铒铥共掺氧化锌薄膜近红外宽带发射及变温行为的研究∗

摘要

采用磁控共溅射技术制备了铒铥共掺杂氧化锌发光薄膜.通过优化退火温度,实现了薄膜的近红外平坦宽带发射,总带宽可达到∼500 nm,覆盖了光通信S+C+L+U区波段.此发射带由Er3+的1535 nm (4I13/2→4I15/2)发射峰及Tm3+的1460 nm (3H4→3F4),1640 nm (1G4→3F2),1740 nm (3F4→3H6)发射峰组成.研究表明：退火温度低于800◦C时,没有观察到薄膜样品明显的光致发光现象；随着退火温度从800◦C升高到1000◦C, I1640/I1535发射峰强度比从0.2升高到0.3, I1740/I1535发射峰强度比从0.5降低到0.4,发射峰强度比均基本保持稳定；当退火温度高于1000◦C时, I1640/I1535发射峰强度比从0.3升高到0.6, I1740/I1535发射峰强度比从0.4升高到0.8,发射峰强度比均急剧增加.变温行为表明：随着温度从10 K逐渐升高到300 K,谱线的总带宽基本不变,在340—360 nm之间；Tm3+在1640和1740 nm处的发射峰强度分别降低了2/3和1/2, Er3+在1535 nm的发射峰强度增大了1.2倍.这是因为随着温度的升高,声子数目增多, Er3+与Tm3+离子之间发生能量传递的概率不断变大,并且在Tm3+离子之间没有发生交叉弛豫现象.%Er-Tm codoped ZnO thin film is synthesized by co-sputtering from separated Er, Tm, and ZnO targets. A flat and broad emission band is achieved in a range of 1400–2100 nm by optimizing annealing temperature, and the observed 1460, 1540, 1640 and 1740 nm emission bands are attributed to the transitions of Tm3+: 3H4→3F4, Er3+ 4I13/2→4I15/2, Tm3+1G4→ 3F2 and Tm3+ 3F4→ 3H6 transitions, respectively, which cover S, C, L, U bands. The intensity ratios of 1640 to 1535 nm and 1740 to 1535 nm below 1000 ◦C are nearly constant, while the ratios increase sharply above 1000 ◦C. The temperature dependence of photoluminescence (PL) spectrum is studied under 10–300 K. With increasing the operation temperature, the bandwidth of broadband is nearly invariable (340–360 nm), and the Tm3+ PL emission intensities of 1640 nm and 1740 nm from Er-Tm co-doped ZnO thin film decrease by a factor of 1.5 and 2, respectively. Moreover, the 1535 nm emission intensity is increased by a factor of 1.2. This phenomenon is attributed to the complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and the increase of phonon-assisted ET rate with temperature as well. And the cross relaxation between Tm3+ ions does not occur.