I have the following JSON string, which was an Objective C array then encoded to JSON:
$jsonString=[\\\"a@gmail.com\\\",\\\"b@gmail.com\\\",\\\"c@gmail.com\
Assuming the lack of quotes around your JSON in the question is a transposition error during posting, then the code you're using is fine: http://codepad.org/RWEYM42x
You do need to ensure your string is UTF8 encoded. You can use the built in encoder if it isn't ( http://php.net/manual/en/function.utf8-encode.php ).
For any further help, you need to actually tell us what you are getting with your code.