NOVELTY - A dispersion comprises elemental silicon/germanium nanoparticles (at least 1 wt.%) having an average primary particle diameter of not greater than 50 nanometers.    USE - As screen printing paste; as ink (claimed) such as inkjet inks, gravure printing inks and silicon inks, which are useful for forming components of solar cells or of electronic devices (such as thin film transistors useful for gating display structures e.g. active matrix liquid crystal displays, electrophoretic displays, and organic light emitting diode displays); and as a coating material.    ADVANTAGE - The dispersion is a good dispersion; has total metal contamination of not greater than 1 or not greater than 500 parts per million by weight; has a Z-average secondary particle size of not greater than 200 or not greater than 150 nm; has a viscosity of 2-25 mPa.s and surface tension of 20-70 dynes/cm; has a viscosity of 10-300 Pa.s; provides screen printing paste having a viscosity of 10-300 (preferably 50-250) Pa.s; provides screen printing paste having a viscosity of 10-800 Pa.s at a shear rate of 2 second-1; and also provides ink having a viscosity of 0.1-100 mPa.s and a surface tension of 20-70 dynes/cm. The dispersion comprising silicon/germanium particles are free of non-solvent based chemically bonded organic surface modification.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a collection of silicon/germanium nanoparticles having an average primary particle diameter of not greater than 100 nm and a level of total metal contamination of not greater than 5 parts per million;    (2) a paste comprising (wt.%): elemental silicon/germanium nanoparticles having an average primary particle size of not greater than 50 nm (at least 5), first solvent (0.25-15) having a boiling point of 55-160 degrees C, and second solvent (65-94.75) having a boiling point of at least 175 degrees C;    (3) an ink comprising (wt.%): elemental silicon/germanium nanoparticles (at least 1) having an average primary particle size of not greater than 30 nm, alcohol (10-60), and polar aprotic solvent (30-80);    (4) preparing (M1) an ink with elemental silicon/germanium nanoparticles, involving adding a second solvent to an initial dispersion of elemental silicon nanoparticles dispersed in a first solvent to form the ink which is a good dispersion of the nanoparticles in a blend of the solvents, where the elemental silicon/germanium nanoparticles are free from non-solvent based chemically bonded surface modification with an organic compound and where the first solvent and the second solvent blend to form a single phase;    (5) forming (M2) a screen printing paste with a selected viscosity based on adjusting the nanoparticle concentration, where the screen printing paste comprises elemental silicon/germanium nanoparticles, involving dispersing the nanoparticles in a solvent comprising a blend of a first solvent having a boiling point of 55-160 degrees C and a second solvent having a boiling point of 175 degrees C to form the paste, where the paste has a particle concentration of 10-20 wt.%;    (6) method (M3) for printing a desired thickness of a silicon nanoparticle ink, where the ink comprises elemental silicon/germanium nanoparticles (1 wt.%) having an average primary particle diameter of not greater than 50 nanometers, involving printing a first time the silicon nanoparticle ink to form a first silicon nanoparticle deposit; and repeating the printing at least one time as appropriate to get a desired thickness of the nanoparticle ink deposit;    (7) a laser pyrolysis apparatus (A1) comprising a reaction chamber, a light source and associated optical elements configured to deliver a light beam through the reaction chamber, a reactant delivery system containing reactant reservoirs, a nozzle configured to deliver reactants from the reactant delivery system into the reaction chamber, and a collection system configured to receive the flow from the reaction chamber that originated from the nozzle, where the nozzle comprises inner inert gas channel, intermediate reactant channel surrounding the inner inert gas channel and outer inert gas channel surrounding the intermediate reactant channel, where the inner inert gas channel and the outer inert gas channel are operably connected to an inert gas source; and    (8) synthesizing (P1) nanoparticles by laser pyrolysis, involving either reacting a reactant flow using a light beam to drive the reaction, where a reactant flow is initiated from a nozzle with reactants flowed through an annular ring with inert gases flowed through an inner flow channel in center and through an outer gas channel surrounding the reactant flow, where the reactant flow completely flows through a light beam such that energy from the light beam drives the reaction to form product particles; or reacting a reactant flow using a light beam to drive the reaction, where a reactant flow is initiated from a nozzle with reactants flowed through a reactant inlet with inert gases flowed through a quench gas inlet approximately surrounding the flow from the reactant inlet and an inert entrainment gas flows through an outer gas channel approximately surrounding the inert quench gas flow, where the reactant flow completely flows through a light beam such that energy from the light beam drives the reaction to form product particles and where the entrainment gas flow is at a volume at least 25% greater than the inert quench gas flow and the entrainment gas flow leaving the nozzle at a greater velocity than the inert quench gas flow.