Preparation, Structure And Photoluminescence Properties Of Ge Nanoparticles Dispersed In Ceramic Matrix

Nano-sized Ge embedded in dielectric matrix has received considerable attention in recent years due to both excellent optical characteristics and wide application in optoelectronic and quantum device. However, most investigations were only concerned with the Ge nanoparticles embedded in SiO₂ matrix, There are a few reports on the preparation of Ge nanoparticles embedded in dielectric ceramic matrix. In fact, ceramic materials have excellent mechanical properties, outstanding thermal stability, wear resistance and chemical stability. In the meantime, ceramic would be a well-characterized material to passivate Ge nanoparticles surfaces, which will extend future application in photoluminescence field.In this paper, Al_4+2xGe_2-2xO_10-x (0.25≤x≤0.40) and Al₁₂(Si_4-xGe_x) O₂₆ (03)₃, Si(OC₂H₅)₄ and Cl₃GeCH₂CH₂COOH as precursors. The formation process of mullite phase was monitored by TG-DSC, XRD and FT-IR. After the reduction of Al₆Ge₂O₁₃ and Al₁₂Si_3.75Ge_0.25O₂₆ ceramic powder, strong room temperature photoluminescence (PL) was observed.It is shown that the PL intensity depends on the reduction temperature and duration. The best reduction parameter is 550℃in Al-Ge-O system and 500℃in Al-Si-Ge-O system for 3 hours, respectively. With the change of composition and reduction parameter, the peak position has no evident shift, and the peaks are almost located at 564, 611, 681, 730, and 774nm. The sample before reduction has no PL phenomenon under the same conditions. The average particle sizes of Ge clusters in the samples with highest PL intensity are 1.98 and 1.95nm detected by Raman spectra in two systems.The samples with highest PL intensity were reduced again at low temperature. The structure and properties were characterized by PL and Raman spectra. After further reduction, both the PL intensity and the particle size of Ge have increased. The samples further reduced at 400℃show the highest PL intensity and the mean size of Ge is 2.45 and 2.22nm, respectively. The mechanism of photoluminescence was discussed. It can be concluded that the PL is influenced by many factors, such as quantum confinement effect, dielectric confinement effect, phonon confinement effect, and the morphology of Ge nanoparticles. The luminescence process can be explained as the recombination between the relaxing surface electron(or hole) and the internal hole(or electron). The PL phenomenon is arised from Ge nanoparticles with the average size of about 2nm.