The present invention provides a single crystal heat treatment method, having a step of heating a single crystal of a cerium-doped silicate compound represented by any of general formulas (1) to (4) below in an oxygen-containing atmosphere Y.sub.2-(x+y)Ln.sub.xCe.sub.ySiO.sub.5 (1) (wherein Ln represents at least one elemental species selected from a group consisting of elements belonging to the rare earth elements, x represents a numerical value from 0 to 2, and y represents a numerical value greater than 0 but less than or equal to 0.2) Gd.sub.2-(z+w)Ln.sub.zCe.sub.wSiO.sub.5 (2) (wherein Ln represents at least one elemental species selected from a group consisting of elements belonging to the rare earth elements, z represents a numerical value greater than 0 but less than or equal to 2, and w represents a numerical value greater than 0 but less than or equal to 0.2) Gd.sub.2-(p+q)Ln.sub.pCe.sub.qSiO.sub.5 (3) (wherein Ln represents at least one elemental species selected from a group consisting of Dy, Ho, Er, Tm, Yb, Lu, Y and Sc, which are rare earth elements having an ionic radius smaller than Tb, p represents a numerical value greater than 0 but less than or equal to 2, and q represents a numerical value greater than 0 but less than or equal to 0.2) Gd.sub.2-(r+s)Lu.sub.rCe.sub.sSiO.sub.5 (4) (wherein r represents a numerical value greater than 0 but less than or equal to 2, and s represents a numerical value greater than 0 but less than or equal to 0.2).