上转换和量子剪裁

上转换和量子剪裁上转换和量子剪裁上转换发光通常，PL发射波长比激发波长要长，说明过程中有能量损失，以热能的形式损耗上转换(upconversion)发光：长波吸收，然后发出短波光的现象上转换材料过程不同于斯托克斯规那么及瓦维洛夫定律所涉及的过程属反斯托克斯现象上转换发光的效率随着激发光强的增加而超线性地增长，所以，在激光的高密度激发下就容易观察到最简单的上转换现象发生在同一个或同一种发光中心上，它的发光过程分为三类1〕一个中心同时吸收两个光子然后发射一个大光子的叠加过程Ø此类中心可以同时吸收两个光子而到达激发态激发态和基态之间并没有中间的激发态，是一种双光子吸收过程Ø双光子吸收中的两个光子可以有不同的能量，即不同的频率但它们的能量之和要等于中心到达激发态时所需要的能量，即：h1+h2 = E2E1Ø 连续改变1，保持2恒定，当发生吸收时即可得到E2E1的数值ØCaF2:Eu2+，在红宝石激光器的6943 Å谱线的强激发下，发射一个4250 Å光子而此材料在6943 Å附近是透明的，不能吸收6943 Å的光h1h22) 激发态吸收被光激发到激发态上的电子再吸收光子跃迁到更高能级。

a)(a)发射光发射光(3)(3)光子能量小于激发光光子能量，通过与晶格光子能量小于激发光光子能量，通过与晶格的作用，有一局部能量转变成热能；的作用，有一局部能量转变成热能； (b) (b)上转换材料吸收上转换材料吸收激发光中的多个光子激发光中的多个光子(1-1(1-1和和1-21-2两个两个) )发射一个光子，发射发射一个光子，发射光子的能量大于激发光子的能量光子的能量大于激发光子的能量2) 激发态吸收LaF3中Tm3+的能级和647.1nm激发下的上转换过程氟F(Z = 9)，镧La (Z = 57)， 铥Tm(Z = 69)一、多光子吸收(红色)：(1)3H63F2；(2)3H4 1D2；3F4 1G4；(3)1G4 3P1二、驰豫(绿色) ：3F2 ➟3H4(3F2、3F3和3F4相距很近，电子很快驰豫到3H4)；3P1➟ 1I6三、辐射(黑色) ：(1)驰豫到3H4的电子—3H4 3H6、3F4(IR)； (2)蓝光：1G4 3H6—480nm；1D2 3F4—450nm；(3)紫外：1D2 3H6—360nm；1I63F4—340nm激发态吸收中的吸收雪崩现象：基态吸收弱，激发态吸收强。

1、基态吸收较弱，开始时激发态E1上的电子不多，尽管激发态吸收强，到达E2上的电子也不多，上转换发光较弱2、 E1上电子数减少1个(激发态吸收)：E1 E23、交叉驰豫—E2 E1G E1 (无基态吸收) ， E1能级上电子数倍增， 吸收激发光从E1 E2的电子数也倍增，上转换增强1)激发态E1上的电子数增多； (2)基态G上的电子数减少；(3)E1上的电子经由激发态吸收，而非基态吸收弱吸收强吸收h2h13) 逐次能量传递Yb3+，Tm3+双掺杂体系/镱Yb (Z = 70)激发：960nm(IR)；发射：蓝光三步能量传递(1) Yb3+(2F5/22F2/7)➩Tm3+(3H6 3H5 ➟3F4)；(2) Yb3+(2F5/22F2/7)➩Tm3+(3F4 3F2,3 ➟3H4)；(3) Yb3+(2F5/22F2/7)➩Tm3+(3H4 1G4)处于激发态的同种离子之间的能量传递也能产生上转换发光在高的Tm3+浓度(>1%)样品中，两个激发到3F3的Tm3+间发生交叉驰豫： (3F2,3 3H6) (3F2,3 1D2)3) 逐次能量传递W.F. Silva et al. Highly efficient upconversion emission and luminescence switching from Yb3+/Tm3+ co-doped water-free low silica calcium aluminosilicate glass. J. Lumin. 2021, 128(5-6): 744-746The composition of the sample, in wt%, is (41.5-x-y) of Al2O3, 47.4 of CaO, 7.0 of SiO2, and 4.1 of MgO, with x=0.5 of Tm2O3 and y=2.0 of Yb2O3. low silica calcium aluminosilicate (LSCAS) glass.excitation at 976 nmluminescence switchingThe emissions at 480 and 800 nm of Tm3+ ions are strongly dependent on the excitation intensity, resulting in a switching from 800 to 480 nm emissions with increasing pump intensity. The origin of this switching is the high efficiency of the Yb3+ linear absorption at the excitation energy and the high efficiency of the energy transfer from Yb3+ to Tm3+, resulting, respectively, in saturations of the Yb3+ linear absorption and of the first excited state of Tm3+.Dependence of the upconversion emission intensity ratio r=I(480 nm)/I(800 nm) on the excitation intensity.3) 逐次能量传递Er3+激发: Yb3+➩Er3+(能量传递)/铒Er (Z = 68)(1) Yb3+(2F5/22F7/2)➩Er3+(4I15/24I11/2 ➟ 4I13/2)(2)Er3+(4I11/24F7/2 ➟ 4S3/2)(3)Er3+(4I13/24F9/2)Er3+发射:(1)4S3/24I15/2(550nm)(2)4F9/24I15/2(660nm)上转换材料上转换材料：单掺杂和双掺杂〔一〕掺杂离子单掺杂：利用稀土离子的f-f禁戒跃迁，窄线的振子强度小的光谱限制了对红外光的吸收。

效率低如增加掺杂浓度来增加吸收，那么造成荧光的浓度猝灭为提高红外吸收能力，引入高浓度敏化剂(离子)，采用双掺杂方法上转换材料Ø双掺杂，如：Yb3+，其 2F7/22F5/2的跃迁吸收很强，且波长与950-1000nm的激光匹配良好，而它的激发态又高于激活离子Er3+(4I11/2)、Ho3+(5I6)、Tm3+(3H5)的激发亚稳态，可将吸收的红外光子能量传递给这些激活离子，发生双光子或多光子的加和，从而实现发射短波长的光，上转换过程明显增加因此， Yb3+作为敏化剂是提高上转换效率的重要途径之一Ø激光二极管泵浦源：GaAlAs、AlGaIn和InGaAs，发射波长范围分别与一些稀土离子 (Nd3+、Tm3+、Er3+和Ho3+) 的主吸收带匹配较好上转换材料ØEr3+是一种有效的上转换激活离子，在800-1000nm范围具有丰富的红外光子激发的能级 Er3+在氟化物中的溶解度高， Er3+掺杂的氟化铟、氟锆酸盐和氟磷酸盐是较好的绿光上转换材料Ø影响掺杂的稀土离子发光性能的因素：1.稀土离子-阴离子的相互作用强，上转换发光强度低；2.稀土离子周围对称性低，有利于提高上转换发光强度；3.基质晶格中阳离子的价态高，对上转换发光有利。

上转换材料Ø〔二〕基质材料Ø形态：晶体、玻璃和陶瓷Ø基质材料要求：Ø光学性能好；Ø具有一定的机械强度和化学稳定性；Ø基质材料一般不构成发光能级，但能为激活离子提供适宜的晶体场，使其产生特定的发射；Ø基质材料声子能量小，有利于提高上转换的效率Ø基质材料对激光阈值功率和输出效率也有很大影响上转换材料上转换发光材料种类非常多，根据基质可分为5类：氟化物系列、氧化物系列、氟氧化物系列、卤化物系列和含硫化合物系列1)氟化物系列Ø稀土离子掺杂的氟化物晶体、玻璃(包括光纤)是上转换研究的重点和热点Ø氟化物基质的声子能量低，减少了无辐射跃迁的损失，具有较高的上转换效率尤其是重金属氟化物基质的振动频率低，稀土离子激发态无辐射跃迁的几率小，可增加辐射跃；同时，基质声子能量较低，一般在500-600cm1范围内，上转换效率高，是优良的激光上转换材料上转换材料Ø氟化物玻璃具有从紫外到红外光区(300-700nm)均呈透明、激活离子易于在其中掺杂和声子能量低等的优点，可用于上转换光纤激光器Nd3+掺杂的Pb5M3F19(M=Al、Ti、V、Cr、Fe、Ga)玻璃、Ho3+掺杂的BaY2F8、Pr3+掺杂的K2YF5玻璃是性能较好的上转换材料。

Ø钛Ti(Z=22), 钒V(Z=23) ，铬Cr(Z=24)，镓Ga(Z=31)，钬Ho(Z=67)，镨Pr(Z=59)，铅Pb (Z=82)Ø玻璃的优势在于：1.能够较大量地掺杂稀土离子；2.可制备均匀的大尺寸样品；3.可制成多种形态Ø氟化物玻璃已先后在微珠、光纤和块状形态获得激光振荡，尤其是光纤具有独特的优势上转换材料Ø稀土掺杂的氟化物的上转换效率较高，但其化学稳定性和机械强度差，抗激光损伤阈值低，制备工艺难度大，在一定程度上限制了它的应用Ø稀土掺杂的氟化物薄膜要克服晶体和玻璃制备困难、本钱高、环境条件要求高的缺点Ø如在CaF2(Ⅲ)基片上形成Er3+掺杂的LaF3薄膜，可将800nm的光高效地转换为538nm的可见光上转换材料2)氧化物系列氧化物上转换材料声子能量较高，因而上转换效率低但其优点是：制备工艺简单，环境条件要求低，形成玻璃相的组份范围大，稀土离子溶解度高，机械强度和化学稳定性好比较典型的氧化物上转换材料有Nd2(WO4)3，室温下可将808nm的激光转换为457nm和657nm的可见光；Er3+掺杂的YVO4可将808nm的激光转换为550nm的可见光以溶胶-凝胶法制备的Eu3+、Yb3+共掺杂的多组份硅酸盐玻璃可将973nm的光转换为橘黄色的光。

钇Y(Z=39)上转换材料Ø有些氧化物基质的声子能量也比较低，如TeO2在复合氧化物单晶中也有一些低声子能量的材料，YAl3(BO3)4(192.9cm1)、ZnWO4(199.5cm1)，可以作为激光上转换材料的基质Ø由于上转换激光器主要针对中、小功率场合的应用，对激光束要求较高，单晶中激活离子荧光谱线较窄，增益较高，且硬度、机械强度和热物理性能优于玻璃，故物化性能稳定的氧化物单晶常作为上转换材料的基质上转换材料3)氟氧化物系列作为上转换材料，氟化物的声子能量小，上转换效率高，但其最大的缺点是机械强度和化学稳定性差，给实际应用带来了很大的困难氧化物基质的机械强度和化学稳定性好，但声子能量大综合二者优点的氟氧化物的研究引起了人们的极大兴趣与氟化物玻璃相比，氟氧化物玻璃的激光损伤阈值、化学稳定性和机械强度等指标要优异得多比较典型的有Er3+掺杂的氟氧化物玻璃(Al2O3-CdF2-PbF2-YF3:Er3+)，激发波长为975nm，上转换波长为545nm、660nm和800nm 上转换材料Ø徐叙瑢研究组制备了一种不使用敏化剂的单掺杂Er3+的氟氧化物陶瓷，在980nm 光的激发下，可有效地发射红光和绿光，红光强度大于绿光，且红光强度随着Er3+浓度的增加而减弱，红光发射为双光子过程或三光子过程，绿光发射为三光子过程。

样品在980nm光激发下的上转换发光光谱左图(长波段发射光谱)： Er3+ 的摩尔分数分别为1%(a)、2%(b)和3%(c)右图(短波段发射光谱)： Er3+ 的摩尔分数分别为3%上转换材料Ø氟氧化物玻璃陶瓷(微晶玻璃)上转换材料是将稀土离子掺杂的氟化物微晶镶嵌于氧化物玻璃基质中，以它作为基体是一种便利和有效的方法Ø氟氧化物玻璃陶瓷利用成核剂诱发氟化物形成微小的晶粒，并使稀土离子先富集到氟化物微晶中，稀土离子被氟化物微晶所屏蔽，而不与包在外面的氧化物玻璃发生作用，这样掺杂的氟氧化物微晶玻璃既有氟化物基质的高转换效率，又有氧化物玻璃较好的机械强度和稳定性热处理后包埋于氧化物中的氟化物微晶颗粒为几十纳米，防止了散射引起的能量损失，含纳米微晶的氟氧化物玻璃陶瓷呈透明状上转换材料4)卤化物系列Ø氟化物具有上述缺点，促使人们寻找其它的基质材料卤化物上转换材料主要是稀土离子掺杂的原重金属卤化物，由于它们具有较低的振动能，减少了多声子驰豫的影响，能够提高转换效率Ø如：Er3+掺杂的Cs3Lu2Br9可将900nm的激发光有效地转换为500nm的蓝绿光此外，在ZnCl2和CdCl2基玻璃中，Zn-Cl和Cd-Cl的对称拉伸模量对称拉伸模量的振动频率分别是230290cm1 和243245 cm1，这些值比重金属氟化物玻璃的值还低几百个波数。

但氯化物玻璃对空气中的水份极其敏感，氯化物中空气中发生潮解，因而不可能在空气中制备玻璃和测量光谱上转换材料5)含硫化合物系列含硫体系上转换材料具有较低的声子能量但制备时不能与氧和水接触，须在密闭条件下进行以Pr3+为激活离子、Yb3+为敏化剂的Ga2O3-La2S3玻璃在室温下可将1046nm的光转换为480680nm范围的可见光其它基质：如稀土五磷酸盐非晶玻璃中可获得紫外上转换发光和蓝绿上转换发光稀土五磷酸盐是一种化学计量比晶体，高掺杂浓度、低猝灭、高增益和低阈值的优点使它得到应用，经特殊处理成为非晶材料后，不仅保存了晶态材料的优点，而且还克服了晶态材料基质易开裂和加工性能差的缺点上转换材料Ø就上转换发光效率而言，一般认为氯化物氟化物氧化物，这是单纯从材料的声子能量方面来考虑的，这个顺序恰与材料的结构稳定性顺序相反研究人员一直在探索，希望能发现既具有氯化物、氟化物那样高的上转换效率，又具有氧化物那样好的稳定性的基质材料Ø上转换发光的研究对上转换波长、效率与材料的结构、组成及制备条件的关系，尚缺乏系统的研究，在性能方面也尚需进一步完善和提高上转换发光的应用红外探测—作为红外光的显示材料将红外光转变成可见光，已到达实用化水平，如军用夜视镜材料、红外量子计数器或发光二极管材料。

防伪—将上转换材料添加在油墨、油漆或涂料中，印刷的文字或图形在特定的激发波长下显现；保密性强，不易仿制某上转换防伪油墨的激发(左)和发射光谱(右)上转换发光的应用Ø上转换激光器是实现全固体短波长激光器的方案之一用此法产生的激光已能覆盖整个可见光波段Ø其中性能最好的是用稀土离子掺杂的氟化锆基玻璃光纤为介质的上转换激光器，在室温下可产生连续激光，能量转换效率已超过20%，输出功率可达100mW以上Ø上转换材料LiYF4:Er3+，可将815nm泵浦光转换为550nm的绿色连续激光量子剪裁要求：能态结构要符合，E1和E2两个发光能级，E2E1和E1 G的跃都发射可见光，在E2向下的所有可能的跃迁中，几率P(E2E1)≫P(E2G) ，一个高能的紫外或真空紫外光子变成两个能量较低的可见光子这种现象称为量子剪裁，也称为量子劈裂或光子连续发射量子剪裁(a)发光材料能态的高能局部是连续的能带或相距很近的能级，电子在这样的能级驰豫到发光能级E1的过程中(2)，损失的能量以热能或红外光子的形式释放，无可见光子 产生，一个激发光(1)光子最多能产生一个可见光的发射光(3)光子；此时，即使量子效率接近100%，因驰豫过程消耗了较多能量，其能量效率比100%小得多。

b)在量子剪裁材料中，电子跃迁回到基态的过程中发射多个(图中为2-1和2-2两个)可见光子，量子效率大于1量子剪裁Energy level diagrams for two (hypothetical) types of lanthanide ions (I and II), showing the concept of downconversion. Type I is an ion for which emission from a high energy level can occur. Type II is an ion to which energy transfer takes place. (A) Quantum cutting on a single ion I by the sequential emission of two visible photons. (B) The possibility of quantum cutting by a two-step energy transfer. In the first step (indicated by ①), a part of the excitation energy is transferred from ion I to ion II by cross-relaxation. Ion II returns to the ground state by emitting one photon of visible light. Ion I is still in an excited state and can transfer the remaining energy to a second ion of type II (indicated by ②), which also emits a photon in the visible spectral region, giving a quantum efficiency of 200%. (C and D) The remaining two possibilities involve only one energy transfer step from ion I to ion II. This is sufficient to obtain visible quantum cutting if one of the two visible photons can be emitted by ion I.量子剪裁Energy level diagram of the Gd3+-Eu3+ system, showing the possibility of visible quantum cutting by a two-step energy transfer from Gd3+ to Eu3+.量子剪裁Emission spectra of LiGdF4:Eu3+(0.5 mol%) upon excitation in the 6IJ levels of Gd3+at 273 nm (violet line) and upon excitation in the 6GJ levels of Gd3+ at 202 nm (red line), both at 300 K. The spectra are scaled on the 5D17FJ emission intensity. (B) Excitation spectra of LiGdF4:Eu3+(0.5 mol%) monitoring the 5D17F2 emission of Eu3+ at 554 nm (violet line) and the 5D07F2 emission at 614 nm (red line), both at 300 K. The spectra are scaled on the 8S7/26IJ excitation intensity.量子剪裁From the R(5D0/5D1,2,3) values of 3.4 (for 6IJ excitation) and 7.4 (for 6GJ excitation), the ratio PCR/(PCR + PDT) was calculated to be0.9, showing that 9 of 10 Gd3+ ions in the 6GJ excited state relax through a two-step energy transfer to Eu3+, yielding two visible photons. One of 10 Gd3+ ions in the excited 6GJ state transfers all its energy directly to a high energy level of Eu3+, resulting in the emission of only one visible photon. In this way, a visible quantum efficiency of 190% can be obtained if nonradiative losses (for example, losses due to energy migration and energy transfer to nonradiative quenching centers in the lattice) can be prevented. Experience with lanthanide phosphors has shown that nonradiative losses can be low if the synthesis procedure is optimized. Thus, in an optimized LiGdF4:Eu3+ phosphor, a quantum efficiency close to 200% may be possible. Losses due to UV emission from Gd3+ are negligible; in the emission spectra, only very weak Gd3+ emission lines were observed. The intensity of these lines was much less than 1% of the total emission intensity, which shows that the energy transfer from Gd3+ to Eu3+ through energy migration is efficient.Here, PCR is the probability for cross-relaxation, and PDT is the probability for the direct energy transfer from Gd3+ to Eu3+. R(5D0/5D1,2,3) is the ratio of the 5D0 and the 5D1,2,3 emission intensities. The subscript (6GJ or 6IJ) indicates the excitation level for which the ratio is obtained.量子剪裁真空紫外激发下LiGdF4:Eu3+中两步能量传递引起的量子剪裁发光René T Wegh, Harry Donker, Koenraad D Oskam,Andries Meijerink.Visible Quantum Cutting in LiGdF4:Eu3+ Through Downconversion.Science, 1999, 283(5402): 663-666量子剪裁(1)真空紫外激发：Gd3+(8S7/2 6GJ)(2) Gd3+ (局部能量) 6GJ 6PJ  Eu3+(7FJ5D0)；(3) Eu3+( 5D07FJ) 发射一个红光光子；(4) Gd3+(6PJ 8S7/2)  Eu3+(7FJ 5D4)；(5) Eu3+ 5D4➟5D3,2,1,0 7FJ；发射光子；(6) Gd3+ (6PJ 7FJ) ➩(7FJ 6PJ)。

注意：1)逐步能量传递，使一个光子变成两个的过程，与逐次能量传递引起上转换的过程相反2)局部Gd3+ 的 激发态6GJ直接把能量传递给Eu3+的高能级，不参与两步能量传递，此过程只能产生一个可见光子，使此材料的量子效率小于200%量子剪裁两步能量传递：一、 Eu3+( 5D07FJ) 的红光发射，只激发到5D0；二、 Eu3+(5DJ 7FJ)的发射，和激发传递到Eu3+的高能级类似发射强度比：R = I(5D07FJ)/I(5D17FJ)R反映了参与两步能量传递的Gd3+的比例通过测量激发Gd3+的6G(202nm)(273nm)，只有到Eu3+的高能级的一步传递)时的R，可以估计材料的量子效率 LiGdF4:Eu3+的量子效率估计为190%quantum cutting via two-step energy transfer process with a visible quantum efficiency up to 194%Bo Liu, Yonghu Chen, Chaoshu Shi, Honggao Tang, Ye Tao. Visible quantum cutting in BaF2:Gd, Eu via downconversion. J. Lumin. 2003, 102(1-2): 155-159The emission spectra and excitation spectrum of BaF2:Gd, Eu(both1 mol% doping concentration)quantum cuttingHsin-Yi Tzeng, Bing-Ming Cheng, Teng-Ming Chen. Visible quantum cutting in green–emitting BaGdF5:Tb3+ phosphors via downconversion. J. Lumin. 2007, 122-123: 917-920The visible quantum cutting (QC) under the excitation at 215 and 187nm in a newly discovered BaGdF5:Tb3+ via downconversion mechanism has been observed and investigated. We have measured the vacuum ultraviolet (VUV) excitation and emission spectra and proposed possible mechanisms to rationalize the observed QC effect. In QC process, one short-wavelength UV or one VUV photon absorbed by Tb3+ was found to split into more than one visible photon emitted by Tb3+ through cross-relaxation and subsequent direct energy transfer between Tb3+ and Tb3+ and/or Gd3+ ions, depending on the excitation wavelength. On the basis of the calculations from the emission spectra in the visible region obtained, we have obtained optimal quantum efficiency as high as 168% and 180% for green-emitting BaGdF5:Tb3+ under excitation at 215 and 187 nm, respectively.quantum cuttingVUV and UV PL spectra of BaGdF5:5%Tb3+ upon excitation at 4f8-4f75d(LS) (187 and 215 nm) on Tb3+ (a) and (b) and 8S7/2-6IJ excitation (273 nm) on Gd3+ (c).VUV-UV PLE spectra of BaGdF5:5%Tb3+ monitored at 5D4-7F5 emission (543 nm) and 5D3-7F6 emission (380 nm) on Tb3+.quantum cuttingEnergy level diagrams for BaGdF5:5%Tb3+ showing (a) no QC when λex =273nm and the possible visible QC by a two-step energy transfer process when λex = (b) 215nm and (c) 187 nm.quantum cuttingThe calculated cross-relaxation (CR) quantum efficiency as a function of Tb3+-content for BaGdF5:x%Tb3+ under excitation of 187 and 215 nm.Upon excitation of quantum cutter Tb3+ with a high-energy photon, two photons in the visible range can be emitted through a two-step energy transfer (cross-relaxation and direct energy transfer) process from one Tb3+ to another neighboring Tb3+ and/or to the neighboring Gd3+ with a QE that exceeds 100%.quantum cuttingFor the practical calculation of extra QE, some essential premises will have to be proposed. For instance, the VU-VUV absorption by phosphors cannot be taken into account. Possible nonradiative losses due to energy migration at the defects and impurities in the samples must be ignored. For overall QE calculations involved in the QC processes, in addition to the QE for direct energy transfer from (i.e., 100%), we have also calculated the extra QE corresponding to cross-relaxation from Tb3+ to neighboring Tb3+ or from Gd3+ to neighboring Tb3+ through QC by using the following equation.PCR represents the probability for cross-relaxation and PDT is the probability for the direct energy transfer. R(5D4/rest) is the emission intensity ratio of the 5D4 to those attributed to 5D3 of Tb3+ and 6P7/2 of Gd3+ where the subscript indicates the excitation is from Tb3+ or Gd3+. If the QE of a phosphor via direct energy transfer is 100%, the extra QE for energy transfer via cross-relaxation is 65% and 48% for BaGdF5:5%Tb3+ under the excitation of 187 and 215 nm, respectively.Te-Ju Lee et al. Visible quantum cutting through downconversion in green-emitting K2GdF5:Tb3+ phosphors. Appl. Phys. Lett., 2006, 89: 131121 Visible quantum cutting under excitations at 212 and 172 nm in a green-emitting phosphor K2GdF5:Tb3+ 11% via a downconversion mechanism is investigated. The authors measured the vacuum ultraviolet VUV excitation and emission spectra and proposed mechanisms to rationalize the quantum-cutting effect. One short-UV or one VUV photon absorbed by Tb3+ is split into multiple visible photons emitted by Tb3+ through cross relaxation and direct energy transfer. Calculations indicate an optimal quantum efficiency as great as 189% for this phosphor.(Color online) Schematic energy levels of K2GdF5:Tb3+ showing possible mechanisms for visible QC under excitation of VUV with ex =(a)274, (b)212, and (c)172 nm; ① and ② denote cross relaxation and direct energy transfer, respectively.Song Ye, Bin Zhu, Jingxin Chen, Jin Luo and Jian Rong Qiu. Infrared quantum cutting in Tb3+,Yb3+ codoped transparent glass ceramics containing CaF2 nanocrystals. Appl. Phys. Lett., 2021, 92: 141112oxyfluoride glasses with compositions of 60SiO2–20Al2O3–20CaF2–0.3Tb3+–xYb3+ (x=0, 4, 6, 10, 14, 18, 22, 26, and 30)Color online Schematic energy level diagram of Tb3+ and Yb3+ with transitions that may be responsible for the cooperative energy transfer.Color online Left side: excitation spectra of Tb3+ 542 nm emission monitored in GC0 (red dashed line) and of Yb3+ 980 and 1016 nm emissions monitored in GC4 (blue dashed and dotted lines, respectively). Right side: emission spectra of GC0, GC4, and GC10 under excitation at 484 nm (solid lines in red, blue, and green, respectively.)the occurrence of cooperative energy transfer from the 5D4 level of Tb3+ to two Yb3+ ions, which subsequently lead to 950–1100 nm infrared emission. The quantum efficiency approaches 155% with 0.3Tb3+–26Yb3+ doping.Color online Quantum efficiency and Tb3+ 5D4→7F5 transitionlifetime as a function of Yb3+ concentration.Color online Luminescence decay curves of Tb3+ 542 nm emission originated from the 5D4→7F5 transition. Doping concentrations are 0.3Tb3+, xYb3+, with x=0, 4, 6, 10, 14, 18, 22, and 26, respectively.Q. Y. Zhang, C. H. Yang and Y. X. Pan. Cooperative quantum cutting in one-dimensional (YbxGd1−x)Al3(BO3)4:Tb3+ nanorods. Appl. Phys. Lett., 2007, 90: 021107 Near-infrared NIR quantum cutting (QC) involving the emission of two NIR photons per absorbed photon via a cooperative downconversion mechanism in one-dimensional (1D) (YbxGd1−x)Al3(BO3)4:Tb3+ nanorods has been demonstrated. The authors have analyzed the measured luminescence spectra and decay lifetimes and proposed a mechanism to rationalize the QC effect. Upon excitation of Tb3+ with a blue-visible photon at 485 nm, two NIR photons could be emitted by Yb3+ through an efficient cooperative energy transfer from Tb3+ to two Yb3+ with optimal quantum efficiency as great as 196%. The development of 1D Tb3+–Yb3+ QC nanomaterials could open up a possibility to realize high efficiency silicon-based solar cells by means of downconversion of the green-to-ultraviolet part of the solar spectrum to 1000 nm photons with a twofold increase in the photon number.(Color online) (a) XRD pattern and Raman spectrum of (Gd0.99Tb0.01)Al3(BO3)4 nanorods. (b) TEM image of the (Gd0.99Tb0.01)Al3(BO3)4 nanorods. c and d High-resolution TEM images of the (Gd0.99Tb0.01)Al3(BO3)4 nanorods and the corresponding selected area electron diffraction pattern.(Color online) (a) PLE spectra of the Tb3+ 5D4→7F4 emission 541 nm, solid line and the Yb3+:2F5/2→2F7/2 emission (980 nm, dotted line) and (b) visible-NIR PL spectrum upon excitation of 485 nm Tb3+:7F6→5D4 of 1D (Yb0.1Gd0.89Tb0.01)Al3(BO3)4. The inset shows decay lifetimes of the Tb3+:5D4→7F4 luminescence under excitation of 485 nm. The different fractions x of Yb3+ in the samples are indicated in the figure.(Color online) Schematic energy levels of (YbxGd1−x)Al3(BO3)4:Tb3+ showing possible mechanisms for a NIR QC under excitation of visible with ex=485 nm.Energy-transfer efficiency and quantum efficiency as a function of the Yb3+ concentration in 1D (YbxGd1−x)Al3(BO3)4:Tb3+.Q. Y. Zhang, G. H. Yang and Z. H. Jiang. Cooperative downconversion in GdAl3(BO3)4:RE3+,Yb3+(RE=Pr, Tb, and Tm). Appl. Phys. Lett., 2007, 91: 051903An efficient near-infrared (NIR) quantum cutting (QC) in GdAl3(BO3)4:RE3+,Yb3+ (RE=Pr, Tb, and Tm) phosphors has been demonstrated, which involves the conversion of the visible photon into the NIR emission with an optimal quantum efficiency approaching 200%, by exploring the cooperative downconversion mechanism from RE3+ (RE=Pr, Tb, and Tm) excitons to the two activator ions, Yb3+. The development of NIR QC phosphors could open up a new approach in achieving high efficiency silicon-based solar cells by means of downconversion in the visible part of the solar spectrum to 1000 nm photons with a twofold increase in the photon number.(Color online) Schematic energy level diagrams of GAB:Pr,Yb, GAB:Tb,Yb, and GAB:Tm,Yb, showing the concept of NIR QC with visible excitation at 489, 485, and 475 nm, respectively.(Color online) Visible-NIR PL spectra of (a) GAB:1%Pr,x%Yb (x=0, 2, 10, 20, and 30) (ex=489 nm), (b) GAB:1%Tb,2%Yb (ex =485 nm), and (c) GAB:1%Tm,2%Yb ( ex=475 nm).PLE spectra of RE3+(RE=Pr, Tb, and Tm) solid line and Yb3+ dotted line are also given.(Color online) Decay lifetimes of the Pr3+:3P0→3H6 luminescence under excitation of 489 nm. The different fractions x of Yb3+ in the samples are indicated in the figure. Inset shows decay curves in semilogrithmic plot.ETE (energy transfer efficiency) and decay lifetimes as a function of the Yb3+ doping concentration.The maximum QE (quantum efficiency) should be 165% at the Yb3+ doping concentration of 2 mol %. For GAB:Tb,Yb and GAB:Tm,Yb, the calculated optimal NIR QE approaches 167% and 164%, respectively, before reaching CQ (concentration quenching) threshold of 10 mol %.In summary, we conclude that an efficient NIR QC in GdAl3(BO3)4RE3+,Yb3+ (RE=Pr, Tb, and Tm) phosphors has been demonstrated, which involves the conversion of the visible photon from RE3+ (RE=Pr, Tb, and Tm) into the NIR of Yb3+ emission with the optimal QE approaching 200%. A possible mechanism of the NIR QC phenomenon has been proposed based on the measured luminescence spectra and decay lifetimes.。