and examples are now extremely rare. Moser also blended praseodymium with neodymium to produce "Heliolite" glass ("Heliolit" in German), which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange "Praseodymium Yellow" stain for ceramics, which is a solid solution in the zircon lattice. This stain has no hint of green in it; by contrast, at sufficiently high loadings, praseodymium glass is distinctly green rather than pure yellow. Like many other lanthanides, praseodymium's shielded f-orbitals allow for long excited state lifetimes and high luminescence yields. Pr3+ as a dopant ion therefore sees many applications in optics and photonics. These include DPSS-lasers, single-mode fiber optical amplifiers, fiber lasers, upconverting nanoparticles as well as activators in red, green, blue, and ultraviolet phosphors. Silicate crystals doped with praseodymium ions have also been used to slow a light pulse down to a few hundred meters per second. As the lanthanides are so similar, praseodymium can substitute for most other lanthanides without significant loss of function, and indeed many applications such as mischmetal and ferrocerium alloys involve variable mixes of several lanthanides, including small quantities of praseodymium. The following more modern applications involve praseodymium specifically or at least praseodymium in a small subset of the lanthanides: In combination with neodymium, another rare-earth element, praseodymium is used to create high-power magnets notable for their strength and durability. In general, most alloys of the cerium-group rare earths (lanthanum through samarium) with 3d transition metals give extremely stable magnets that are often used in small equipment, such as motors, printers, watches, headphones, loudspeakers, and magnetic storage. Praseodymium–nickel intermetallic (PrNi5) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero. As an alloying agent with magnesium to create high-strength metals that are used in aircraft engines; yttrium and neodymium are also viable substitutes. Praseodymium is present in the rare-earth mixture whose fluoride forms the core of carbon arc lights, which are used in the motion picture industry for studio lighting and projector lights. Praseodymium compounds give glasses, enamels and ceramics a yellow color. Praseodymium is a component of didymium glass, which is used to make certain types of welder's and glass blower's goggles. Praseodymium oxide in solid solution with ceria or ceria-zirconia has been used as an oxidation catalyst. Due to its role in permanent