Amorphous silicon carbide may be doped with one or more ions such as vanadium and these ions may radiate light if excited, for example, using optical or electrical pumping. A single photon light source may be formed from a single such ion that is pumped or from a plurality of ions that are pumped if light from only one ion is collected, e.g., using an aperture or pin hole. Such single photon sources may possibly be use in quantum computing, quantum sensing and/or quantum telecommunications.

Amorphous silicon carbide may be doped with one or more ions such as vanadium and these ions may radiate light if excited, for example, using optical or electrical pumping. A single photon light source may be formed from a single such ion that is pumped or from a plurality of ions that are pumped if light from only one ion is collected, e.g., using an aperture or pin hole. Such single photon sources may possibly be use in quantum computing, quantum sensing and/or quantum telecommunications.

Provided is a photochromic substance that has lower toxicity, exhibits good sensitivity in a visible light region, changes color deeply, has slow speed of color fading, has chemical and thermal stability, and has good durability. The photochromic substance has a composition represented by the formula:
Ba.sub.(a-b)Ca.sub.bMg.sub.cSi.sub.dO.sub.e:Fe.sub.fM.sub.gM.sub.h where 1.8a2.2, 0b0.1, 1.4c3.5, 1.8d2.2, e=(a+c+2d), 0.0001f, 0.0001g, 0h, M is at least one of Al and Eu, and M is at least one element selected from the group consisting of Na, K, Nd, Li, S, C, Ti, V, Mn, Cr, Cu, Ni, Co, Ge, Zn, Ga, Zr, Y, Nb, In, Ag, Mo, Sn, Sb, Bi, Ta, W, La, Ce, Pr, Nd, Sm, Gd, Er, Ho, Tb, Tm, Yb, Lu, P, Cd, and Pb.