Long persistent phosphorescence phosphor

A long persistent phosphorescence phosphor comprising:

• i) a europium-activated long persistent phosphorescence silicate phosphor of the formula (I),
• m(Sr.sub.1-a M.sup.1.sub.a)O.multidot.n(Mg.sub.1-b M.sup.2.sub.b)O.multidot.2(Si.sub.1-c Ge.sub.c)O.sub.2 :
• Eu.sub.x Ln.sub.y (I)
• wherein M.sup.1 is Ba, M.sup.2 is at least one element selected from the group consisting of Be, Zn and Cd, Ln is at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, B, Al, Ga, In, Tl, Sb, Bi, As, P, Sn, Pb, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cr and Mn, m(Sr.sub.1-a M.sup.1.sub.a)O.multidot.n(Mg.sub.1-b M.sup.2.sub.b)O.multidot.2(Si.sub.1-c Ge.sub.c)O.sub.2 being a host material for the phosphor, Eu serving as an activator, and Ln serving as a coactivator,
• wherein
• 0.ltoreq.a.ltoreq.0.8,
• 0.ltoreq.b.ltoreq.0.2,
• 0.ltoreq.c.ltoreq.0.2,
• 1.5.ltoreq.m.ltoreq.3.5,
• 0.5.ltoreq.n.ltoreq.1.5,
• 1.times.10.sup.-5 .ltoreq.x.ltoreq.1.times.10.sup.-1 (g.multidot.atm per mole of the host material),
• 1.times.10.sup.-5 .ltoreq.y.ltoreq.1.times.10.sup.-1 (g.multidot.atm per mole of the host material),
• comprising at least one halogen atom selected from the group consisting of F, Cl, Br and I in an amount of 1.times.10.sub.-5 to 1.times.10.sub.-1 g.multidot.atm per mole of the host material;
• and
• ii) an organic fluorescent pigment which is deposited on the surface of said europium-activated long persistent silicate phosphor.