Rotate gameobject on Y axis

Hey all. I am trying to rotate a gameobject (in this case, a door) by 90 degrees in its Y axis when the player enter the sphere collider around the door, basically opening the door.

using UnityEngine;
using System.Collections;

public class DoorOpen : MonoBehaviour 
{
	private GameObject player;

	void Awake() 
	{
		player = GameObject.FindGameObjectWithTag("Player");
	}

	void OnTriggerEnter (Collider other)
	{
		if(other.gameObject == player)
		{
			transform.Rotate.y(0,90,0);
		}
	}
}

Here I tried transform.Rotate.y but getting an error. I can’t seem to find the correct way to format the code to simply rotate. On a side note, not entirely necessary, but is there also a way to slow the rotation down, instead of making it happen in a single frame, to better simulate the opening of a door?

You can make the movement occur over multiple frames by using Vector3.lerp() or Vector3.slerp, but as previously stated an animation is probably the better solution.