1. Patent Search
  2. Details

RED-LUMINESCENT PHOSPHOR WITH LONG AFTERGLOW AND FABRICATION METHOD THEREOF

20230090990 · 2023-03-23

    Inventors

    Cpc classification

    International classification

    Abstract

    A red-luminescent long-afterglow phosphor, represented by Mg.sub.xZn.sub.yGe.sub.zO.sub.3: aMn.sup.2+, bEu.sup.3+, cR.sup.3+. The phosphor is a kind of oxide compound based white powder. The phosphor powder synthesis process is environmentally friendly, no sintering-assisted gas required and no harmful gas generated during or after sintering. The phosphor powder can be excited by UV and is chemically stable.

    Claims

    1. A phosphor having a chemical formula: Mg.sub.xZn.sub.yGe.sub.zO.sub.3: aMn.sup.2+, bEu.sup.3+, cR.sup.3+, wherein R is an element selected from the group consisting of erbium (Er), thulium (Tm), holmium (Ho), samarium (Sm), praseodymium (Pr), ytterbium (Yb) and neodymium (Nd); Mg.sub.xZn.sub.yGe.sub.zO.sub.3 is a host material; and x, y, z, a, b and c are each independently a positive number, wherein a is a molar ratio of Mn.sup.2+ to the host material, b is a molar ratio of Eu.sup.3+ to the host material, and c is a molar ratio of R.sup.3+ to the host material.

    2. The phosphor according to claim 1, wherein 0.95 ≤ x + y ≤ 0.99, 0.3 ≤ x ≤ 0.7.

    3. The phosphor according to claim 1, wherein 1.00 ≤ z ≤ 1.5.

    4. The phosphor according to claim 1, wherein 0.0001 ≤ a ≤ 0.02.

    5. The phosphor according to claim 1, wherein 0.0001 ≤ b ≤ 0.05.

    6. The phosphor according to claim 1, wherein 0.0001 ≤ c ≤ 0.005.

    7. The phosphor according to claim 1, wherein c < b, wherein b is at least 2 times greater than c.

    8. The phosphor according to claim 1, wherein 0.95 ≤ x + y ≤ 0.99, 0.3 ≤ x ≤ 0.7, 1.0 ≤ z ≤ 1.5, 0.0001 ≤ a ≤ 0.02, 0.0001 ≤ b ≤ 0.05, 0.0001 ≤ c ≤ 0.005, c < b, wherein b is at least 2 times greater than c.

    9. The phosphor according to claim 1, wherein R is Tm, 0.50 ≤ x ≤ 0.60, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.003, 0.006 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    10. The phosphor according to claim 1, wherein R is Tm, 0.35 ≤ x ≤ 0.42, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.005 ≤ a ≤ 0.02, 0.002 ≤ b ≤ 0.008, 0.0002 ≤ c ≤ 0.001.

    11. The phosphor according to claim 1, wherein R is Er, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    12. The phosphor according to claim 1, wherein R is Ho, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    13. The phosphor according to claim 1, wherein R is Pr, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    14. The phosphor according to claim 1, wherein R is Nd, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    15. The phosphor according to claim 1, wherein R is Sm, 0.35 ≤ x ≤ 0.50, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.002 ≤ b ≤ 0.01, 0.0001 ≤ c ≤ 0.002.

    16. The phosphor according to claim 1, wherein R is Yb, 0.35 ≤ x ≤ 0.50, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.0002 ≤ b ≤ 0.01, 0.0001 ≤ c ≤ 0.001.

    17. The phosphor according to claim 1, wherein the phosphor is a powder.

    18. The phosphor according to claim 1, wherein the phosphor has an emission peak between 650-700 nm.

    19. The phosphor according to claim 1, wherein the phosphor has an emission peak between 670-690 nm.

    20. A method of preparing the phosphor according to claim 1, the method comprising: contacting a Mg.sup.2+ salt, a Zn.sup.2+ salt, GeO.sub.2, a Mn.sup.2+ salt, Eu.sub.2O.sub.3, and a metal oxide selected from the group consisting of Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Ho.sub.2O.sub.3, Sm.sub.2O.sub.3, Pr.sub.6O.sub.11, Yb.sub.2O.sub.3 and Nd.sub.2O.sub.3, wherein each of the Mg.sup.2+ salt and the Zn.sup.2+ salt is independently an oxide, hydroxide, or carbonate salt; and the Mn.sup.2+ salt is an oxide or carbonate salt; thereby forming a mixture; and sintering the mixture thereby forming the phosphor.

    Description

    BRIEF DESCRIPTION OF DRAWINGS

    [0032] The appended drawings, where like reference numerals refer to identical or functionally similar elements, contain figures of certain embodiments to further illustrate and clarify the above and other aspects, advantages and features of the present invention. It will be appreciated that these drawings depict embodiments of the invention and are not intended to limit its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

    [0033] FIG. 1 shows a X-ray diffraction spectrum refers to Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+ according to Example 1;

    [0034] FIG. 2 shows excitation and emission spectra of a comparative phosphor Mg.sub.0.4977Zn.sub.0.5GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+;

    [0035] FIG. 3 shows excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+;

    [0036] FIG. 4 shows afterglow duration of the prior art phosphor and Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, based on the testing standard of DIN 67510-1;

    [0037] FIG. 5 shows afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, after excitation by 16 W 308 nm UV light source for 5 min;

    [0038] FIG. 6 shows excitation and emission spectra of Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+ according to Example 2;

    [0039] FIG. 7 shows afterglow duration of the prior art phosphor and Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+, based on the testing standard of DIN 67510-1;

    [0040] FIG. 8 shows excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43GeO.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+ according to Example 3;

    [0041] FIG. 9 shows afterglow duration of Mg.sub.0.56Zn.sub.0.43GeO.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, based on the testing standard of DIN 67510-1;

    [0042] FIG. 10 shows excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Er.sup.3+ according to Example 4;

    [0043] FIG. 11 shows afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Er.sup.3+, based on the testing standard of DIN 67510-1;

    [0044] FIG. 12 shows excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Ho.sup.3+ according to Example 5;

    [0045] FIG. 13 shows afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Ho.sup.3+, based on the testing standard of DIN 67510-1;

    [0046] FIG. 14 shows excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Pr.sup.3+ according to Example 6;

    [0047] FIG. 15 shows afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Pr.sup.3+, based on the testing standard of DIN 67510-1;

    [0048] FIG. 16 shows excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Nd.sup.3+ according to Example 7;

    [0049] FIG. 17 shows afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Nd.sup.3+, based on the testing standard of DIN 67510-1;

    [0050] FIG. 18 shows excitation and emission spectra of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.003Eu.sup.3+, 0.001Sm.sup.3+ according to Example 8;

    [0051] FIG. 19 shows afterglow duration of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.003Eu.sup.3+, 0.001Sm.sup.3+, based on the testing standard of DIN 67510-1;

    [0052] FIG. 20 shows excitation and emission spectra of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+, 0.0003Yb.sup.3+ according to Example 9; and

    [0053] FIG. 21 shows afterglow duration of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+, 0.0003Yb.sup.3+, based on the testing standard of DIN 67510-1.

    DETAILED DESCRIPTION

    [0054] The present disclosure discloses a red-luminescent long-afterglow phosphor. The synthesis of red-luminescent long-afterglow phosphor is described in different embodiments of the present disclosure.

    [0055] The present disclosure provides a phosphor having a chemical formula: Mg.sub.xZn.sub.yGe.sub.zO.sub.3: aMn.sup.2+, bEu.sup.3+, cR.sup.3+, wherein R is an element selected from the group consisting of erbium (Er), thulium (Tm), holmium (Ho), samarium (Sm), praseodymium (Pr), ytterbium (Yb) and neodymium (Nd); Mg.sub.xZn.sub.yGe.sub.zO.sub.3 is a host material; and x, y, z, a, b and c are each independently positive numbers, wherein a is a molar ratio of Mn.sup.2+ to the host material, b is a molar ratio of Eu.sup.3+ to the host material, and c is a molar ratio of R.sup.3+ to the host material.

    [0056] In certain embodiments, 0.95 ≤ x + y ≤ 0.99, 0.3 ≤ x ≤ 0.7.

    [0057] In certain embodiments, 1.00 ≤ z ≤ 1.5 or 1.05 ≤ z ≤ 1.5.

    [0058] In certain embodiments, 0.0001 ≤ a ≤ 0.02 or 0.0001 ≤ a ≤ 0.005.

    [0059] In certain embodiments, 0.0001 ≤ b ≤ 0.05.

    [0060] In certain embodiments, 0.0001 ≤ c ≤ 0.005.

    [0061] In certain embodiments, c < b, wherein b is at least 2 times greater, 3 times greater, 4 times greater, or 5 times greater than c. In certain embodiments, b is between 2-10 greater, 3-10 greater, or 3-5 greater than c.

    [0062] In certain embodiments, 0.95 ≤ x + y ≤ 0.99, 0.3 ≤ x ≤ 0.7, 1.0 ≤ z ≤ 1.5, 0.0001 ≤ a < 0.02, 0.0001 ≤ b ≤ 0.05, 0.0001 ≤ c ≤ 0.005, c < b, wherein b is at least 2 times greater than c.

    [0063] In certain embodiments, R is Tm, 0.50 ≤ x ≤ 0.60, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.003, 0.006 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001 or 0.50 ≤ x ≤ 0.60, 0.95 ≤ x + y ≤ 0.99, 1.1 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.003, 0.006 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    [0064] In certain embodiments, R is Tm, 0.35 ≤ x ≤ 0.42, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.005 ≤ a ≤ 0.02, 0.002 ≤ b ≤ 0.008, 0.0002 ≤ c ≤ 0.001 or 0.35 ≤ x ≤ 0.42, 0.95 ≤ x + y ≤ 0.99, 1.1 ≤ z ≤ 1.3, 0.005 ≤ a ≤ 0.02, 0.002 ≤ b ≤ 0.008, 0.0002 ≤ c ≤ 0.001.

    [0065] In certain embodiments, R is Er, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001 or 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.1 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    [0066] In certain embodiments, R is Ho, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001 or 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.1 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    [0067] In certain embodiments, R is Pr, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001 or 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.1 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    [0068] In certain embodiments, R is Nd, 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001 or 0.35 ≤ x ≤ 0.57, 0.95 ≤ x + y ≤ 0.99, 1.1 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.005 ≤ b ≤ 0.01, 0.0002 ≤ c ≤ 0.001.

    [0069] In certain embodiments, R is Sm, 0.35 ≤ x ≤ 0.50, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.002 ≤ b ≤ 0.01, 0.0001 ≤ c ≤ 0.002.

    [0070] In certain embodiments, R is Yb, 0.35 ≤ x ≤ 0.50, 0.95 ≤ x + y ≤ 0.99, 1.0 ≤ z ≤ 1.3, 0.001 ≤ a ≤ 0.008, 0.0002 ≤ b ≤ 0.01, 0.0001 ≤ c ≤ 0.001.

    [0071] In certain embodiments, phosphor has an emission peak between 620-750 nm, 620-730 nm, 620-710 nm, 630-700 nm, 640-700 nm, 650-700 nm, 660-700 nm, 670-690 nm, or 680 nm.

    [0072] In certain embodiments, the following raw materials serve as starting materials in a sintering fabrication. To compose the host, the oxides, hydroxides and carbonates of Mg.sup.2+ and Zn.sup.2+ may be utilized. To serve as an activator and a sensitizer, which are dopants, the oxides, MnO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Ho.sub.2O.sub.3, Sm.sub.2O.sub.3, Pr.sub.6O.sub.11, Yb.sub.2O.sub.3 and Nd.sub.2O.sub.3 can be selected. For Mn.sup.2+, instead of oxide, carbonate may be selected. The starting materials of red-luminescent long-afterglow phosphor are not limited to oxides, hydroxides and carbonates.

    [0073] In certain embodiments, the phosphor is prepared according to a method comprising: contacting a Mg.sup.2+ salt, a Zn.sup.2+ salt, GeO.sub.2, a Mn.sup.2+ salt, Eu.sub.2O.sub.3, and a metal oxide selected from the group consisting of Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Ho.sub.2O.sub.3, Sm.sub.2O.sub.3, Pr.sub.6O.sub.11, Yb.sub.2O.sub.3 and Nd.sub.2O.sub.3, wherein each of the Mg.sup.2+ salt and the Zn.sup.2+ salt is independently an oxide, hydroxide, or carbonate salt; and the Mn.sup.2+ salt is an oxide or carbonate salt; thereby forming a mixture; and sintering the mixture thereby forming the phosphor. In certain embodiments, the mixture is sintered in the presence of oxygen. In certain embodiments, the mixture is air sintered. In certain embodiments, the metals are combined in any stoichiometry described herein.

    [0074] The starting materials are weighted according to the desired molar ratios, and then they are sufficiently wet mixed by a ball milling mixer with solvent such as ethanol. The sufficiently mixed starting materials with solvent are then transferred into a container and baked in an oven at a certain temperature according to the volatilization temperature of the solvent. For example, if using ethanol as solvent, the baking temperature can be set as 80° C. The baking process is to remove all the solvent and then obtain sufficiently mixed starting materials.

    [0075] The above mixed starting materials are then sieved to decrease their stacking density. In other words, the purpose of sieving is to make the starting materials looser among each other, which favors efficient heat conduction and sintering.

    [0076] The sufficiently sieved and mixed starting materials are put in a heat-resistant container such as aluminum oxide crucible or quartz crucible. Then, they are placed into a furnace and sintered at a temperature ranging from 1100° C. to 1350° C., holding for several minutes to hours in air atmosphere.

    [0077] After cooling down, the sintered powder is ground to a fine powder and the red-luminescent long-afterglow phosphor is finally obtained.

    [0078] The long-persistent-luminescent phosphor powder represented by Mg.sub.xZn.sub.yGe.sub.zO.sub.3: aMn.sup.2+, bEu.sup.3+, cR.sup.3+, wherein R is an element selected from the group consisting of erbium (Er), thulium (Tm), holmium (Ho), samarium (Sm), praseodymium (Pr) ytterbium (Yb) and neodymium (Nd). The red-luminescent phosphor powder is synthesized by doping manganese (Mn) ions, europium (Eu) ions and R ions into host crystal of Mg.sub.xZn.sub.yGe.sub.zO.sub.3. Mn.sup.2+ serves as activator, while Eu.sup.3+ serves as first sensitizer and R.sup.3+ serves as second sensitizer.

    [0079] In certain embodiments, x+y is smaller than 0.99 in the formula of Mg.sub.xZn.sub.yGe.sub.zO.sub.3: aMn.sup.2+, bEu.sup.3+, cR.sup.3+. The non-stoichiometry can induce trap states to improve afterglow duration.

    [0080] In certain embodiments, the x for Mg is ranging from 0.3 to 0.7.

    [0081] In certain embodiments, the starting material of Mg is Mg(OH).sub.2, which is active in high temperature sintering, contributing longer afterglow.

    [0082] In certain embodiments, the starting material of Zn is ZnO. Zn(OH).sub.2 may deteriorate the afterglow performance.

    [0083] In certain embodiments, the molar ratio of germanium (Ge) is in excess. A low stoichiometry ratio of Ge may lead to a green florescence with a peak of 530 nm, plus red florescence and red afterglow with a peak of 680 nm. The excess molar amount of Ge can range from 5% to 50%. With increasing the molar amount of Ge, the peak of green florescence weakens and finally vanish.

    [0084] In certain embodiments, the starting material of Mn is MnO. The molar ratio of Mn.sup.2+ to the host material can range from 0.0001 to 0.02. Mn.sup.2+ serves as activation center in Mg.sub.xZn.sub.yGe.sub.zO.sub.3 crystal cell. Lower concentration of Mn.sup.2+ contributes limited amount of activation center and leads to incomplete luminescence, while higher concentration of Mn.sup.2+ can result in concentration quenching effect thus deteriorate afterglow performance.

    [0085] In certain embodiments, the molar ratio of Eu.sup.3+ to the host material ranges from 0.0001 to 0.05. As first co-dopant and first sensitizer to the dopant and activator of Mn.sup.2+, with adding of Eu.sup.3+, afterglow performance can improve significantly.

    [0086] In certain embodiments, the molar ratio of R.sup.3+ to the host material ranges from 0.0001 to 0.005. As second co-dopant and second sensitizer to the dopant and activator of Mn.sup.2+, the molar ratio of R.sup.3+ is generally smaller than the molar ratio of Eu.sup.3+ (e.g., about 3-10 times smaller), in case of concentration quenching effect happening. After adding second co-dopant, afterglow duration further improves.

    [0087] In certain embodiments, depending on the generated shallow trap states within the host bandgap, the dopant element is Tm.

    [0088] In certain embodiments, depending on the certain molar ratio of Mg and Zn (e.g., 0.35 ≤ x ≤ 0.42, 0.95 ≤ x + y ≤ 0.99), the photoluminescence excitation range broadens from UV to visible light.

    [0089] In certain embodiments, depending on the certain molar ratio of Mg and Zn (e.g., 0.35 ≤ x ≤ 0.42, 0.95 ≤ x + y ≤ 0.99), the initial afterglow intensity enhanced to more than 10 times.

    [0090] In certain embodiments, depending on the certain molar ratio of Mg and Zn (e.g., 0.50 ≤ x ≤ 0.60, 0.95 ≤ x + y ≤ 0.99), as well as the generated shallow trap states, the afterglow duration extends to 80 min.

    Example 1

    [0091] Based on the formula of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, the following starting materials were weighted: 20.100 g of magnesium hydroxide (Mg(OH).sub.2) (0.56 mol in terms of Mg), 21.540 g of zinc oxide (ZnO) (0.43 mol in terms of Zn), 77.282 g of germanium oxide (GeO.sub.2) (1.2 mol in terms of Ge), 0.088 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.920 g of europium oxide (Eu.sub.2O.sub.3) (0.008 mol in terms of Eu), and 0.064 g of thulium oxide (Tm.sub.2O.sub.3) (0.0005 mol in terms of Tm).

    [0092] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0093] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0094] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0095] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0096] X-ray diffraction analysis of the obtained red-luminescent phosphor of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+ is shown in FIG. 1. The host crystal phase was MgGeO.sub.3, indicating zinc ions occupied magnesium ions site in MgGeO.sub.3 crystal cell.

    [0097] A prior art phosphor with the formula of Mg.sub.0.4977Zn.sub.0.5GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+ was synthesized as a comparison.

    [0098] The excitation and emission spectra of the prior art phosphor and Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005 Tm.sup.3.sup.+ are shown in FIG. 2 and FIG. 3, respectively. For the prior art phosphor, besides the red emission peak of 680 nm, it also shows a sub-green emission peak of 530 nm. Therefore, the florescence performance of the prior art phosphor is a combination of red and green. For the phosphor obtained in Example 1 with the formula of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, the emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation for both was ranging in UV region with a peak of 230 nm.

    [0099] The tested afterglow duration of the prior art phosphor and Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, based on the testing standard of DIN 67510-1, is shown in FIG. 4. It should be noted here that according to the standard of DIN 67510-1, a 10001x D65 light source is adopted as excitation source, which is an artificial daylight 6500 K. Because it is a full-spectrum light source, UV light only accounts for a small part, the power absorbed by the phosphor is much less than pure UV light source. The tested afterglow duration for prior art phosphor and Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+ is 54 and 80 minutes, respectively (to the time that the afterglow luminance decreased to 0.32 mcd/m.sup.2).

    [0100] As a comparison, a 16 W 308 nm UV light source was also adopted to replace the D65 light source to excite the phosphor of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+. After irradiating onto the sample for 5 minutes, the resulted afterglow duration is 8 hours and 20 minutes, as shown in FIG. 5.

    Example 2

    [0101] Based on the formula of Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+, the following starting materials were weighted: 12.337 g of magnesium hydroxide (Mg(OH).sub.2) (0.39 mol in terms of Mg), 26.485 g of zinc oxide (ZnO) (0.60 mol in terms of Zn), 68.077 g of germanium oxide (GeO.sub.2) (1.2 mol in terms of Ge), 0.385 g of manganese oxide (MnO) (0.01 mol in terms of Mn), 0.286 g of europium oxide (Eu.sub.2O.sub.3) (0.003 mol in terms of Eu), and 0.052 g of thulium oxide (Tm.sub.2O.sub.3) (0.0005 mol in terms of Tm).

    [0102] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0103] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0104] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0105] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0106] The excitation and emission spectra of Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+, is shown in FIG. 6. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm. Comparing with excitation spectrum of prior art phosphor and the formula described in Example 1, the effective excitation region of UVB increases. In addition, the excitation region extends to visible light region.

    [0107] The tested afterglow duration of the prior art phosphor and Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+, based on the testing standard of DIN 67510-1, is shown in FIG. 7. The tested afterglow duration for prior art phosphor and Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+ was 54 and 57 minutes, respectively. More attractively, the initial afterglow intensity of Mg.sub.0.39Zn.sub.0.60Ge.sub.1.2O.sub.3: 0.01Mn.sup.2+, 0.003Eu.sup.3+, 0.0005Tm.sup.3.sup.+ is 12 times greater than that of the prior art phosphor.

    Example 3

    [0108] Based on the formula of Mg.sub.0.56Zn.sub.0.43GeO.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, the following starting materials were weighted: 20.100 g of magnesium hydroxide (Mg(OH).sub.2) (0.56 mol in terms of Mg), 21.540 g of zinc oxide (ZnO) (0.43 mol in terms of Zn), 64.402 g of germanium oxide (GeO.sub.2) (1.0 mol in terms of Ge), 0.088 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.920 g of europium oxide (Eu.sub.2O.sub.3) (0.008 mol in terms of Eu), and 0.064 g of thulium oxide (Tm.sub.2O.sub.3) (0.0005 mol in terms of Tm).

    [0109] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0110] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0111] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0112] The resulted product was made to powder, through a grinding step, to obtain the phosphor.

    [0113] The excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43GeO.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+is shown in FIG. 8. Two emission peaks can be observed with one centered at 680 nm and the other centered at 530 nm, demonstrating a red and green emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0114] The tested afterglow duration of Mg.sub.0.56Zn.sub.0.43GeO.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Tm.sup.3.sup.+, based on the testing standard of DIN 67510-1, is shown in FIG. 9. The tested afterglow duration was only 3 minutes. Without adding an excessive amount of germanium, although the afterglow is still peaked at 680 nm, the afterglow duration decreases significantly, while most of the photon energy consumes on 530 nm green florescent emission. Thus in the present invention, an excessive amount of germanium helps host to form a compact crystal lattice and avoid of 530 nm green florescent emission.

    Example 4

    [0115] Based on the formula of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Er.sup.3+, the following starting materials were weighted: 20.100 of magnesium hydroxide (Mg(OH).sub.2) (0.56 mol in terms of Mg), 21.580 g of zinc oxide (ZnO) (0.43 mol in terms of Zn), 77.282 g of germanium oxide (GeO.sub.2) (1.2 mol in terms of Ge), 0.088 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.920 g of europium oxide (Eu.sub.2O.sub.3) (0.008 mol in terms of Eu), and 0.064 g of erbium oxide (Er.sub.2O.sub.3) (0.0005 mol in terms of Er).

    [0116] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0117] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0118] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0119] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0120] The excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Er.sup.3+ is shown in FIG. 10. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0121] The tested afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Er.sup.3+, based on the testing standard of DIN 67510-1, is shown in FIG. 11. The tested afterglow duration was 50 minutes.

    Example 5

    [0122] Based on the formula of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Ho.sup.3+, the following starting materials were weighted: 20.100 of magnesium hydroxide (Mg(OH).sub.2) (0.56 mol in terms of Mg), 21.580 g of zinc oxide (ZnO) (0.43 mol in terms of Zn), 77.282 g of germanium oxide (GeO.sub.2) (1.2 mol in terms of Ge), 0.088 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.920 g of europium oxide (Eu.sub.2O.sub.3) (0.008 mol in terms of Eu), and 0.062 g of holmium oxide (Ho.sub.2O.sub.3) (0.0005 mol in terms of Ho).

    [0123] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0124] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0125] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0126] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0127] The excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Ho.sup.3+ is shown in FIG. 12. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0128] The tested afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Ho.sup.3+, based on the testing standard of DIN 67510-1, is shown in FIG. 13. The tested afterglow duration was 32 minutes.

    Example 6

    [0129] Based on the formula of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Pr.sup.3+, the following starting materials were weighted: 20.100 of magnesium hydroxide (Mg(OH).sub.2) (0.56 mol in terms of Mg), 21.580 g of zinc oxide (ZnO) (0.43 mol in terms of Zn), 77.282 g of germanium oxide (GeO.sub.2) (1.2 mol in terms of Ge), 0.088 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.920 g of europium oxide (Eu.sub.2O.sub.3) (0.008 mol in terms of Eu), and 0.056 g of praseodymium oxide (Pr.sub.6O.sub.11) (0.0005 mol in terms of Pr).

    [0130] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0131] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0132] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0133] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0134] The excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Pr.sup.3+ is shown in FIG. 14. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0135] The tested afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Pr.sup.3+, based on the testing standard of DIN 67510-1, is shown in FIG. 15. The tested afterglow duration was 31 minutes.

    Example 7

    [0136] Based on the formula of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Nd.sup.3+, the following starting materials were weighted: 20.100 of magnesium hydroxide (Mg(OH).sub.2) (0.56 mol in terms of Mg), 21.580 g of zinc oxide (ZnO) (0.43 mol in terms of Zn), 77.282 g of germanium oxide (GeO.sub.2) (1.2 mol in terms of Ge), 0.088 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.920 g of europium oxide (Eu.sub.2O.sub.3) (0.008 mol in terms of Eu), and 0.056 g of neodymium oxide (Nd.sub.2O.sub.3) (0.0005 mol in terms of Nd).

    [0137] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0138] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0139] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0140] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0141] The excitation and emission spectra of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Nd.sup.3+ is shown in FIG. 16. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0142] The tested afterglow duration of Mg.sub.0.56Zn.sub.0.43Ge.sub.1.2O.sub.3: 0.002Mn.sup.2+, 0.008Eu.sup.3+, 0.0005Nd.sup.3+, based on the testing standard of DIN 67510-1, is shown in FIG. 17. The tested afterglow duration was 53 minutes.

    Example 8

    [0143] Based on the formula of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.003Eu.sup.3+, 0.001Sm.sup.3+, the following starting materials were weighted: 17.288 g of magnesium hydroxide (Mg(OH).sub.2) (0.49 mol in terms of Mg), 24.616 g of zinc oxide (ZnO) (0.50 mol in terms of Zn), 63.274 g of germanium oxide (GeO.sub.2) (1.0 mol in terms of Ge), 0.086 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.319 g of europium oxide (Eu.sub.2O.sub.3) (0.003 mol in terms of Eu), and 0.106 g of samarium oxide (Sm.sub.2O.sub.3) (0.001 mol in terms of Sm).

    [0144] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0145] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0146] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5 degrees centigrade per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0147] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0148] The excitation and emission spectra of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.003Eu.sup.3+, 0.001Sm.sup.3+ is shown in FIG. 18. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0149] The tested afterglow duration of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.003Eu.sup.3+, 0.001Sm3.sup.+, based on the testing standard of DIN 67510-1, is shown in FIG. 19. The tested afterglow duration was 18 minutes.

    Example 9

    [0150] Based on the formula of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+, 0.0003Yb.sup.3+, the following starting materials were weighted: 16.125 g of magnesium hydroxide (Mg(OH).sub.2) (0.49 mol in terms of Mg), 22.605 g of zinc oxide (ZnO) (0.50 mol in terms of Zn), 69.725 g of germanium oxide (GeO.sub.2) (1.0 mol in terms of Ge), 0.079 g of manganese oxide (MnO) (0.002 mol in terms of Mn), 0.029 g of europium oxide (Eu.sub.2O.sub.3) (0.0003 mol in terms of Eu), and 0.033 g of ytterbium oxide (Yb.sub.2O.sub.3) (0.0003 mol in terms of Yb).

    [0151] The above starting materials were then put into a nylon ball milling jar with zirconia milling balls. The milling medium is ethanol. A planetary mill machine was adopted to sufficiently mix the starting materials for 2 hours.

    [0152] The resulting mixture was transferred into a clean tray and baked at 80° C. for overnight to fully evaporate ethanol. Then the dried mixture was sieved with a 120 mesh sieve.

    [0153] The sieved mixture was put into an aluminum oxide crucible with an aluminum oxide lid covered on. Place the above into a muffle furnace. Heat the furnace from room temperature to 1220° C. with a rate of 5° C. per minute. Keep sintering at 1220° C. for 5 hours and naturally cool down to room temperature. All of the heating, sintering and cooling process were conducted in air atmosphere.

    [0154] The resulted product was made to powder, through a grinding step, to obtain the red-luminescent long-afterglow phosphor.

    [0155] The Excitation and emission spectra of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+, 0.0003Yb.sup.3+ is shown in FIG. 20. The emission peak centered at 680 nm, demonstrating a pure red emission. The effective excitation was ranging in UV region with a peak of 230 nm.

    [0156] The tested afterglow duration of Mg.sub.0.49Zn.sub.0.50GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+, 0.0003Yb.sup.3+, based on the testing standard of DIN 67510-1, is shown in FIG. 21. The tested afterglow duration was 69 minutes.

    [0157] The comparisons of afterglow luminance of the synthesized samples mentioned above are shown in Table 1, wherein the relative afterglow luminance of each sample are shown by taking the afterglow luminance of Mg.sub.0.4977Zn.sub.0.5GeO.sub.3: 0.002Mn.sup.2+, 0.0003Eu.sup.3+ as prior art or 100.

    TABLE-US-00001 Afterglow (Relative luminance) tested based on the standard of DIN 67510-1 Example No. After 1 s After 60 s After 300 s After 600 s After 1200 s After 1800 s After 2400 s After 3000 s prior art 100 100 100 100 100 100 100 100 1-hostl 41 55 76 85 97 97 111 119 2-host2 1267 697 271 158 110 100 100 103 3-host3 28 25 0 0 0 0 0 0 4-Er 55 56 68 78 87 86 87 0 5-Ho 48 56 99 64 62 59 0 0 6-Pr 38 46 53 56 58 57 0 0 7-Nd 50 63 84 97 101 102 98 94 8-Sm 16 16 22 31 0 0 0 0 9-Yb 95 93 81 69 66 72 82 100

    [0158] As described above, by appropriately designing the host formulation as well as activator, first sensitizer and second sensitizer, the red-luminescent long-afterglow phosphor of the present invention performs excellent luminescence performance including long afterglow duration and an emission peak of 680 nm, indicating red luminescence. The synthesis process is easy and environmental friendly. The resulted phosphor is chemically stable. The powder color of the present phosphor at non-excited state is white and can be applied into polymer matrix to prepare luminescent inks, paints, plastics, etc without deviation of polymer matrix color itself.

    [0159] Thus, it can be seen that an improved red-luminescent phosphor with long afterglow has been disclosed which eliminates or at least diminishes the disadvantages and problems associated with prior art products and processes.

    [0160] Although the invention has been described in terms of certain embodiments, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims which follow.