A laser medium includes a single crystal of Cr4+:Mg2-xMxSi1-yAyO4, where, where M is a bivalent ion having an ionic radius larger than Mg2+, and A is a tetravalent ion having an ionic radius larger than Si4+. In addition, either a) 0≦x<2 and 0<y<1 or b) 0<x<2 and y is 0 or 1 with the proviso that if M is Ca2+ and x=1 then y is not 0. The laser medium can be used in a laser device, such as a tunable near infrared (NIR) laser.