We have grown neodymium-doped mixed apatite crystals [(Sr1-xBax)(5)(PO4)(3)
F, Sr-5(P1-xVxO4)(3)F, and Ba-5(P1-xVxO4)(3)F] and spectroscopically studie
d them as potential gain media for a laser source for atmospheric water sen
sing operating at 944.11 nm. We conclude that an appropriate apatite host m
aterial for a 914.11-nm laser should be a mixture of Sr-5(PO4)(3)F With a s
mall fraction of Ba-5(PO4)(3)F. Precise wavelength tuning around 944.11 nm
can be accomplished by varying the host composition, temperature, and thres
hold population inversion. In apatite crystals of mixed composition, the am
plified spontaneous emission (ASE) loss at 1.06 mum is predicted to be sign
ificantly smaller than that in the end members.