In order to enhance dispensing technology towards an industrial application in Silicon Photovoltaics, in particular throughput rate has to be increased. For this reason, a novel parallel high precision fine line dispensing unit is currently being developed at Fraunhofer ISE providing one nozzle per contact finger and a central Paste supply. In order to ensure a homogeneous paste distribution to all nozzles, the influence of paste rheology on the flow profile of the dispensing nozzles was analyzed. An analytical comparison of two different dispensing pastes with water gave a good insight on the influence of paste rheology on flow patterns inside the dispensing nozzles. Furthermore, numerical CFD-simulation (CFD: Computational Fluid Dynamics) was used to investigate different nozzle geometries and finally print head designs. In various iteration steps, the influence of fabrication tolerances especially concerning the nozzle geometry was isolated and print head designs were optimized based on CFD towards maximum process stability. In the meantime, process optimization using a single nozzle approach led to an average finger width below 35 μm, confirmed by several characterization methods

Polycrystalline powders of La3Ga5SiO14 (LGSi), La3Ga5GeO14 (LGGe), and La3Ga5TiO14 (LGTi) doped with Eu3+ were studied with respect to their use as luminescent materials in solid state lighting based on light-emitting diodes. The langasites were synthesized with up to 35% of trivalent europium to achieve the highest possible doping amount. According to diffuse reflection measurements the undoped compounds have band gap energies of 4.51 eV (LGSi), 4.54 eV (LGGe) and 4.07 eV (LGTi). The luminescence behavior between 77 K and 500 K was investigated, including excitation, emission and lifetime measurements to analyze the impact of the structural differences between the three langasites on the spectroscopic properties of the materials. Depending on the excitation wavelengths, 300 nm (charge transfer) and 394 nm (4f levels, i.e.7F0 → 5L6), different quenching temperatures were achieved for LGSi : Eu3+ 20% (TQ,300 = 438 K, TQ,394 = 422 K), LGGe : Eu3+ 20% (TQ,300 = 325 K, TQ,394 = 441 K) and LGTi : Eu3+ 20% (TQ,300 = 500 K, TQ,394 = 467 K). The quenching observed can be explained by three semi-quantitative configurational coordinate diagrams. Independent from the excitation wavelength and the temperature (77-300 K) decay times of 1.1 ms were measured. At room temperature and with an excitation wavelength of 394 nm maximum quantum efficiencies of 40% for LGSi : Eu, of 80% for LGGe : Eu, and of 81% for LGTi : Eu were reached. Finally, to prove the applicability as red LED phosphors, the langasites were built into LEDs with (In,Ga)N chips emitting at 394 nm.

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