A quantum dot includes: a core including at least one first positive ion precursor and at least one negative ion precursor; a shell including at least one second positive ion precursor and at least one negative ion precursor and wrapping the core; and a ligand formed on a surface of the shell, wherein the first positive ion precursor is an n-period element and the second positive ion precursor is an (n-1)-period element, where n is an integer of 3 to 6.

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 colored contact lens includes an iris region made of a first mixed liquid, and the first mixed liquid includes a colored material and a contact lens material. The colored material absorbs and stores light when in a well lit environment and emits lights when in a poorly lit environment or a dark environment. Therefore, when the colored contact lens is located in a well lit environment, light is absorbed and stored, and when the contact lens is in a poorly lit environment or the dark environment light is emitted.

The present disclosure provides a precursor composition and a method for preparing inorganic nanocrystals. The precursor composition is used to prepare inorganic nanocrystals and is in the form of a gel, the precursor composition includes a precursor and an organogel medium for dispersing the precursor, and the precursor is one or more of a cationic precursor, an anionic precursor. The precursor composition not only greatly expands the selection range of potential precursors and their concentration range, but also simplifies the synthesis system of the nanocrystals and minimizes the impact on the environment, and improves the stability or repeatability of the method of preparing the inorganic nanocrystals.

A near-infrared fluorescent quantum dot for achieving rapid renal clearance, and a preparation method and application thereof are provided. The preparation method includes the following steps: carrying out a solvothermal reaction on a first uniformly mixed reaction system including a first probe of a near-infrared fluorescent quantum dot and a weakly polar solvent to prepare a second probe of the near-infrared fluorescent quantum dot with a particle size of less than 5 nm; and then mixing the second probe of near-infrared fluorescent quantum dot with a hydrophilic ligand to form a second uniformly mixed reaction system for a ligand exchange reaction, thus obtaining a near-infrared fluorescent quantum dot for achieving rapid renal clearance, which has a fluorescence emission wavelength ranging from 700 nm to 1700 nm. The near-infrared fluorescent quantum dot for achieving renal clearance is obtained through a simple solvothermal reaction and a subsequent ligand exchange method.

The present application discloses a method for preparing metal oxide nanoparticles, including the following steps: providing an organic reagent with a molecular formula of X(SO.sub.2)Y and a metal oxide nanoparticle sample, in which the metal oxide nanoparticle sample is an aqueous metal oxide nanoparticle; in X(SO.sub.2)Y, X contains polar functional groups; mixing the organic reagent and the metal oxide nanoparticle sample in a liquid medium and adding an alkaline reagent to a mixed solution of the organic reagent and the metal oxide nanoparticle sample to prepare the metal oxide nanoparticles. The method provided in the present application can reduce the surface defect state of metal oxide nanoparticles, thereby improving the stability of metal oxide nanoparticles.