Is Frequency Quantized in Quantum Mechanics?

[=SJ=]

As to E=hf I understand that a energy can be arbitrary in order of proportional packages to given frequency. But is there any equation in quantum mechanics which imply a freq to be quantized?
Thanks a lot!

 

[Nugatory]

If $E$ can only take on discrete values, then $E=hf$ obviously implies that $f$ can only take on discrete values as well.

However, whether $E$ is limited to discrete values or not depends on the system. For example, a bound electron is limited that way but an unbound one is not.