Disclosed are a phosphor sheet capable of improving color purity of each of RGB reproduced through a color filter, a white light source device including the phosphor sheet, and a display device including the white light source device. The disclosed phosphor sheet is a phosphor sheet for converting LED light into white light, including: a phosphor layer containing at least a phosphor and a resin; and a pair of transparent substrates sandwiching the phosphor layer, in which the phosphor sheet includes a coloring material having an absorption maximum wavelength of at least one of from 480 nm to 510 nm or from 570 nm to 620 nm.

A light source using a wavelength conversion member is increased in brightness. A wavelength conversion element 11 includes a plurality of wavelength conversion members 12 bundled together, each containing a dispersion medium and phosphor powder dispersed in the dispersion medium.

A light source using a wavelength conversion member is increased in brightness. A wavelength conversion element 11 includes a plurality of wavelength conversion members 12 bundled together, each containing a dispersion medium and phosphor powder dispersed in the dispersion medium.

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.

A light source using a wavelength conversion member is increased in brightness. A wavelength conversion element 11 includes a plurality of wavelength conversion members 12 bundled together, each containing a dispersion medium and phosphor powder dispersed in the dispersion medium.