A system and method measures subterranean stress. The system and method includes a cement mixture that is mixed with water to set as a solid and a stress measuring-medium having piezospectroscopic properties that directly reveals stress in situ within the cement mixture in response to a photo stimulation. The stress measuring-medium combines with the cement mixture as a dry blend before being combined with water.

An oxide fluorescent material has a composition represented by the following formula (1):

(Mg.sub.1-pM.sup.1.sub.p).sub.q(Li.sub.1-rM.sup.2.sub.r).sub.s(In.sub.1-tM.sup.3.sub.t).sub.u(Ge.sub.1-vM.sup.4.sub.v).sub.wOx:Cr.sub.y,M.sup.5.sub.z(1) wherein M.sup.1 represents at least one element selected from the group consisting of Ca, Sr, Ba, and Zn; M.sup.2 represents at least one element selected from the group consisting of Na, K, Rb, and Cs; M.sup.3 represents at least one element selected from the group consisting of Al, Ga, and Sc; M.sup.4 represents at least one element selected from the group consisting of Si, Ti, Zr, Sn, and Hf; M.sup.5 represents at least one element selected from the group consisting of Ni, Ce, Eu, Fe, Mn, Nd, Tm, Ho, Er, and Yb; and p, q, r, s, t, u, v, w, x, y, and z satisfy 0p1.0, 0.1q0.9, 0r1.0, 0.05s0.45, 0t0.5, 0.05u0.45, 0v1.0, 0.8w1.3, 2.6x3.6, 0.002y0.5, 0z0.3, and 0.9q+s+u1.2.

A light emitting device includes a light emitting diode chip configured to emit first light having a peak wavelength of 400 nm to 470 nm; a wavelength conversion material converting a portion of the first light into second light having a peak wavelength of 620 nm to 670 nm; and a near-infrared phosphor configured to convert a portion of the first light into third light having a peak wavelength of 740 nm to 820 nm, wherein the near-infrared phosphor includes a phosphor represented by composition formula CaAl.sub.(12-x-y)Ga.sub.yO.sub.19:xCr.sup.3+, where x satisfies 0.1x0.3 and y satisfies 1 or more, and an emission spectrum of the third light alone has a ratio of an intensity of 690 nm relative to an intensity of 780 nm of 0.3 or less.

An oxide fluorescent material has a composition represented by the following formula (1).

(Ga.sub.1-uM.sup.1.sub.u).sub.2(Ge.sub.1-vM.sup.2.sub.v).sub.wO.sub.x:Cr.sub.y,M.sup.3.sub.z(1), wherein M.sup.1 represents at least one element selected from the group consisting of Al, Sc, and In; M.sup.2 represents at least one element selected from the group consisting of Si, Ti, Zr, Sn, and Hf, M.sup.3 represents at least one element selected from the group consisting of Ni, Eu, Fe, Mn, Nd, Tm, Ho, Er, and Yb; and u, v, w, x, y, and z satisfy 0u1.0, 0v0.5, 1.0w3.0, 5x9, 0.005y1.0, and 0z0.5, respectively.

This specification discloses spinel-type phosphors that may be advantageously employed in light sources for medical optical coherence tomography (OCT), light sources for medical OCT comprising such phosphors, and OCT systems comprising such light sources.

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.

An oxide phosphor includes phosphor particles containing a host crystal containing Ga and oxygen and an activating element, and a first compound particle disposed on at a surface(s) of the phosphor particles, the at least one first compound particle containing an oxide particle containing a first element selected from the group consisting of Group 4 elements, Group 5 elements, Group 14 elements, and Group 15 elements.

To provide an oxide fluorescent material that has a light emission peak wavelength in a wavelength range of from red light to near infrared light. The oxide fluorescent material has a composition encompassed in a compositional formula represented by the following formula (1):
(Li.sub.1-tM.sup.1.sub.t).sub.u(Ga.sub.1-vM.sup.2.sub.v).sub.5O.sub.w:Cr.sub.x,Ni.sub.y,M.sup.3.sub.z,(1) wherein in the formula (1), M.sup.1 represents at least one kind of an element selected from the group consisting of Na, K, Rb, and Cs; M.sup.2 represents at least one kind of an element selected from the group consisting of B, Al, Sc, In, and a rare earth element; M.sup.3 represents at least one kind of an element selected from the group consisting of Si, Ge, Sn, Ti, Zr, Hf, Bi, V, Nb, and Ta; and t, u, v, w, x, y, and z each satisfy 0t1.0, 0.7u1.6, 0v<1.0, 7.85w11.5, 0.05x1.2, 0y0.5, 0.25

An oxide phosphor has a composition represented by the following formula (1).

##STR00001##

wherein M.sup.1 represents one or more selected from Na, K, Rb, and Cs, M.sup.2 represents one or more selected from Mg, Ca, Sr, and Ba, M.sup.3 represents one or more selected from Al, Sc, and In, M.sup.4 represents one or more selected from Si, Ti, Zr, Sn, and Hf, M.sup.5 represents one or more selected from Ni, Ce, Eu, Fe, Mn, Nd, Tm, Ho, Er, and Yb, 0q0.5, 0r1.0 0s4.0, 0t1.0, 5u10, 0v1.0, 0.5w5.0, 10x30, and y and z satisfy 0.02y0.5, 0z0.3, and y>z.

An oxide fluorescent material comprises: at least one first element M.sup.1 selected from Li, Na, K, Rb, and Cs; at least one second element M.sup.2 selected from Mg, Ca, Sr, Ba, and Zn; at least one third element M.sup.3 selected from B, Al, Ga, In, and rare earth elements; at least one fourth element M.sup.4 selected from Si, Ti, Ge, Zr, Sn, Hf, and Pb; O; and Cr, wherein when the molar ratio of the at least one fourth element M.sup.4 in 1 mol of the composition is 5, the molar ratio of the at least one first element M.sup.1 is 0.7 or more and 1.3 or less, the molar ratio of the at least one second element M.sup.2 is 1.5 or more and 2.5 or less, the molar ratio of the at least one third element M.sup.3 is 0.7 or more and 1.3 or less, the molar ratio of oxygen is 12.9 or more and 15.1 or less, and the molar ratio of Cr is more than 0 and 0.2 or less, and wherein the oxide fluorescent material has a light emission peak wavelength in a range of 700 nm or more and 1,050 nm or less in a light emission spectrum of the oxide fluorescent material.