Zn_{1-x}Ni_xTe semiconductor nanocrystals in transparent glass for optoelectronic device applications

Abstract

Doping glass with semiconductors, particularly with nanostructured semiconductors, has attracted attention due to the large optical absorption cross-sections of the latter. Based on this property, Ni^{2+} (5 wt%) doped phosphate glass and Zn_{1-x}Ni_xTe (x = 0.5, 1.0, 5.0 and 10.0 wt% of Ni^{2+}) nanocrystals (NCs) doped phosphate glasses (GCs) were prepared by fusion method and subsequent heat treatment. Influence of Ni^{2+} on structural, thermo-optical and third-order nonlinear optical properties have been analysed through various spectroscopic characterizations. The XRD pattern of the glass (G) exhibits the amorphous nature of the host material while GCs exhibit not only amorphous halo but also the presence of quantum dots (QDs) or nanocrystals (NCs) phases. TEM analysis of the studied GCs samples confirm the presence of quantum dots (QDs) and bulk NCs with an average diameter of approximately 4.2 {pm } 0.3 nm and 13.4 {pm } 0.2 nm, respectively. Several phosphate groups were observed and reported from Raman and FTIR-ATR spectra. The absorption band positions confirmed that Ni^{2+} ions resemble to the octahedral symmetry. The intensity of absorption band around 1352 nm (^3T{_1}(F) rightarrow^3A{_2}(F)) increased with the increase of Ni^{2+} in GCs which is an indicative of the ^{[6]}Ni^{2+} coordination. The emission properties such as emission cross-sections ({sigma }_{emi}) full width at half maxima (FWHM) for the ^1T{_2}(D) rightarrow^3T{_2}(F) (visible) and ^3A{_2}(F) rightarrow^3T{_1}(F) (near-infrared) emission transitions were reported. Among the glass-containing semiconductor nanocrystals (GCs), the emission cross-sections in GC4 sample (x = 10% of Ni^{2+}) are the largest for both the visible (11.88 times 10^{-18} cm^2) and infrared (0.98 times 10^{-20} cm^2) transitions. Thermal diffusivity (D), thermal conductivity (K) and temperature dependent optical path length change (ds/dT) were obtained through time-resolved thermal lens (TL) and thermal relaxation (TR) methods. The D and K parameters do not change significantly with increase of Ni^{2+} ions (0.5–5%) in GCs. Nonlinear-refractive index and nonlinear absorption of the studied samples were also obtained using femtosecond Z-scan technique. The increase of nonlinear absorption coefficient (beta) is observed from GC2 (2.53 {times } 10^{-10} cm/W) to GC4 (7.98 {times } 10^{-10} cm/W). The GC4, sample with 10 wt% of Ni^{2+}, showed the lowest ds/dT (1.22 times 10^{-6} K^{-1}) with good lasing (FOM and emission cross-sections) and nonlinear absorption properties suggesting that it can be a good candidate for visible-red emission light conversion in LED technology.