To Whom It May Be Concern: (it is not polite, i think Dear sir or madam is ok)
As the Chief of National Key Laboratory of Composite Technology in Extreme Environments, I have had the pleasure of knowing XXX for his great performance in research in ( for is better, because you use"have had") the last two years when he was a master student in our center.
He has been a tremendous student and an asset to our center. I would like to take this opportunity to recommend XXX for your Ph.D. program.
I feel confident that he will continue to succeed in his further studies. Mr.X is a dedicated and hard-working student and has been admired by other people for his wide range of courses in a variety of fields to study.( maybe there is some wrong) In master courses, he is self-motivated and has achieved exceptional academic performance. Two of the top Graduate Fellowships are the direct results of his hard work in courses and innovations in research have brought him the Johnson Electric Special Scholarship.
Mr.X has also assisted us in our research projects. She (or he? you use she in the second paragragh) has successfully demonstrated leadership ability and talented solutions in the research activities. He often coordinated projects involving numerous people, and his ability to work collaboratively while guiding the project quickly and effectively was outstanding.(
As I know, he has developed a kind of data analysis software which simplifies and increases the efficiency of our teamwork. His advice has been a great help to other researchers, many of whom have taken time to share their comments with me regarding his pleasant and encouraging attitude.