Is a jury allowed to consider "other crimes" evidence at the penalty phase?

Defendant argues that the trial court committed prejudicial error because it failed to discharge its sua sponte duty to instruct the jury, at the penalty phase, that the jury could not consider "other crimes" evidence as aggravating circumstances unless it first found those crimes were proven beyond a reasonable doubt. (See, e.g., People v. Robertson (1982) 33 Cal.3d 21, 53-55, 188 Cal.Rptr. 77, 655 P.2d 279.) Specifically, defendant argues that the prosecutor, in his case-in-chief at the guilt phase, introduced "other crimes" evidence of defendant's gun possession and the fact defendant may have also raped the three victims. Thus, the court's failure to give this instruction requires reversal. This contention is without merit.