RD-ZD-25F, 220V/50W motor as a generator
Your motor is a permanent magnet DC type so yes, you can use it as a generator. 

The permanent magnets create a fixed field strength. Since the voltage generated in a wire is proportional to its rate of movement through the magnetic field, the motor will produce higher voltage at higher rpm. To get constant voltage out you have two options:-


Spin the motor at constant rpm. 


Depending on what mechanism is driving it you may be able to use a centrifugal governor, CVT or variable pitch blades to adjust the speed.   


Regulate the output down to a lower voltage.   


You could try using a switched mode power supply that is designed for eg. 90~230V input and 12V output.