Concerned Eu: you can find Eu energy levels and some references at Marwin J. Weber "Handbook of Lasers".  I can send  this book (PDF) to your E-mail.

These results were obtained long ago. Eu laser generation was very weak and nobody study this problem again later.

hi, I think you can easily find the information in solid state laser reference book. for reference book, I'll recommend you to refer "solid state laser" by W. Koechner.

in short, host material will determine the physical and thermal properties of the laser crystal. 

u can refer to "solid state laser engineering by W.Koechner". 6th revised and updated edition page 48 and page 54 Host material influences physical, chemical, thermal and mechanical  properties, fluorescent line widths optical qualities etc.