玻璃中CdSeS纳米晶体的室温光致发光谱

对掺有过饱和的镉、硒和少量硫的玻璃在500～800℃分别退火4h,生长了不同尺寸的CdSe_1-xS_x纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300～800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600～650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。

Photoluminescence of CdSeS Nanocrystals at Room Temperature

CdSe_1-xS_x nanocrystals were grown by annealing silica glass with supersaturate Cd,Se and S at 500～800℃ for 4h, respectively. The absorption and photolumines cence (PL) of the nanocrystals excited with light of different wavelength were measu red at room temperature. The PL spectra were discussed. In the sample annealed at 550℃, no absorption and emission were observed in the range of 300～800nm. This suggested that no CdSe_1-xS_x nanocrystals formed. The absorption of 1S_3/2-1S_e shifted toward to red with the rising of growth temperatures from 600～800℃ due to the weakening of quantum confinement with the increase of nanocrystal sizes. Mainly broadened peaks named H and L bands, H band corresponding to recombination at the band edge and L band corresponds to radiative recombination as sociated with deep traps, were observed in the grown at 600～650℃. As the growth temperature was raised higher, L bands disappeared gradually and only H bands were observed. This indicated that deep trap density decreased with the increase of growth temperature and the deep traps mainly were surface states. H bands shifted red with the increase of nanocrystal growth tempe ratures. This was due to quantum size effects because nanocrystal mean size increased with the increase of growth temperature. In the nanocrystals grown at 650 ～800℃, a series of obvious small peaks superposed on the broadened bands were also observed. The peak energy for nanocrystals grown at different temperatures was similar and only new peaks were observed in samples grown at lower temperatures. The superposed peaks could be divided into two groups. Within each group, the peaks distributed periodically withenergy separation of 120meV. There was 50me Venergy separation between the two groups. The energy separation was much hig her than that of LO phonon. Size-selective PL spectra of nanocrystals collected using excitation wavelength between 488～650nm indicated that the superposed peak energy did not change with the excited wavelength, only the relative intensity varied with the excitation wavelength.