Current too low at forward voltage of power led
The Cree spec shows 2.9 - 3.5 V for 700 mA



You should be able to engineer a current controller that works at 5 V without any problems.
Perhaps something simple like this, though it will have a thermal variation of current which can be reduce by putting the NPN close the LED.







simulate this circuit &ndash; Schematic created using CircuitLab