A series of RECa4O(BO3)(3) (RECOB) thin films (RE = Rare earth elements) was fabricated on ultrasmooth GdCOB (0 1 0) substrates by laser molecular beam epitaxy (MBE) method to explore the optimal growth conditions and to evaluate the luminescent properties. The growing surface of the film on a temperature gradient substrate was diagnosed with scanning reflection high energy electron diffraction (S-RHEED) system for quickly specifying optimum growth temperature and its dependence of rare earth element. The lowest temperature for epitaxial film growth was defined by the appearance of streak pattern in RHEED and it reflected the lattice matching with the substrate. TbCCB and EuCOB emitted respectively very bright green (543 nm) and red (611 nm) light, indicating that they are promising new phosphors. It is noteworthy that we could detect a remarkably strong red emitting region in the EuCOB-ScCOB-PrCOB ternary composition spread library.(C) 2003 Elsevier B.V. All rights reserved.