The invention relates to an arrangement for the coating of substrates, which comprises an evaporation source and a vapor barrier between the evaporation source and the substrate. The vapor barrier is maintained at a temperature which is at least equal to or above the vaporization temperature of the material to be vaporized. The vapor barrier is implemented as a quartz valve, which includes a spherical closure part connected with a movable rod. In a first position this spherical closure part closes a vapor conducting tube, which is connected with the evaporation source, and, in a second position, the spherical closure part abuts a spherical calotte which seals off a quartz tube.