Patent ID: 7160614

Claim:
A complex material composed of crystalline superfine particles having a grain size in the range from 5 nm to 100 nm and the surface thereof is covered by surfactant and another material, and emitting light depending upon the time-rate-of-change of a stress applied thereto, wherein the crystalline superfine particle has a composition expressed by the general formula A x B y O z where 0.8≦x≦1.1 1.8≦y≦2.2 {(2x+3y)/2}−0.2<z<{(2x+3y)/2}+0.2 A=Sr k Ba j Ca m Mg n (0≦k,l,m,n≦1, k+l+m+n=1) B=Al l−p Dp (0≦p<1) D=Y q Ga r In t (0≦q,r,t≦1,q+r+t=1) wherein a rare earth element or a transition metal element is added by 0.2 mol or less in total relative to 1 mol of A x B y O z , wherein weight percent of the crystalline superfine particles is from 30% to 80%.