If the bulb is quoted as "dimmable" in its specification, you need to use phase control dimming. So get back to your zero-crossing detector and Triac controller with opto-isolators.
Deva_Rishi:
Now does anyone think PWM dimming will work in between then extra rectifier bridge and the bulb ?
Possibly. At 500 Hz it might work, no faster. Now what are you going to use to switch it? Phase control with a TRIAC would likely be much easier.
And your Subject heading is misleading. It is a 220 V bulb.