Driving blue LED with 3.3V using an op-amp
LM318 is only specified to drive to within 3v of either rail, it's not a rail to rail (R2R) output opamp. As you've got it supplied from the +5v pin, its output current into a 3v load will be low at best, and might be zero.

For a drop in replacement, find an amplifier that's got a R2R output.

It might be simpler to use a switch instead, a simple transistor or FET, or a 5v rail gate with 3.3v capable input like an HCT74xx part. LM339 makes a nice low current FET driver as well, output pulls close to ground, and the inputs are very flexible.