PROCESS FOR PRODUCING QUANTUM SPLITTING PHOSPHORS AND NOVEL COMPOSITIONS The invention was first conceived or reduced to practice in the performance of work under a United States Government contract with NIST, having Government Contract Number 0670 NANB 3H1372. The Government may have certain rights to the invention. FIELD OF THE INVENTION This invention relates to a process for producing quantum splitting phosphors and novel compositions. More specifically, this invention relates to quantum splitting in a host lattice by activating the host with the praseodymium ion in the +3 state (Pr+3) . Even more specifically, this invention relates to rules for obtaining a quantum splitting phosphor. BACKGROUND OF THE INVENTION Quantum splitting is generally described as the conversion of a single ultraviolet photon into two visible photons with the result that the quantum efficiency of luminescence exceeds unity. Quantum splitting materials are desirable for use as phosphors in applications requiring light to be generated. A suitable quantum splitting material can in principle produce a significantly brighter light source. Quantum splitting has been demonstrated previously in fluoride-base materials. A material comprising 0.1% Pr+3 in a matrix of YF3 has been shown to generate more than one visible photon for every absorbed ultraviolet (UV) photon when excited with 185nm radiation. The measured quantum efficiency of this material was 145%±15%, and thus greatly exceeded unity. The critical conditions that yield quantum splitting by the Pr+3 ion have been achieved in fluoride-based materials. Recently, quantum splitting in oxide host lattices activated by Pr+3 have been disclosed by applicants in an oxide material having the formula: Lai-xPrxMgB5O10, where 0