Abstract: Neodymium ultraphosphates having the formulaMe.sub.x Nd.sub.1-x P.sub.5 O.sub.14wherein Me represents scandium, gallium, yttrium, indium, lanthanum, cerium, gadolinium, lutetium, thallium and/or uranium, and x is a number between 0 and 0.999, in the form of untwinned crystals, are prepared by heating Nd.sub.2 O.sub.3 and Me.sub.2 O.sub.3 in a vessel consisting of fine gold or of an inert, dense, carbon-based material with an excess of high-purity, anhydrous phosphoric acid or diphosphoric or polyphosphoric acid at a temperature between about 500.degree. and 600.degree. C, until the desired crystal size is achieved and then separating excess phosphoric acid or polyphosphoric acid, as the case may be.

Abstract: An infrared rays excited - infrared rays emitting fluorescent material which contains predetermined quantities of neodymium and ytterbium as activators is disclosed.The fluorescent material according to this invention is higher in the luminescence intensity than a conventional, infrared rays excited - infrared rays emitting fluorescent material which is activated with neodymium only. Moreover, its maximum luminescence wavelength lies within a wavelength region which a silicon photosensor can detect at high sensitivity. It is therefore very useful in practical use.The fluorescent material is represented by the following formula:MM'.sub.1-x-y Nd.sub.x Yb.sub.y P.sub.4 O.sub.12wherein M denotes at least one element selected from the group consisting of Li, Na, K, Rb and Cs, and M' denotes at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Ga and In, and where 0.05 .ltoreq. x .ltoreq. 0.999, 0.001 .ltoreq. y .ltoreq. 0.950, and x + y .ltoreq. 1.0.BACKGROUND OF THE INVENTION1.

Abstract: A highly doped optical amplifier in the form of a thin layer or fiber wherein the pump light is directed transversely to the surface of the layer or fiber. A transparent substrate is provided underneath the layer or fiber and a solar cell is provided in light receiving relationship to light passing through the layer or fiber on the opposite side of the substrate.