ 激活的红色荧光粉。Mn 4+ 在近紫外与蓝光区域由于自旋允许的 4 A 2 → 4 T 1 与 4 A 2 → 4 T 2 跃迁而产生宽带强吸收，在红光区域由于对格位晶体场不敏感的 2 E→ 4 A 2 跃迁而产生窄线状发射，且其自旋禁戒容易通过改变格位对称性而被打破，获得高效红光发射。与Eu 2+ 激活的红色荧光粉相比，Mn 4+ 激活的红色荧光粉与绿粉或黄粉匹配蓝光LED时重吸收效应不明显 [ 18 18 ] 。此外，Mn 4+ 激活的红色荧光粉原料与制备成本较低，合成条件温和，因而能够满足暖白光LED照明与宽色域显示背光源的要求。以Mn 4+ 作为激活剂的典型红色荧光粉主要包括Mn 4+ 掺杂的氟化物荧光粉和铝酸盐荧光粉。前者的最强吸收峰与蓝光芯片发射峰匹配，在暖白光照明和背光显示领域得到了商业化应用；后者的主激发峰在近紫外区域，化学稳定性优异，制备简单，在暖白光照明领域具有潜在的应用前景。 基于此，本文综述了Mn 4+ 激活的氟化物和铝酸盐荧光粉的研究进展。首先讨论了Mn 4+ 发光的晶体场理论，归纳了近来报道的Mn 4+ 激活氟化物与铝酸盐荧光粉；接着总结了如何从机理上优化光谱学性能、改善热猝灭性能和湿化学稳定性；最后说明了尚待解决的问题并展望了未来发展趋势。 2　Mn 4+ 发光的晶体场理论 1 Mn 4+ 最外层电子构型是3d 3 ，一般倾向于占据八面体格位，其能级结构可采用晶体场理论描述。3d 3 电子处于最外层，对晶体环境十分敏感。八面体格位的晶体场将五重简并的d轨道劈裂成二重简并的e g 和三重简并的t 2g 轨道。由于自旋-轨道耦合的作用，最外层电子组态将进一步劈裂成多重态。纯3d态之间只能发生磁偶极过程引起的辐射跃迁；但是，当离子占据的位置对中心对称发生偏离，使得其他组态混杂到3d组态，就可能发生电偶极跃迁。将能级与对应的晶体场强度绘制成图，则得到Tanabe-Sugano图 [ 19 19 ] 。 图1(a) 图1(a) 是八面体晶体场中Mn 4+ 的Tanabe-Sugano图，表示以Racah参数 B 为单位的能量 E 随晶体场强度 Dq / B 的变化。 Dq / B 是晶体场强度， B 和 C 是电子间排斥作用的Racah参数。从图中可知，Mn 4+ 的激发光谱通常是 4 A 2 → 4 T 2 、 4 T 1 ( 4 F) 和 4 T 1 ( 4 P) 三种可能的跃迁，其中， 4 A 2 → 4 T 1 ( 4 P) 会被主晶格吸收或电荷转移跃迁所影响。尽管自旋禁戒的跃迁强度很弱，只能通过精密度很高的仪器才能测量到，但有些基质的 4 A 2 → 2 T 2 在激发光谱中也有体现。激发到 4 T 1 与 4 T 2 能级上的电子会无辐射跃迁到 2 E，进而通过 2 E→ 4 A 2 产生红光发射。除 2 E和 2 T 1 能级与基质共价性紧密相关外， 大部分能级位置强烈依赖于晶体场强度。 Dq 与主要能级间的关系是: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210843&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210848&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210852&type= 在晶体场的对称性降低后，上述能级可进一步劈裂到许多亚能级。通常基态 4 A 2 和激发态 2 E都能分别劈裂成两个亚能级，从较低和较高的亚能级发射谱线分别叫做R 1 和R 2 零声子线(ZPLs)，如 图1(b) 图1(b) 所示。ZPL的发射强度由Mn 4+ 所处的局部晶体场环境对称性决定。当Mn 4+ 处于对称性高的立方结构时，样品ZPL发射强度很弱或接近零；而当Mn 4+ 处于对称性较低的三方、六方或正交晶系结构时，可以获得较强的ZPL发射 [ 20 20 ] 。不同种类的基质中，Mn 4+ 的ZPL以及它们的具体位置也是不同的 [ 21 21 - 23 23 21-23 ] 。 Racah参数 B 和 C 表示电子间排斥作用， B 越小，基质共价性越小。Brik等 [ 24 24 ] 同时考虑参数 B 和 C ，得出电子云膨胀效应参数 β 1 的经验公式( B 0 、 C 0 是自由离子Racah参数): http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210855&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210861&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210867&type= 其中，Mn 4+ 的 B 0 =1 160 cm -1 , C 0 =4 303 cm -1 。 B 、 C 可按下式计算: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210871&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210876&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210881&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210886&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210892&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210894&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210899&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210904&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210907&type= β 1 越小，基质共价性越强，比只用 B 判断可靠性更高。发射峰的位置受基质晶格的共价性影响，而与晶体场强度无关，共价性强的基质发射带偏向长波方向。 3　Mn 4+ 激活的氟化物荧光粉 1 Paulusz [ 26 26 ] 在1973年报道了一种新型氟化物荧光粉K 2 SiF 6 ∶Mn 4+ ，但当时还没有研制出蓝光LED芯片，并且该荧光粉在近紫外波段吸收较弱，故没有获得实际应用而未引起重视。Adachi [ 27 27 - 30 30 27-30 ] 从2008年起相继报道了K 2 SiF 6 ∶Mn 4+ 等一系列氟化物荧光粉，此后的十几年里，无论是在研究新型材料作为基质、改良制备方法还是在增强其抗湿性等方面，氟化物荧光粉都获得了长足的进步。 Mn 4+ 掺杂的氟化物荧光粉兼具蓝光波段宽带强吸收和发射峰窄(~3 nm) 两个优点，发射峰位于人眼敏感的630 nm左右，激发带位于450 nm左右，能够作为暖白光照明和背光显示的红色组分。已经报道的Mn 4+ 掺杂的氟化物荧光粉可以归纳为9类 [ 31 31 - 41 41 31-41 ] : (1) AB F 2 ∶Mn 4+ (如NaHF 2 ∶Mn 4+ ,KHF 2 ∶Mn 4+ ); (2) AB F 3 ∶Mn 4+ (如KZnF 3 ∶Mn 4+ ); (3) A 2 A'B F 6 ∶Mn 4+ (如K 2 NaAlF 6 ∶Mn 4+ , K 2 NaScF 6 ∶Mn 4+ ); (4) A 2 B F 6 ∶Mn 4+ ( A =Li,Na,K,Rb,Cs,NH 4 ; B =Si,Ge,Zr,Sn,Ti,Hf); (5) AB F 6 ∶Mn 4+ ( A =Ba,Zn; B =Si,Ge,Sn,Ti); (6) A 3 B F 7 ∶Mn 4+ (如K 3 SiF 7 ∶Mn 4+ ); (7) A 2 B F 7 ∶Mn 4+ (如K 2 NbF 7 ∶Mn 4+ , K 2 TaF 7 ∶Mn 4+ ); (8)多氟化物(如Na 3 HTiF 8 ∶Mn 4+ ,Ba 3 Sc 2 F 12 ∶Mn 4+ ); (9)氟氧化物(如Cs 2 NbOF 5 ∶Mn 4+ ,Na 2 WO 2 F 4 ∶Mn 4+ )。 A 2 B F 6 ∶Mn 4+ 系列红色荧光粉以K 2 SiF 6 ∶Mn 4+ (KSFM)为典型代表，在广色域背光显示领域逐渐取代了CaAlSiN 3 ∶E http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210911&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210920&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210916&type= 。K 2 SiF 6 为立方晶系，空间群 Fm http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210924&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210932&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210928&type= m ，晶格常数 a =0.813 nm,X射线衍射(XRD)图谱如 图2(a) 图2(a) 所示 [ 30 30 , 43 43 ] 。KSFM在日光下的外观颜色为橙色，主要制备方法有湿化学刻蚀法 [ 29 29 - 30 30 29-30 ] 、共沉淀法 [ 44 44 - 45 45 44-45 ] 、离子交换法 [ 25 25 , 46 46 ] 和水热法 [ 43 43 , 47 47 ] 。Adachi等 [ 30 30 ] 在HF/KMnO 4 混合溶液中用湿化学法刻蚀Si片制备出KSFM，但该方法原料成本高、产率低。Huang等 [ 43 43 ] 首次开发了绿色水热合成新路线，以常见的低毒H 3 PO 4 /KHF 2 液体代替高毒HF，使用SiO 2 、Mn L 2 ( L =HP http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210936&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210944&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210940&type= ) 为原料生产出KSFM荧光粉。 图2(b) 图2(b) 的微观形貌清晰地显示颗粒呈十面体形状，平均粒径约为10 μm，粒径分散较为均匀。由于八配位Mn 4+ 的有效离子半径是0.054 nm,［SiF 6 ］ 2- 的Si 4+ 半径是0.04 nm，因此Mn 4+ 可以占据K 2 SiF 6 基质的Si位，属于等价取代，不会造成电荷不平衡。但在湿化学合成过程中，Mn 4+ 易受环境的影响而变价成为其他价态，如M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210948&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210954&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210951&type= (0.083 nm) 或Mn 3+ (0.065 nm)等，它们有可能进入基质晶格中，恶化荧光粉的热稳定性和化学稳定性 [ 17 17 ] 。 图2(c)、(d) 图2(c)、(d) 中的每个Si 4+ 离子与6个F - 紧密配位，形成一个［SiF 6 ］ 2- 八面体；通过共用每个［SiF 6 ］ 2- 的3个F - ，每个K + 离子被4个［SiF 6 ］ 2- 八面体包围，形成一个［KF 12 ］十面体结构。KSFM的激发光谱是以350 nm和460 nm为中心的两个宽波段，460 nm处的最强激发带由若干小间距的组分组成，这种类似声子边带的结构可以理解为基频的振动过程与叠加在电子跃迁上的［SiF 6 ］ 2- (［MnF 6 ］ 2- )八面体不对称振动相结合的结果( 图2(e) 图2(e) ) [ 30 30 ] 。发射光谱的主要发射峰位于608,612,630,634,646 nm，对应着电子跃迁或电子振动跃迁，其中~612 nm和~634 nm处的发射是由于八面体的奇数振动在 2 E波函数中引入奇数项，使得产生允许的跃迁。在LED背光显示中，KSFM由于发射峰窄和无自吸收的特点而能实现高效率和宽色域显示 [ 12 12 ] 。和CaAlSiN 3 ∶Eu 2+ (半峰宽约86 nm) 相比，KSFM搭配β-SiAlON绿粉可获得≥90%NTSC值(即美国国家电视标准委员会制定的色域标准)，如 图2(f) 图2(f) 所示 [ 48 48 ] 。 表1 表1 列举了近来报道的Mn 4+ 激活氟化物荧光粉，可见在上述九大类氟化物荧光粉中，不同离子占据 A 位、 B 位时，能衍生出种类丰富的氟化物晶体结构。在其他类型的Mn 4+ 激活氟化物荧光粉中，比较典型的是Na 2 SiF 6 ∶Mn 4+ 、K 2 TiF 6 ∶Mn 4+ 、Cs 2 TiF 6 ∶Mn 4+ 、Na 2 TiF 6 ∶Mn 4+ 、K 2 GeF 6 ∶Mn 4+ 等高性能荧光粉，其内量子效率可超过90%。根据对光谱学性能的总结，可见氟化物系列荧光粉均能被350~370 nm的近紫外光和450~480 nm的蓝光有效激发，最强发射峰在620~640 nm。 表1 表1 所列氟化物荧光粉的 β 1 值均大于1，随着组分的变化不大，表明氟化物荧光粉的离子性较强。综上所述，氟化物荧光粉有如下优点:(1)发射峰的半峰宽较窄，且发射峰基本固定在630 nm左右。它们的半峰宽均小于30 nm，实际应用中光的二次重吸收少。(2)内量子效率高。大部分氟化物荧光粉的内量子效率高于60%，最高值甚至达到99.83%。但是，氟化物荧光粉同时也具有如下缺点:(1)抗湿性较差 [ 49 49 ] ;(2)制备过程用到的氟源和有机物容易污染环境，且制备步骤相对复杂，产率低；(3)外量子效率有待提高 [ 50 50 ] ;(4)荧光寿命较长 [ 51 51 ] 。 注： M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210978&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210983&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210981&type= 的发射波长是指M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210985&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210989&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210987&type= 发射强度最大值对应的波长，所有的数据都对应着一定浓度的M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210992&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210997&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210995&type= ，不同浓度的M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21210999&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211005&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211002&type= 发射强度不同。—表示无参考数据； * 指外量子效率，不加符号表示内量子效率。 1 1 Host 1 1 λ ex /nm 1 1 λ em /nm 1 1 Δ E /eV　 1 1 T 1/2 /K　 1 1 Dq / B 　 1 1 β 1 　 1 1 B /cm -1 　 1 1 QE/% 1 1 Reference 1 1 K 2 SiF 6 1 1 350; 460 1 1 632 1 1 — 1 1 453 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 53 53 ] 1 1 Li 2 SiF 6 1 1 350; 448 1 1 630 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 54 54 ] 1 1 Na 2 SiF 6 1 1 360; 467 1 1 629 1 1 0.217 8 1 1 — 1 1 3.61 1 1 1.02 1 1 593.1 1 1 99.83 1 1 [ 55 55 ] 1 1 Cs 2 SiF 6 1 1 357; 460 1 1 631 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 56 56 ] 1 1 BaSiF 6 1 1 360; 470 1 1 640 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 57 57 ] 1 1 BaGeF 6 1 1 366; 471 1 1 636 1 1 0.72 1 1 — 1 1 3.79 1 1 — 1 1 560.2 1 1 — 1 1 [ 58 58 ] 1 1 Na 2 SiF 6 1 1 365; 468 1 1 629 1 1 0.37 1 1 — 1 1 3.8 1 1 1.017 1 1 — 1 1 — 1 1 [ 59 59 ] 1 1 (NH 4 ) 3 SiF 7 1 1 360; 460 1 1 630 1 1 — 1 1 340 1 1 — 1 1 — 1 1 — 1 1 66.8 1 1 [ 32 32 ] 1 1 K 2 TiF 6 1 1 362; 468 1 1 632 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 85.33 1 1 [ 60 60 ] 1 1 Na 2 TiF 6 1 1 377; 476 1 1 620 1 1 — 1 1 — 1 1 4.163 1 1 1.037 1 1 504.7 1 1 — 1 1 [ 61 61 ] 1 1 Rb 2 TiF 6 1 1 362; 468 1 1 630 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 91 1 1 [ 62 62 ] 1 1 Cs 2 TiF 6 1 1 360; 466 1 1 629 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 98.7 1 1 [ 49 49 ] 1 1 BaTiF 6 1 1 366; 467 1 1 636 1 1 0.940 1 1 425 1 1 3.44 1 1 — 1 1 610 1 1 75 1 1 [ 63 63 ] 1 1 Na 3 HTiF 8 1 1 350; 460 1 1 627 1 1 — 1 1 — 1 1 3.55 1 1 — 1 1 644.63 1 1 84.2 1 1 [ 40 40 ] 1 1 Na 2 GeF 6 1 1 358; 470 1 1 628 1 1 — 1 1 — 1 1 3.4 1 1 1.016 1 1 626 1 1 — 1 1 [ 64 64 ] 1 1 K 2 GeF 6 1 1 365; 470 1 1 634 1 1 1.64 1 1 — 1 1 — 1 1 — 1 1 — 1 1 94 1 1 [ 65 65 ] 1 1 BaGeF 6 1 1 360; 470 1 1 635 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 66 66 ] 1 1 KRbGeF 6 1 1 370; 467 1 1 620 1 1 0.918 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 67 67 ] 1 1 CsNaGeF 6 1 1 360; 470 1 1 630 1 1 — 1 1 443 1 1 — 1 1 1.03 1 1 600 1 1 95.6 1 1 [ 68 68 ] 1 1 Li 2 ZrF 6 1 1 376; 463 1 1 631 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 69 69 ] 1 1 Na 3 AlF 6 1 1 360; 468 1 1 630 1 1 — 1 1 — 1 1 3.6 1 1 1.013 1 1 598 1 1 — 1 1 [ 70 70 ] 1 1 K 3 AlF 6 1 1 360; 468 1 1 630 1 1 — 1 1 — 1 1 3.19 1 1 1.02 1 1 672 1 1 — 1 1 [ 71 71 ] 1 1 Rb 3 AlF 6 1 1 360; 467 1 1 627 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 81 1 1 [ 72 72 ] 1 1 Cs 3 AlF 6 1 1 361; 467 1 1 634 1 1 0.286 1 1 — 1 1 — 1 1 — 1 1 — 1 1 48.2 1 1 [ 73 73 ] 1 1 (NH 4 ) 3 AlF 6 1 1 365; 468 1 1 630 1 1 — 1 1 368 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 74 74 ] 1 1 K 2 LiAlF 6 1 1 360; 460 1 1 636 1 1 — 1 1 — 1 1 3.9 1 1 1.004 1 1 557 1 1 — 1 1 [ 75 75 ] 1 1 Cs 2 NaAl 3 F 12 1 1 356; 465 1 1 633 1 1 0.295 1 1 — 1 1 3.6 1 1 1.013 1 1 598 1 1 — 1 1 [ 76 76 ] 1 1 Rb 2 NaAlF 6 1 1 357; 465 1 1 634 1 1 — 1 1 433 1 1 — 1 1 — 1 1 — 1 1 59.2 1 1 [ 49 49 ] 1 1 NaRbSnF 6 1 1 365; 467 1 1 621 1 1 0.405 9 1 1 — 1 1 — 1 1 — 1 1 — 1 1 59.4 1 1 [ 77 77 ] 1 1 Li 3 GaF 6 1 1 360; 460 1 1 633 1 1 0.29 1 1 348 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 78 78 ] 1 1 LiSrGaF 6 1 1 378; 467 1 1 628 1 1 0.202 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 79 79 ] 1 1 Na 3 GaF 6 1 1 358; 465 1 1 625 1 1 — 1 1 — 1 1 3.58 1 1 — 1 1 599.8 1 1 — 1 1 [ 80 80 ] 1 1 Rb 2 KGaF 6 1 1 358; 462 1 1 628 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 81 81 ] 1 1 K 2 NaScF 6 1 1 360; 468 1 1 630 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 70.3 1 1 [ 37 37 ] 1 1 K 3 ScF 6 1 1 367; 470 1 1 631 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 67.18 1 1 [ 82 82 ] 1 1 Cs 2 NaScF 6 1 1 365; 470 1 1 633 1 1 — 1 1 340 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 51 51 ] 1 1 Cs 2 KScF 6 1 1 365; 470 1 1 629 1 1 — 1 1 325 1 1 — 1 1 — 1 1 — 1 1 58.8 1 1 [ 51 51 ] 1 1 Cs 2 RbScF 6 1 1 365; 470 1 1 628.5 1 1 — 1 1 385 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 51 51 ] 1 1 Cs 3 ScF 6 1 1 365; 470 1 1 628.5 1 1 — 1 1 315 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 51 51 ] 1 1 (NH 4 ) 2 NaScF 6 1 1 367; 474 1 1 630 1 1 — 1 1 360 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 83 83 ] 1 1 K 2 LiInF 6 1 1 360; 465 1 1 630 1 1 0.37 1 1 470 1 1 — 1 1 — 1 1 550 1 1 — 1 1 [ 84 84 ] 1 1 K 2 NbF 7 1 1 369; 467 1 1 628 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 71.3 1 1 [ 85 85 ] 1 1 K 3 RbGe 2 F 12 1 1 360; 467 1 1 630 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 86 86 ] 1 1 Na 3 Li 3 Sc 2 F 12 1 1 355; 461 1 1 627 1 1 0.59 1 1 413 1 1 3.59 1 1 1.03 1 1 604 1 1 66.8 1 1 [ 55 55 ] 1 1 Ba 3 Sc 2 F 12 1 1 367; 467 1 1 629 1 1 0.570 1 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 41 41 ] 1 1 KNaNbF 7 1 1 360; 475 1 1 627 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 87 87 ] 1 1 KZnF 3 1 1 358; 469 1 1 636 1 1 — 1 1 — 1 1 3.4 1 1 — 1 1 621 1 1 — 1 1 [ 35 35 ] 1 1 Cs 2 MoO 2 F 3 1 1 371;468 1 1 633 1 1 — 1 1 >473 1 1 — 1 1 — 1 1 — 1 1 54 1 1 [ 88 88 ] 1 1 Na 2 WO 2 F 4 1 1 367;469 1 1 619 1 1 0.49 1 1 340 1 1 3.9 1 1 1.036 4 1 1 546 1 1 76.64 1 1 [ 89 89 ] 1 1 Cs 2 WO 2 F 4 1 1 374;470 1 1 632 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 90 90 ] 1 1 BaTiOF 4 1 1 360;464 1 1 632 1 1 — 1 1 — 1 1 3.7 1 1 — 1 1 577 1 1 — 1 1 [ 91 91 ] 1 1 Cs 2 NbOF 5 1 1 371;474 1 1 632 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 63.4, 21.2 * 1 1 [ 92 92 ] 1 1 BaNbOF 5 1 1 390;480 1 1 629 1 1 0.506 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 93 93 ] 4　Mn 4+ 激活的铝酸盐荧光粉 1 铝酸盐是最常见的Mn 4+ 掺杂氧化物基质，［AlO 6 ］八面体的Al 3+ ( r =0.068 nm)与Mn 4+ 半径相近。常见的铝酸盐基质包括石榴石型、钙钛矿型、类磁铁铅矿型等。绝大多数铝酸盐以氧化铝、碳酸盐和其他氧化物为原料，通过高温固相法来制备，但产物的微观形貌较难控制。以溶胶-凝胶法为代表的湿化学合成法制备的铝酸盐荧光粉具有形貌规则、粒径均匀的优点 [ 94 94 - 95 95 94-95 ] 。Mn 4+ 激活的铝酸盐荧光粉以CaAl 12 O 19 ∶Mn 4+ (CAOM) 为典型代表。CAO的XRD图谱如 图3(a) 图3(a) 所示，属于六方结构的类磁铁铅矿型，最早由Bergstein报道，空间群 P 63/ mmc ，晶格参数 a =0.556 nm, c =2.189 nm [ 96 96 ] 。高温固相法制备的CAOM扫描电镜照片如 图3(b) 图3(b) 所示，其形状是带有棱角的多边形，且随着温度升高，多边形结构进一步形成，晶粒尺寸增大 [ 96 96 ] 。在CAO的晶胞中存在1个12配位Ca 2+ 位点、1个［AlO 4 ］四面体位点、1个［AlO 5 ］三角双锥体位点和3个不同的［AlO 6 ］八面体位点，并且Al 3+ 和O 2- 结合在一起( 图3(c) 图3(c) ) [ 97 97 ] 。Mn 4+ 取代CAO基质中的Al 3+ 位置后，增加荧光粉的结构不均匀性和化学复杂性。CAOM的荧光光谱( 图3(d) 图3(d) )在600~700 nm之间是较窄的发射带，分别在643,656,666,671 nm处出现了4个尖锐的峰；在250~550 nm之间是宽频带，分别在338,398,468 nm处有3个峰 [ 98 98 ] 。由于CAOM具有适当的带隙和较大的Stokes位移，因此其激发光谱与YAG∶Ce的发射光谱重叠很小。鉴于此，Liu等 [ 99 99 ] 将蓝光InGaN芯片与YAG∶Ce黄粉、CAOM红粉制作成白光LED器件( 图3(e) 图3(e) )，测得器件的流明效率为63 lm/W，色温4 553 K，显色指数达到88.5。 图3(f) 图3(f) 表明器件的色坐标也位于暖白光区域 [ 99 99 ] 。然而，由于Al 3+ 与Mn 4+ 价态不同，需要添加其他离子来保持荧光粉的整体电荷平衡，最常用的是M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211007&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211011&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211009&type= 。在保证结构基本不变和电荷平衡条件下，通过成分修饰，例如Mn 4+ 与Ge 4+ 、Cl - 、K + 、Zn 2+ 、Bi 3+ 共掺 [ 104 104 - 108 108 104-108 ] ,Ga 3+ 取代A http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211014&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211017&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211015&type= 或Y 3+ -Mg 2+ 共取代Ca 2+ -A http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211019&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211025&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211022&type= 等，CAO∶Mn 4+ 荧光粉的发光强度和热稳定性可得到有效提高。 表2 表2 列举了近来报道的Mn 4+ 激活铝酸盐荧光粉，比较典型的是Sr 2 MgAl 22 O 36 、CaAl 4 O 7 、 SrAl 2 O 4 、CaAl 2 O 4 、CaYAlO 4 和SrMgAl 10 O 17 等基质，总结它们的光谱学性能可知其最强激发峰在300~360 nm，与近紫外LED芯片匹配。不同铝酸盐基质的共价性也有差异，导致发射峰的位置变化较大，变化规律不明显。经过组分调控后，部分铝酸盐荧光粉的量子效率能够接近90%，但总体比氟化物荧光粉低。综上所述，Mn 4+ 激活铝酸盐荧光粉具有如下优点:(1) 制备工艺简单，过程无污染；(2)化学稳定性好。铝酸盐荧光粉在湿度环境不易水解，而氟化物荧光粉湿化学稳定性较差。但是，铝酸盐荧光粉也存在缺点，制约了其商业化:(1)大部分铝酸盐荧光粉的发射峰位于人眼敏感区域外(超过650 nm)，接近于深红色区域，不适用于暖白光照明场景，但有可能在辅助植物生长领域得到应用 [ 97 97 ] ;(2)发射峰的半峰宽比Mn 4+ 激活的氟化物荧光粉宽，能量分散，发光效率较低。 注： M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211047&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211053&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211050&type= 的发射波长是指M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211054&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211059&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211056&type= 发射强度最大值对应的波长，所有的数据都对应着一定浓度的M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211061&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211066&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211063&type= ，不同浓度的M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211069&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211073&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211070&type= 的发射强度不同。—表示无参考数据； * 指外量子效率，不加符号表示内量子效率。 1 1 Host 1 1 λ ex /nm 1 1 λ em /nm 1 1 Δ E /eV　 1 1 T 1/2 /K　 1 1 Dq / B 　 1 1 β 1 　 1 1 B /cm -1 　 1 1 QE/% 1 1 Reference 1 1 LaAlO 3 1 1 356; 490 1 1 732 1 1 — 1 1 — 1 1 — 1 1 0.96 1 1 921 1 1 89.3 1 1 [ 110 110 ] 1 1 CaYAlO 4 1 1 358; 473 1 1 713 1 1 0.998 8 1 1 420 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 111 111 ] 1 1 GdAlO 3 1 1 360; 483 1 1 698 1 1 0.373 1 1 469.5 1 1 2.84 1 1 — 1 1 721.9 1 1 24 1 1 [ 112 112 ] 1 1 CaGdAlO 4 1 1 338; 500 1 1 712 1 1 0.433 1 1 — 1 1 1.92 1 1 — 1 1 1037 1 1 61 1 1 [ 102 102 ] 1 1 BeAl 2 O 4 1 1 275; 418 1 1 683 1 1 0.285 2 1 1 385 1 1 1.68 1 1 — 1 1 1423 1 1 — 1 1 [ 113 113 ] 1 1 MgAl 2 O 4 1 1 340; 470 1 1 656 1 1 0.781 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 114 114 ] 1 1 ZnAl 2 O 4 1 1 320; 465 1 1 679 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 27.3 1 1 [ 115 115 ] 1 1 Al 2 O 3 1 1 320; 480 1 1 678 1 1 0.52 1 1 — 1 1 1.74 1 1 1.15 1 1 1 202.3 1 1 — 1 1 [ 116 116 ] 1 1 Ca 3 Al 4 ZnO 10 1 1 348; 466 1 1 714 1 1 0.245 1 1 423 1 1 — 1 1 — 1 1 — 1 1 60 1 1 [ 117 117 ] 1 1 Lu 3 Al 5 O 12 1 1 326; 466 1 1 670 1 1 — 1 1 — 1 1 — 1 1 — 1 1 789 1 1 72.41 1 1 [ 100 100 ] 1 1 Y 3 Al 5 O 12 1 1 345; 480 1 1 673 1 1 0.317 1 1 — 1 1 — 1 1 — 1 1 — 1 1 42 1 1 [ 103 103 ] 1 1 Sr 2 Al 6 O 11 1 1 305; 450 1 1 652 1 1 — 1 1 398 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 118 118 ] 1 1 SrMgAl 10 O 17 1 1 320; 467 1 1 662 1 1 — 1 1 — 1 1 2.22 1 1 1.05 1 1 951 1 1 51.4 1 1 [ 119 119 ] 1 1 BaZn 1.06 Al 9.94 O 17 1 1 295; 450 1 1 665 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 120 120 ] 1 1 BaMgAl 10 O 17 1 1 335; 465 1 1 660 1 1 0.293 1 1 — 1 1 2.57 1 1 0.98 1 1 828 1 1 — 1 1 [ 121 121 ] 1 1 Ca 14 Al 10.25 Zn 6 O 35 1 1 350; 470 1 1 715 1 1 0.235 4 1 1 455 1 1 — 1 1 — 1 1 — 1 1 90.0 1 1 [ 122 122 ] 1 1 LaMgAl 11 O 19 1 1 330; 470 1 1 663 1 1 0.38 1 1 — 1 1 — 1 1 — 1 1 — 1 1 38.5 1 1 [ 97 97 ] 1 1 CaAl 12 O 19 1 1 320; 462 1 1 658 1 1 — 1 1 — 1 1 2.13 1 1 — 1 1 1 011.9 1 1 — 1 1 [ 123 123 ] 1 1 CaAl 12 O 19 1 1 342; 465 1 1 655 1 1 0.46 1 1 — 1 1 — 1 1 — 1 1 — 1 1 82.1 1 1 [ 109 109 ] 1 1 SrAl 12 O 19 1 1 341; 473 1 1 659 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 [ 124 124 ] 1 1 Sr 4 Al 14 O 25 1 1 359; 461 1 1 655 1 1 0.74 1 1 — 1 1 3.8 1 1 — 1 1 570.17 1 1 — 1 1 [ 125 125 ] 1 1 CaMg 2 Al 16 O 27 1 1 345; 468 1 1 655 1 1 — 1 1 — 1 1 6.70 1 1 — 1 1 321 1 1 35.6 1 1 [ 126 126 ] 1 1 Ca 14 Zn 6 AlO 35 1 1 289; 452 1 1 714 1 1 — 1 1 — 1 1 — 1 1 — 1 1 — 1 1 83 1 1 [ 127 127 ] 5　优化光谱学性能 1 由于3d 3 电子与晶格振动间强耦合，Mn 4+ 的光谱性质与基质的晶体场强度、共价性和格位对称性密切相关 [ 103 103 ] 。而零声子线的发射强度由Mn 4+ 所处的局部晶体场环境对称性决定，即Mn 4+ 占据的八面体环境发生对称畸变会使ZPL发射增强 [ 36 36 ] 。近来，文献中优化光谱学性能的策略可归纳为4种:(1)破坏八面体格位对称性，增强ZPL发射；(2)格位电荷平衡，减小非辐射跃迁；(3)改善浓度猝灭；(4)引入敏化剂离子，设计能量传递路径。 5.1　增强ZPL发射 2 近邻格位被不同于原组分的阳离子取代后，Mn 4+ 所处的八面体产生拉长或压缩等晶格畸变，格位对称性被破坏，奇对称场产生，Mn 4+ 的d-d跃迁禁阻被打破，ZPL发射由此增强。格位取代一般发生在基质晶格阳离子位点，如碱金属、碱土金属、稀土离子、离子复合物的中心阳离子等 [ 128 128 ] 。SrMgAl 10- y Ga y O 17 ∶Mn 4+ 荧光粉中，由于发光中心逐渐由Al 3+ 格位转变为Ga 3+ 格位，发光强度逐渐提高，SrMgAl 7 Ga 3 O 17 ∶Mn 4+ 的发光强度提高至未掺杂的1.63倍，如 图4(a) 图4(a) 所示 [ 119 119 ] 。该取代过程属于同价格位取代，不会产生多余电荷，类似的思路，有研究人员用Al 3+ 替代Ga 3+ 得到了Gd 3 Ga 5- x-δ Al x- y+δ O 12 ∶ y Mn 4+ 固溶体， x =3时得到的荧光粉发射强度提高了6.8倍，如 图4(b) 图4(b) 所示 [ 129 129 ] 。Fang等 [ 40 40 ] 采用共沉淀法制备含氢的Na 3 HTi 1- x Mn x F 8 ，由于H的引入在结构中增加了额外的键，导致［TiF 6 ］ 2- 八面体单元产生畸变。考虑到H—F键强度高，进一步使得［TiF 6 ］ 2- 变形，结果内量子效率最高达到89.5%,Mn 4+ 的ZPL发射增强。然而，在某些氟化物基质中，破坏格位对称性不一定能提高发光强度，还会受其他因素的影响。Dong等 [ 41 41 ] 研究发现，Ba 3 Sc 2 F 12 ∶Mn 4+ 的Ba 2+ 逐步被Ca 2+ 取代后发射强度会减小，这可能是由于Ba 2+ 较大的离子半径和较弱的离子极化导致基质晶格共价性更强，有利于Mn 4+ 高效发光( 图4(c) 图4(c) ) 。 5.2　格位电荷平衡 2 由于在铝酸盐、锑酸盐、铌酸盐等基质中，Mn 4+ 与所占据格位的离子价态不一定相同，因此需要添加其他离子来保持荧光粉的电荷平衡，以此来减小非辐射跃迁，最常用的是Mg 2+ 、Na + 、K + 等。Chen等 [ 103 103 ] 通过研究YAG∶ M /Mn 4+ ( M =Li + ,Na + ,Mg 2+ ,Ca 2+ ,Ge 4+ ,Ti 4+ )，发现Mg 2+ 能更加显著地提高Mn 4+ 的发光强度，如 图5(a) 图5(a) 所示。他们认为Mg 2+ 离子不仅可以作为电荷补偿中心，而且可以抑制相邻Mn 4+ 离子之间的能量迁移，是提高Mn 4+ 发光性能的最有效的掺杂剂 ( 图5(b) 图5(b) ) 。Ge 4+ 仅能抑制Mn 4+ 离子之间的能量迁移，Ca 2+ 仅能作为电荷补偿离子来平衡整体电荷，故与Mg 2+ 相比，Ge 4+ 和Ca 2+ 对Mn 4+ 发光的增强效果相对较低。Zhong等 [ 130 130 ] 用Ge 4+ - M + ( M =Li,Na,K)共取代Ca 14 Ga 10 Zn 6 O 35 ∶Mn 4+ 的Ca 2+ -Ga 3+ ，减小了无辐射跃迁，发射强度分别提高至未掺杂情况下的169.4%、195.0% 和198.9%，最高的内量子效率达到50.9%。Zheng等 [ 97 97 ] 采用Y 3+ - Mg 2+ 共取代Ca 2+ -Al 3+ 的策略制备出Ca 1- x Y x Al 12- x Mg x O 19 ∶Mn 4+ 荧光粉，当 x 从0增加到0.1时，量子效率从未掺杂的52%提高到56%，荧光粉的发光强度相应提高。 5.3　改善浓度猝灭 2 较高的浓度能保证Mn 4+ 在紫外或蓝光区域的充分吸收，有利于获得高外量子效率 [ 50 50 , 131 131 ] 。然而，高浓度掺杂时，Mn 4+ 离子间的能量迁移产生浓度猝灭。“浓度猝灭”是指Mn 4+ 掺杂量增多而荧光粉发射强度减小的现象，其原因是Mn 4+ 间的能量迁移过程中，能量传递到了猝灭中心(缺陷和杂质离子)，发生无辐射跃迁，如 图6(a) 图6(a) 所示。猝灭的临界半径 R c 可通过下式估算 [ 132 132 ] : http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211108&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211111&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211113&type= 其中， V 是晶胞体积， C 为临界浓度， N 为掺杂离子在晶胞内所能占据的位点数。理论上，减小Mn 4+ 间的能量迁移能够改善浓度猝灭，提高有效掺杂浓度，进而提高发光强度和量子效率。 Zhong等在Ca 14 Al 10 Zn 6 O 35 中引入过量Al，结果显示随着Al含量的逐渐增加，Ca 14 Al x Zn 6 O 35 ∶Mn 4+ 的量子效率从83.9%提高到90.0%，如 图6(b) 图6(b) 所示 [ 122 122 ] 。他们认为可能是过量的Al原子形成了额外的［AlO 6 ］八面体，从而容纳了更多有效的Mn 4+ 。Senden [ 131 131 ] 在研究K 2 TiF 6 ∶Mn 4+ 的浓度猝灭现象时发现，高浓度掺杂下能量直接从Mn 4+ 离子转移到猝灭中心，而非通过Mn 4+ -Mn 4+ 间的能量迁移。Chen等发现，尽管其他离子与Mn 4+ 共掺杂不能使得Mn 4+ 最优浓度增加，但共掺后的发射强度远高于相应的单掺杂样品 [ 103 103 ] 。这可能是由于共掺离子未能均匀地占据Mn 4+ 的近邻格位，难以有效减小Mn 4+ 之间的能量传递。 5.4　引入敏化剂 2 利用Mn 4+ 和其他离子间的能量传递，设计能量传递路径也能提高特定波长激发的发光强度。例如，Huang等 [ 133 133 ] 基于阳离子的半径和配位性，通过高温固相反应在双钙钛矿结构的Ba 2 GdNbO 6 中以Bi 3+ /Mn 4+ 取代Gd 3+ /Nb 5+ 阳离子，利用Bi 3+ 的发射光谱和Mn 4+ 的激发光谱重叠的特性，设计了Bi 3+ →Mn 4+ 的能量传递途径。在315 nm紫外激发下，Ba 2 GdNbO 6 ∶Bi 3+ ,Mn 4+ 荧光粉分别在Bi 3+ 的464 nm和Mn 4+ 的689 nm处出现了两个发射波段，并且Bi 3+ →Mn 4+ 的最高能量传递效率为93.21% ( 图7(a) 图7(a) )。Wei等 [ 134 134 ] 在Mg 3 Y 2(1- y ) Ge 3 O 12 ∶Mn 4+ 中通过共掺杂Eu 3+ ，发现共掺杂后的荧光粉在298~523 K温度范围内发光强度不断增强，其中Mg 3 Eu 2 Ge 3 O 12 ∶Mn 4+ 样品在523 K时的强度达到298 K时的120%( 图7(b) 图7(b) ) 。在393 nm的室温激发下，内量子产额从15.1%明显提高到76.5%，说明能量传递对增强Mn 4+ 发光起作用。 6　改善热猝灭性能和湿化学稳定性 1 6.1　改善热猝灭性能 2 荧光粉的热稳定性必须满足两个要求:(1) 在150 ℃下的损失不得超过其量子产率的10%;(2)能够在各种工作温度下保持颜色质量 [ 135 135 ] 。Mn 4+ 掺杂的红色荧光粉在较高温度下的发射强度会急剧下降，这种热猝灭产生的原因存在不同说法。Paulusz [ 26 26 ] 提出Mn 4+ 激活的氟化物的热猝灭是由于 2 E的电子热激发到 4 T 2 ，之后直接无辐射跃迁到 4 A 2 基态；而Blasse [ 19 19 ] 与Dorenbos [ 136 136 ] 则认为热猝灭与电荷转移态和 4 A 2 基态相交有关。 图8(a)、(b) 图8(a)、(b) 分别是说明不同热猝灭机制示意图，大多数研究人员倾向于Paulusz的解释，认为提高晶体场中Mn 4+ 的 4 T 2 能级会提高Mn 4+ 的热猝灭温度。Senden等 [ 131 131 ] 通过测量K 2 TiF 6 ∶Mn 4+ 在4~600 K之间的发光光谱、衰减曲线，并比较其他Mn 4+ 掺杂氟化物荧光粉和氧化物荧光粉对温度的依赖，发现随着 4 T 2 能量的提高，猝灭温度 T 1/2 相应升高，这表明猝灭是通过 4 T 2 激发态和 4 A 2 基态之间的热激活交叉产生的，如 图8(c) 图8(c) 所示。调节Mn 4+ 所处格位的晶体场强度可以提高 4 T 2 能级，进而抑制 4 T 2 和 4 A 2 间可能发生的无辐射跃迁过程。当晶体场强度增大、能级劈裂加大时， 2 E与 4 T 2 能级间能量差增大，电子无法热激发越过能垒Δ E ，热猝灭性能就会改善。通过Arrhenius方程能够估算激活能Δ E : http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211138&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211142&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211145&type= 其中， I 0 是室温或零摄氏度下荧光粉的初始发射强度， I T 是不同温度下的发射强度， c 是常数， κ 是Boltzman常数。 Gai等 [ 137 137 ] 采取Y 3+ 替换La 3+ 制备了L http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211147&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211152&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211149&type= -Y x MgTiO 6 ∶Mn 4+ 荧光粉，其在 x > 1.2时获得高热稳定性， x =1.95时的发光强度在150 ℃达到室温下的83.5%，相比较之下，未掺杂荧光粉在同样温度下只能达到室温下的56.9%( 图8(d) 图8(d) ) 。他们给出的解释是:开始掺入量较小，［Mg/TiO 6 ］会膨胀，Mn—O键变长，晶体场强度减小， 4 T 2 能级降低，无辐射跃迁几率增大；随着掺入量增多，晶格整体呈收缩趋势， 4 T 2 能级又会被拉高，热稳定性因此增强，如 图8(e) 图8(e) 所示。Lang等 [ 65 65 ] 用共沉淀法制备了K 2 (Ge 1- x Si x )F 6 ∶Mn 4+ (KGSFM)，当 x =0.3时，423 K的KGSFM发射强度较同温度未掺杂的K 2 GeF 6 ∶Mn 4+ 增加14%，较室温下同组分增加17%，如 图8(f) 图8(f) 所示。原因是Si的引入导致晶胞收缩，Mn—F键缩短，增强了Mn 4+ 形成的化学键刚性。KGSFM( x =0,0.2,0.3)的激活能分别为1.31,1.37,1.64 eV，与氮化物红色荧光粉(~0.25 eV) 相比有了很大提升。综上所述，通过格位取代来压缩Mn 4+ 所处的八面体，使Mn—O/F键长减小，晶体场劈裂增大，能垒Δ E 增大，能够改善热猝灭性能。 6.2　提高湿化学稳定性 2 由于 ［MnF 6 ］ 2- 基团的表面水解，氟化物荧光粉抗湿性较差，造成相应的WLED在长期工作中性能劣化，限制了该类材料在潮湿环境中的商业应用 [ 17 17 ] 。Chen等 [ 100 100 ] 研究了Lu 3 Al 5 O 12 (简写为LAG)∶Mn 4+ ,Mg 2+ 与K 2 TiF 6 ∶Mn 4+ 的抗湿性随时间的变化，结果如 图9(a)、(b) 图9(a)、(b) 所示。2 h后，Lu 3 Al 5 O 12 ∶Mn 4+ ,Mg 2+ 的发射强度仍能保持初始值的92.63%，而K 2 TiF 6 ∶Mn 4+ 仅保持0.04%。这表明，铝酸盐荧光粉的抗湿性较好，在湿度环境中发射强度衰减小。因此，如何提高氟化物荧光粉的湿化学稳定性很关键，目前主要有三种策略:(1)表面包覆或表面钝化:用相同结构的氟化物作为壳层来保护M http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211155&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211163&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211160&type= 或在表面包覆一些绝缘层，减少活性离子或基团的暴露。常用的包覆绝缘层有疏水烷基磷酸、十八烷基三甲氧基硅烷、扁桃酸、油酸、Ca http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211167&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211175&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21211171&type= 、Al 2 O 3 、TiO 2 和纳米尺寸的碳层等 [ 140 140 ] 。(2)掺杂 [ 63 63 ] ，改变荧光粉固有的性质。(3)制备出氟化物荧光粉单晶，依据是与多晶粉末相比，单晶明显提高了量子效率、耐湿性和热稳定性 [ 49 49 - 50 50 49-50 ] 。 Yu等 [ 140 140 ] 用H 2 C 2 O 4 溶液处理K 2 GeF 6 ∶Mn 4+ (KGF)，构造含Mn 4+ 极少的壳层结构，即K 2 Ge 1- x Mn x F 6 @K 2 GeF 6 。由于在处理KGF颗粒表面固液平衡过程中，在荧光粉核上原位沉积了含Mn 4+ 极少的表面壳层，因此发光中心不会与外界湿度环境接触。经过处理的KGF荧光粉(T-KGF)具有优异的耐水性能，随着浸水时间延长，发光强度相对于初始值几乎保持不变 ( 图9(c) 图9(c) )。Dong等 [ 60 60 ] 用KF和Ca(NO 3 ) 2 制备了CaF 2 溶液，与已经制备好的K 2 TiF 6 ∶Mn 4+ (KTFM)荧光粉混合，得到KTF@CaF 2 。包覆后的KTFM发光强度高于KTF，且CaF 2 形成的保护层使得荧光粉的耐湿性也得到了提高。 图9(d) 图9(d) 所示的耐湿性测试中KTF@CaF 2 的发光强度仅下降了13.6%，而KTF的发光强度下降了93.2%。Hong等 [ 66 66 ] 把BaGeF 6 ∶Mn 4+ 包覆聚丙二醇 (PPG) 和NaGdF 4 ∶Dy 3+ 纳米颗粒，前者能改善荧光粉的表面缺陷和提高其抗湿性，发光强度增加11%，如 图9(e) 图9(e) 所示。 图9(f) 图9(f) 中，包覆聚丙二醇的BaGeF 6 ∶Mn 4+ 在水中浸泡到120 h的外观无明显变化，而未包覆的对照组外观已经呈暗黑色 [ 66 66 ] 。Zhou等 [ 49 49 ] 采用简便的溶剂交换法制备了Cs 2 TiF 6 ∶Mn 4+ (CTFM)单晶，在高湿度 (85%) 和较高温度 (85 ℃) 的环境中，CTFM多晶粉末的黄色在6 h后迅速转变为棕色，而CTFM单晶粉末在48 h后仍保持黄色，PL强度与初始值相比几乎保持在100%，对照的商业KSFM粉末的PL强度则低至初始值的30%。而在仅6 h后，CTFM多晶粉末的PL强度迅速下降到初始值的10%左右。这些结果清楚地表明CTFM单晶的抗湿性能有了显著的改善 [ 49 49 ] 。 7　总结与展望 1 Mn 4+ 激活的红色荧光粉以其宽带吸收、窄带发射、色纯度高以及成本低的优点，在白光LED室内照明、农业上辅助植物生长、背光显示等领域具有重要应用前景。本文综述了Mn 4+ 激活的典型LED红色荧光粉研究进展，主要总结了各种Mn 4+ 激活的氟化物和铝酸盐荧光粉的光谱学性能，以及从机理上优化光谱学性能、改善热猝灭性能和化学稳定性的最新进展。目前，Mn 4+ 激活的典型LED红色荧光粉的结构调控、性能突破和实用化依然面临着挑战: (1) 对于Mn 4+ 激活的氟化物荧光粉，首先其抗湿性较差，在表面包覆相同结构的氟化物壳层或绝缘层来保护内部Mn 4+ 发光中心以及制备荧光粉单晶，都能有效提高湿化学稳定性；其次，它的外量子效率较低，通过格位(共)取代降低Mn 4+ 所处局域晶体场的对称性，可提高跃迁几率，进而提高外量子效率。优化合成方法和减少基质缺陷来减小浓度猝灭，提高有效掺杂浓度，使之尽可能接近理论的最佳掺杂浓度，也可以提高外量子效率。此外，其制备过程易对环境产生污染，虽然少数文献提及可以采用低毒原料制备氟化物荧光粉，但未得到推广，故研究出不使用HF合成Mn 4+ 掺杂氟化物红色荧光粉且具有普遍适用性的方法很有意义。 (2)对于Mn 4+ 激活的铝酸盐荧光粉，首先，其内量子效率较低，通过平衡电荷、减小非辐射跃迁、改善浓度猝灭、引入敏化剂离子等策略均能提高发光强度和内量子效率。其次，它的发光波段超过了人眼感受的敏感限度，在蓝光波段激发弱。在同时兼顾效率的基础上，通过掺杂降低基质共价性，以此促进波长从深红色到橙色/红色的蓝移和增强蓝光区域的吸收，有待继续研究。 总之，对于Mn 4+ 激活的红色荧光粉，继续探索新型掺杂基质，通过格位(共)取代和优化合成方法等策略，制备出强烈吸收蓝光、有效发射带在610~630 nm之间、量子产率高、在温度和湿度苛刻的环境下能保持化学和热稳定性的荧光粉，是非常必要的。 本文专家审稿意见及作者回复内容的下载地址:http://cjl.lightpublishing.cn/thesisDetails#10.37188/CJL.20210148. 参考文献: SCHUBERT E F , KIM J K . 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