He is a very bright and qualified individual, and a pleasure to work with. Indicate that you're interested in a telephone interview and when you're available for a face-to-face interview. Draft an introduction that gives a brief statement about your interest in the job, where you saw it advertised and your qualifications.
I believe that Bill would be an asset to your department, as he brings a tremendous amount of energy and enthusiasm to his studies. State this briefly, without an accusatory tone.
For example, write: "I reduced purchasing costs by 20 percent each year during my five-year career with ABC Retail. During the two years I worked with her, she was personally responsible for adding several new clients in Asia and Africa.
Express your appreciation for the reader's time and favorable consideration of your interest and qualifications. If you know the name of the department -- but not the addressee's name -- include that above the company name. Follow your contact information with the date of your letter.
Describe your qualifications and background in a short paragraph -- two or three sentences. Include significant accomplishments, such as measurable cost savings or increased productivity. If necessary, use more than one paragraph to provide details.
When I worked with her at XYZ, I was impressed by her ability to communicate the effectiveness of our products to our clients and close a sale.