上轉(zhuǎn)換和量子剪裁

1、上轉(zhuǎn)換和量子剪裁上轉(zhuǎn)換發(fā)光通常，PL發(fā)射波長比激發(fā)波長要長，說明過程中有能量損失，以熱能的形式損耗。上轉(zhuǎn)換(upconversion)發(fā)光：長波吸收，然后發(fā)出短波光的現(xiàn)象。上轉(zhuǎn)換材料過程不同于斯托克斯規(guī)那么及瓦維洛夫定律所涉及的過程。屬反斯托克斯現(xiàn)象。上轉(zhuǎn)換發(fā)光的效率隨著激發(fā)光強(qiáng)的增加而超線性地增長，所以，在激光的高密度激發(fā)下就容易觀察到最簡(jiǎn)單的上轉(zhuǎn)換現(xiàn)象發(fā)生在同一個(gè)或同一種發(fā)光中心上，它的發(fā)光過程分為三類。1一個(gè)中心同時(shí)吸收兩個(gè)光子然后發(fā)射一個(gè)大光子的疊加過程此類中心可以同時(shí)吸收兩個(gè)光子而到達(dá)激發(fā)態(tài)。激發(fā)態(tài)和基態(tài)之間并沒有中間的激發(fā)態(tài)，是一種雙光子吸收過程。雙光子吸收中的兩個(gè)光子可以有不同的

2、能量，即不同的頻率。但它們的能量之和要等于中心到達(dá)激發(fā)態(tài)時(shí)所需要的能量，即：h1+h2 = E2E1。 連續(xù)改變1，保持2恒定，當(dāng)發(fā)生吸收時(shí)即可得到E2E1的數(shù)值。CaF2:Eu2+，在紅寶石激光器的6943 譜線的強(qiáng)激發(fā)下，發(fā)射一個(gè)4250 光子。而此材料在6943 附近是透明的，不能吸收6943 的光。h1h22) 激發(fā)態(tài)吸收被光激發(fā)到激發(fā)態(tài)上的電子再吸收光子躍遷到更高能級(jí)。(a)發(fā)射光(3)光子能量小于激發(fā)光光子能量，通過與晶格的作用，有一局部能量轉(zhuǎn)變成熱能； (b)上轉(zhuǎn)換材料吸收激發(fā)光中的多個(gè)光子(1-1和1-2兩個(gè))發(fā)射一個(gè)光子，發(fā)射光子的能量大于激發(fā)光子的能量。2) 激發(fā)態(tài)吸收La

3、F3中Tm3+的能級(jí)和647.1nm激發(fā)下的上轉(zhuǎn)換過程氟F(Z = 9)，鑭La (Z = 57)， 銩Tm(Z = 69)一、多光子吸收(紅色)：(1)3H63F2；(2)3H4 1D2；3F4 1G4；(3)1G4 3P1。二、馳豫(綠色) ：3F2 3H4(3F2、3F3和3F4相距很近，電子很快馳豫到3H4)；3P1 1I6。三、輻射(黑色) ：(1)馳豫到3H4的電子3H4 3H6、3F4(IR)； (2)藍(lán)光：1G4 3H6480nm；1D2 3F4450nm；(3)紫外：1D2 3H6360nm；1I63F4340nm。激發(fā)態(tài)吸收中的吸收雪崩現(xiàn)象：基態(tài)吸收弱，激發(fā)態(tài)吸收強(qiáng)。1、基

4、態(tài)吸收較弱，開始時(shí)激發(fā)態(tài)E1上的電子不多，盡管激發(fā)態(tài)吸收強(qiáng)，到達(dá)E2上的電子也不多，上轉(zhuǎn)換發(fā)光較弱。2、 E1上電子數(shù)減少1個(gè)(激發(fā)態(tài)吸收)：E1 E2。3、交叉馳豫E2 E1G E1 (無基態(tài)吸收) ， E1能級(jí)上電子數(shù)倍增， 吸收激發(fā)光從E1 E2的電子數(shù)也倍增，上轉(zhuǎn)換增強(qiáng)。(1)激發(fā)態(tài)E1上的電子數(shù)增多； (2)基態(tài)G上的電子數(shù)減少；(3)E1上的電子經(jīng)由激發(fā)態(tài)吸收，而非基態(tài)吸收。弱吸收強(qiáng)吸收h2h13) 逐次能量傳遞Yb3+，Tm3+雙摻雜體系/鐿Yb (Z = 70)激發(fā)：960nm(IR)；發(fā)射：藍(lán)光。三步能量傳遞(1) Yb3+(2F5/22F2/7)Tm3+(3H6 3H5 3

5、F4)；(2) Yb3+(2F5/22F2/7)Tm3+(3F4 3F2,3 3H4)；(3) Yb3+(2F5/22F2/7)Tm3+(3H4 1G4)。處于激發(fā)態(tài)的同種離子之間的能量傳遞也能產(chǎn)生上轉(zhuǎn)換發(fā)光。在高的Tm3+濃度(1%)樣品中，兩個(gè)激發(fā)到3F3的Tm3+間發(fā)生交叉馳豫： (3F2,3 3H6) (3F2,3 1D2)3) 逐次能量傳遞W.F. Silva et al. Highly efficient upconversion emission and luminescence switching from Yb3+/Tm3+ co-doped water-free low s

6、ilica 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 nmluminescence swi

7、tchingThe 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

8、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) 逐次能量傳遞Er3+激發(fā): Yb3+Er

9、3+(能量傳遞)/鉺Er (Z = 68)(1) Yb3+(2F5/22F7/2)Er3+(4I15/24I11/2 4I13/2)(2)Er3+(4I11/24F7/2 4S3/2)(3)Er3+(4I13/24F9/2)Er3+發(fā)射:(1)4S3/24I15/2(550nm)(2)4F9/24I15/2(660nm)上轉(zhuǎn)換材料上轉(zhuǎn)換材料：?jiǎn)螕诫s和雙摻雜一摻雜離子單摻雜：利用稀土離子的f-f禁戒躍遷，窄線的振子強(qiáng)度小的光譜限制了對(duì)紅外光的吸收。效率低。如增加摻雜濃度來增加吸收，那么造成熒光的濃度猝滅。為提高紅外吸收能力，引入高濃度敏化劑(離子)，采用雙摻雜方法。上轉(zhuǎn)換材料雙摻雜，如：Yb3+

10、，其 2F7/22F5/2的躍遷吸收很強(qiáng)，且波長與950-1000nm的激光匹配良好，而它的激發(fā)態(tài)又高于激活離子Er3+(4I11/2)、Ho3+(5I6)、Tm3+(3H5)的激發(fā)亞穩(wěn)態(tài)，可將吸收的紅外光子能量傳遞給這些激活離子，發(fā)生雙光子或多光子的加和，從而實(shí)現(xiàn)發(fā)射短波長的光，上轉(zhuǎn)換過程明顯增加。因此， Yb3+作為敏化劑是提高上轉(zhuǎn)換效率的重要途徑之一。激光二極管泵浦源：GaAlAs、AlGaIn和InGaAs，發(fā)射波長范圍分別與一些稀土離子 (Nd3+、Tm3+、Er3+和Ho3+) 的主吸收帶匹配較好。上轉(zhuǎn)換材料Er3+是一種有效的上轉(zhuǎn)換激活離子，在800-1000nm范圍具有豐富的紅

11、外光子激發(fā)的能級(jí)。 Er3+在氟化物中的溶解度高， Er3+摻雜的氟化銦、氟鋯酸鹽和氟磷酸鹽是較好的綠光上轉(zhuǎn)換材料。影響摻雜的稀土離子發(fā)光性能的因素：稀土離子-陰離子的相互作用強(qiáng)，上轉(zhuǎn)換發(fā)光強(qiáng)度低；稀土離子周圍對(duì)稱性低，有利于提高上轉(zhuǎn)換發(fā)光強(qiáng)度；基質(zhì)晶格中陽離子的價(jià)態(tài)高，對(duì)上轉(zhuǎn)換發(fā)光有利。上轉(zhuǎn)換材料二基質(zhì)材料形態(tài)：晶體、玻璃和陶瓷基質(zhì)材料要求：光學(xué)性能好；具有一定的機(jī)械強(qiáng)度和化學(xué)穩(wěn)定性；基質(zhì)材料一般不構(gòu)成發(fā)光能級(jí)，但能為激活離子提供適宜的晶體場(chǎng)，使其產(chǎn)生特定的發(fā)射；基質(zhì)材料聲子能量小，有利于提高上轉(zhuǎn)換的效率?；|(zhì)材料對(duì)激光閾值功率和輸出效率也有很大影響。上轉(zhuǎn)換材料上轉(zhuǎn)換發(fā)光材料種類非常多，根據(jù)

12、基質(zhì)可分為5類：氟化物系列、氧化物系列、氟氧化物系列、鹵化物系列和含硫化合物系列。1)氟化物系列稀土離子摻雜的氟化物晶體、玻璃(包括光纖)是上轉(zhuǎn)換研究的重點(diǎn)和熱點(diǎn)。氟化物基質(zhì)的聲子能量低，減少了無輻射躍遷的損失，具有較高的上轉(zhuǎn)換效率。尤其是重金屬氟化物基質(zhì)的振動(dòng)頻率低，稀土離子激發(fā)態(tài)無輻射躍遷的幾率小，可增加輻射躍；同時(shí)，基質(zhì)聲子能量較低，一般在500-600cm1范圍內(nèi)，上轉(zhuǎn)換效率高，是優(yōu)良的激光上轉(zhuǎn)換材料。上轉(zhuǎn)換材料氟化物玻璃具有從紫外到紅外光區(qū)(300-700nm)均呈透明、激活離子易于在其中摻雜和聲子能量低等的優(yōu)點(diǎn)，可用于上轉(zhuǎn)換光纖激光器。Nd3+摻雜的Pb5M3F19(M=Al、Ti

13、、V、Cr、Fe、Ga)玻璃、Ho3+摻雜的BaY2F8、Pr3+摻雜的K2YF5玻璃是性能較好的上轉(zhuǎn)換材料。鈦Ti(Z=22), 釩V(Z=23) ，鉻Cr(Z=24)，鎵Ga(Z=31)，鈥Ho(Z=67)，鐠Pr(Z=59)，鉛Pb (Z=82)玻璃的優(yōu)勢(shì)在于：能夠較大量地?fù)诫s稀土離子；可制備均勻的大尺寸樣品；可制成多種形態(tài)。氟化物玻璃已先后在微珠、光纖和塊狀形態(tài)獲得激光振蕩，尤其是光纖具有獨(dú)特的優(yōu)勢(shì)。上轉(zhuǎn)換材料稀土摻雜的氟化物的上轉(zhuǎn)換效率較高，但其化學(xué)穩(wěn)定性和機(jī)械強(qiáng)度差，抗激光損傷閾值低，制備工藝難度大，在一定程度上限制了它的應(yīng)用。稀土摻雜的氟化物薄膜要克服晶體和玻璃制備困難、本錢高、

14、環(huán)境條件要求高的缺點(diǎn)。如在CaF2()基片上形成Er3+摻雜的LaF3薄膜，可將800nm的光高效地轉(zhuǎn)換為538nm的可見光。上轉(zhuǎn)換材料2)氧化物系列氧化物上轉(zhuǎn)換材料聲子能量較高，因而上轉(zhuǎn)換效率低。但其優(yōu)點(diǎn)是：制備工藝簡(jiǎn)單，環(huán)境條件要求低，形成玻璃相的組份范圍大，稀土離子溶解度高，機(jī)械強(qiáng)度和化學(xué)穩(wěn)定性好。比較典型的氧化物上轉(zhuǎn)換材料有Nd2(WO4)3，室溫下可將808nm的激光轉(zhuǎn)換為457nm和657nm的可見光；Er3+摻雜的YVO4可將808nm的激光轉(zhuǎn)換為550nm的可見光。以溶膠-凝膠法制備的Eu3+、Yb3+共摻雜的多組份硅酸鹽玻璃可將973nm的光轉(zhuǎn)換為橘黃色的光。釔Y(Z=39)

15、上轉(zhuǎn)換材料有些氧化物基質(zhì)的聲子能量也比較低，如TeO2。在復(fù)合氧化物單晶中也有一些低聲子能量的材料，YAl3(BO3)4(192.9cm1)、ZnWO4(199.5cm1)，可以作為激光上轉(zhuǎn)換材料的基質(zhì)。由于上轉(zhuǎn)換激光器主要針對(duì)中、小功率場(chǎng)合的應(yīng)用，對(duì)激光束要求較高，單晶中激活離子熒光譜線較窄，增益較高，且硬度、機(jī)械強(qiáng)度和熱物理性能優(yōu)于玻璃，故物化性能穩(wěn)定的氧化物單晶常作為上轉(zhuǎn)換材料的基質(zhì)。上轉(zhuǎn)換材料3)氟氧化物系列作為上轉(zhuǎn)換材料，氟化物的聲子能量小，上轉(zhuǎn)換效率高，但其最大的缺點(diǎn)是機(jī)械強(qiáng)度和化學(xué)穩(wěn)定性差，給實(shí)際應(yīng)用帶來了很大的困難。氧化物基質(zhì)的機(jī)械強(qiáng)度和化學(xué)穩(wěn)定性好，但聲子能量大。綜合二者優(yōu)點(diǎn)

16、的氟氧化物的研究引起了人們的極大興趣。與氟化物玻璃相比，氟氧化物玻璃的激光損傷閾值、化學(xué)穩(wěn)定性和機(jī)械強(qiáng)度等指標(biāo)要優(yōu)異得多。比較典型的有Er3+摻雜的氟氧化物玻璃(Al2O3-CdF2-PbF2-YF3:Er3+)，激發(fā)波長為975nm，上轉(zhuǎn)換波長為545nm、660nm和800nm。 上轉(zhuǎn)換材料徐敘瑢研究組制備了一種不使用敏化劑的單摻雜Er3+的氟氧化物陶瓷，在980nm 光的激發(fā)下，可有效地發(fā)射紅光和綠光，紅光強(qiáng)度大于綠光，且紅光強(qiáng)度隨著Er3+濃度的增加而減弱，紅光發(fā)射為雙光子過程或三光子過程，綠光發(fā)射為三光子過程。樣品在980nm光激發(fā)下的上轉(zhuǎn)換發(fā)光光譜左圖(長波段發(fā)射光譜)： Er3+

17、 的摩爾分?jǐn)?shù)分別為1%(a)、2%(b)和3%(c)右圖(短波段發(fā)射光譜)： Er3+ 的摩爾分?jǐn)?shù)分別為3%上轉(zhuǎn)換材料氟氧化物玻璃陶瓷(微晶玻璃)上轉(zhuǎn)換材料是將稀土離子摻雜的氟化物微晶鑲嵌于氧化物玻璃基質(zhì)中，以它作為基體是一種便利和有效的方法。氟氧化物玻璃陶瓷利用成核劑誘發(fā)氟化物形成微小的晶粒，并使稀土離子先富集到氟化物微晶中，稀土離子被氟化物微晶所屏蔽，而不與包在外面的氧化物玻璃發(fā)生作用，這樣摻雜的氟氧化物微晶玻璃既有氟化物基質(zhì)的高轉(zhuǎn)換效率，又有氧化物玻璃較好的機(jī)械強(qiáng)度和穩(wěn)定性。熱處理后包埋于氧化物中的氟化物微晶顆粒為幾十納米，防止了散射引起的能量損失，含納米微晶的氟氧化物玻璃陶瓷呈透明狀。

18、上轉(zhuǎn)換材料4)鹵化物系列氟化物具有上述缺點(diǎn)，促使人們尋找其它的基質(zhì)材料。鹵化物上轉(zhuǎn)換材料主要是稀土離子摻雜的原重金屬鹵化物，由于它們具有較低的振動(dòng)能，減少了多聲子馳豫的影響，能夠提高轉(zhuǎn)換效率。如：Er3+摻雜的Cs3Lu2Br9可將900nm的激發(fā)光有效地轉(zhuǎn)換為500nm的藍(lán)綠光。此外，在ZnCl2和CdCl2基玻璃中，Zn-Cl和Cd-Cl的對(duì)稱拉伸模量的振動(dòng)頻率分別是230290cm1 和243245 cm1，這些值比重金屬氟化物玻璃的值還低幾百個(gè)波數(shù)。但氯化物玻璃對(duì)空氣中的水份極其敏感，氯化物中空氣中發(fā)生潮解，因而不可能在空氣中制備玻璃和測(cè)量光譜。上轉(zhuǎn)換材料5)含硫化合物系列含硫體系上轉(zhuǎn)

19、換材料具有較低的聲子能量。但制備時(shí)不能與氧和水接觸，須在密閉條件下進(jìn)行。以Pr3+為激活離子、Yb3+為敏化劑的Ga2O3-La2S3玻璃在室溫下可將1046nm的光轉(zhuǎn)換為480680nm范圍的可見光。其它基質(zhì)：如稀土五磷酸鹽非晶玻璃中可獲得紫外上轉(zhuǎn)換發(fā)光和藍(lán)綠上轉(zhuǎn)換發(fā)光。稀土五磷酸鹽是一種化學(xué)計(jì)量比晶體，高摻雜濃度、低猝滅、高增益和低閾值的優(yōu)點(diǎn)使它得到應(yīng)用，經(jīng)特殊處理成為非晶材料后，不僅保存了晶態(tài)材料的優(yōu)點(diǎn)，而且還克服了晶態(tài)材料基質(zhì)易開裂和加工性能差的缺點(diǎn)。上轉(zhuǎn)換材料就上轉(zhuǎn)換發(fā)光效率而言，一般認(rèn)為氯化物氟化物氧化物，這是單純從材料的聲子能量方面來考慮的，這個(gè)順序恰與材料的結(jié)構(gòu)穩(wěn)定性順序相反。

20、研究人員一直在探索，希望能發(fā)現(xiàn)既具有氯化物、氟化物那樣高的上轉(zhuǎn)換效率，又具有氧化物那樣好的穩(wěn)定性的基質(zhì)材料。上轉(zhuǎn)換發(fā)光的研究對(duì)上轉(zhuǎn)換波長、效率與材料的結(jié)構(gòu)、組成及制備條件的關(guān)系，尚缺乏系統(tǒng)的研究，在性能方面也尚需進(jìn)一步完善和提高。上轉(zhuǎn)換發(fā)光的應(yīng)用紅外探測(cè)作為紅外光的顯示材料將紅外光轉(zhuǎn)變成可見光，已到達(dá)實(shí)用化水平，如軍用夜視鏡材料、紅外量子計(jì)數(shù)器或發(fā)光二極管材料。防偽將上轉(zhuǎn)換材料添加在油墨、油漆或涂料中，印刷的文字或圖形在特定的激發(fā)波長下顯現(xiàn)；保密性強(qiáng)，不易仿制。某上轉(zhuǎn)換防偽油墨的激發(fā)(左)和發(fā)射光譜(右)上轉(zhuǎn)換發(fā)光的應(yīng)用上轉(zhuǎn)換激光器是實(shí)現(xiàn)全固體短波長激光器的方案之一。用此法產(chǎn)生的激光已能覆蓋整

21、個(gè)可見光波段。其中性能最好的是用稀土離子摻雜的氟化鋯基玻璃光纖為介質(zhì)的上轉(zhuǎn)換激光器，在室溫下可產(chǎn)生連續(xù)激光，能量轉(zhuǎn)換效率已超過20%，輸出功率可達(dá)100mW以上。上轉(zhuǎn)換材料LiYF4:Er3+，可將815nm泵浦光轉(zhuǎn)換為550nm的綠色連續(xù)激光。量子剪裁要求：能態(tài)結(jié)構(gòu)要符合，E1和E2兩個(gè)發(fā)光能級(jí)，E2E1和E1 G的躍都發(fā)射可見光，在E2向下的所有可能的躍遷中，幾率P(E2E1)P(E2G) ，一個(gè)高能的紫外或真空紫外光子變成兩個(gè)能量較低的可見光子。這種現(xiàn)象稱為量子剪裁，也稱為量子劈裂或光子連續(xù)發(fā)射。量子剪裁(a)發(fā)光材料能態(tài)的高能局部是連續(xù)的能帶或相距很近的能級(jí)，電子在這樣的能級(jí)馳豫到發(fā)光

22、能級(jí)E1的過程中(2)，損失的能量以熱能或紅外光子的形式釋放，無可見光子 產(chǎn)生，一個(gè)激發(fā)光(1)光子最多能產(chǎn)生一個(gè)可見光的發(fā)射光(3)光子；此時(shí)，即使量子效率接近100%，因馳豫過程消耗了較多能量，其能量效率比100%小得多。(b)在量子剪裁材料中，電子躍遷回到基態(tài)的過程中發(fā)射多個(gè)(圖中為2-1和2-2兩個(gè))可見光子，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

23、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 (i

24、ndicated by ), 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 ), whi

25、ch 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 i

26、on 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 leve

27、ls of Gd3+ at 202 nm (red line), both at 300 K. The spectra are scaled on the 5D17FJ emission intensity. (B) Excitation spectra of LiGdF4:Eu3+(0.5 mol%) monitoring the 5D17F2 emission of Eu3+ at 554 nm (violet line) and the 5D07F2 emission at 614 nm (red line), both at 300 K. The spectra are scaled

28、on the 8S7/26IJ 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 be0.9, showing that 9 of 10 Gd3+ ions in the 6GJ excited state relax through a two-step energy transfer to Eu3+, yielding two

29、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 e

30、nergy 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 t

31、o 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 en

32、ergy 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

33、 the ratio is obtained.量子剪裁真空紫外激發(fā)下LiGdF4:Eu3+中兩步能量傳遞引起的量子剪裁發(fā)光Ren 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)真空紫外激發(fā)：Gd3+(8S7/2 6GJ)(2) Gd3+ (局部能量) 6GJ 6PJ Eu3+(7FJ5D0)；(3) Eu3+( 5D07FJ)

34、 發(fā)射一個(gè)紅光光子；(4) Gd3+(6PJ 8S7/2) Eu3+(7FJ 5D4)；(5) Eu3+ 5D45D3,2,1,0 7FJ；發(fā)射光子；(6) Gd3+ (6PJ 7FJ) (7FJ 6PJ)。注意：1)逐步能量傳遞，使一個(gè)光子變成兩個(gè)的過程，與逐次能量傳遞引起上轉(zhuǎn)換的過程相反。2)局部Gd3+ 的 激發(fā)態(tài)6GJ直接把能量傳遞給Eu3+的高能級(jí)，不參與兩步能量傳遞，此過程只能產(chǎn)生一個(gè)可見光子，使此材料的量子效率小于200%。量子剪裁兩步能量傳遞：一、 Eu3+( 5D07FJ) 的紅光發(fā)射，只激發(fā)到5D0；二、 Eu3+(5DJ 7FJ)的發(fā)射，和激發(fā)傳遞到Eu3+的高能級(jí)類似。

35、發(fā)射強(qiáng)度比：R = I(5D07FJ)/I(5D17FJ)R反映了參與兩步能量傳遞的Gd3+的比例。通過測(cè)量激發(fā)Gd3+的6G(202nm)(273nm)，只有到Eu3+的高能級(jí)的一步傳遞)時(shí)的R，可以估計(jì)材料的量子效率。 LiGdF4:Eu3+的量子效率估計(jì)為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 qua

36、ntum 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 greenemitting BaGdF5:Tb3+ phosphors v

37、ia 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 a

38、nd 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+ a

39、nd/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.qua

40、ntum 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 cuttingEnerg

41、y level diagrams for BaGdF5:5%Tb3+ showing (a) no QC when ex =273nm and the possible visible QC by a two-step energy transfer process when ex = (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 excita

42、tion 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+ w

43、ith 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

44、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

45、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 f

46、rom 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

47、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 prop

48、osed 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 phospho

49、r.(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; and denote cross relaxation and direct energy transfer, respectively.Song Ye, Bin Zhu, Jingxin Chen, Jin Luo and Jian Rong Qiu. Infrared

50、quantum cutting in Tb3+,Yb3+ codoped transparent glass ceramics containing CaF2 nanocrystals. Appl. Phys. Lett., 2021, 92: 141112oxyfluoride glasses with compositions of 60SiO220Al2O320CaF20.3Tb3+xYb3+ (x=0, 4, 6, 10, 14, 18, 22, 26, and 30)Color online Schematic energy level diagram of Tb3+ and Yb3

51、+ 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: emissi

52、on 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 9501100 nm infrared emission. The quantum efficiency approaches 155% w

53、ith 0.3Tb3+26Yb3+ doping.Color online Quantum efficiency and Tb3+ 5D47F5 transitionlifetime as a function of Yb3+ concentration.Color online Luminescence decay curves of Tb3+ 542 nm emission originated from the 5D47F5 transition. Doping concentrations are 0.3Tb3+, xYb3+, with x=0, 4, 6, 10, 14, 18,

54、22, and 26, respectively.Q. Y. Zhang, C. H. Yang and Y. X. Pan. Cooperative quantum cutting in one-dimensional (YbxGd1x)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

55、downconversion mechanism in one-dimensional (1D) (YbxGd1x)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

56、, 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 mean

57、s 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-resolu

58、tion 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+ 5D47F4 emission 541 nm, solid line and the Yb3+:2F5/22F7/2 emission (980 nm, dotted line) and (b) visible-NIR PL spectrum upon excitatio

59、n of 485 nm Tb3+:7F65D4 of 1D (Yb0.1Gd0.89Tb0.01)Al3(BO3)4. The inset shows decay lifetimes of the Tb3+:5D47F4 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 (YbxGd1x)Al3(BO3)4:Tb3+ showi

60、ng 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 (YbxGd1x)Al3(BO3)4:Tb3+.Q. Y. Zhang, G. H. Yang and Z. H. Jiang. Cooperative downconversion in GdAl3(BO3)4:RE3+,Yb3+(RE=Pr, T