What emperor used the name between 1804 and 1813 ?
It was used as an official name by Emperor Gia Long in 1804-1813 . < / ref > The use of " Vietnam " was revived in modern times by nationalists including Phan Bội Châu , whose book " Việt Nam vong quốc sử " ( History of the Loss of Vietnam ) was published in 1906 .