Abstract: A borate single crystal which can stably perform light wavelength conversion with high efficiency down to the ultraviolet region is represented by the chemical formula (A2O).(B2O3)x, and is an orthorhombic crystal belonging to the P212121 space group, wherein A includes two elements selected from the group consisting of Li, Na, K, Rb, and Cs, and 1.5<x<2.5.

Abstract: An infrared light-excited light-emitting substance given by the general formula:R1.sub.x R2(.sub.1-x)Ba.sub.z Cl.sub.3+2z where R1 is a rare-earth element, x satisfies the relation 0.01<x.ltoreq.1, R2 is another rare-earth element, and z satisfies the relation 1<z<4. Preferably, the substance is a transparent crystal having a transparency exceeding 70% in a wavelength range from 400 to 1500 nm, excluding wavelengths absorbed by rare-earth ions. The light-emitting substance can convert infrared light into visible light in a wavelength range from blue light to green light at a high conversion efficiency.

Abstract: Phosphorus concentration in molten copper can be determined by measuring temperature and electric resistivity of molten copper.

Abstract: Disclosed herein is an amorphous material in the form of foil for the regenerator, which is prepared by quenching a melt of a rare earth alloy by injection toward the surface of a roll running at a high speed, said alloy being composed of one or more rare earth elements in an amount of 50-99 atomic %, with the remainder being one or more iron family elements. This amorphous material has a large, stable specific heat capacity at very low temperatures.

Abstract: The present invention provides heat reserving materials comprising alloys of Ru and at least one rare earth metal which are represented by the formula (I):(A.sub.1-x B.sub.x).sub.z Ru.sub.1-y C.sub.ywherein A represents one or two or more of Er, Ho and Dy; B represents one or two or more of the other rare earth metals; C represents one or two or more of Co, Ni, Al, Cu, Pd, Rh, Au, Ag, Cr, Mn, V and B; x is not less than 0 and not more than 0.5; y is not less than 0 and less than 1.0; and z is more than 1.1 and less than 5.0.When the heat reserving materials of the present invention are used in a cryogenic refrigerator, very low temperatures of not higher than 10 K. can be achieved. Specific heat properties of the materials can be varied as desired by adjusting the content ratio of the plural phases each of which has a different magnetic transition temperature.