Conical structures with hollow interiors, namely, nanocones (NCs), may exhibit better carrier transport properties than nanorods or nanotubes, which make them promising candidates for potential applications in optical/display devices, electronics and optoelectronics. Generally, conical structures belong to a metastable state between lamellar and tubular forms due to the extreme curvature causing the increase of internal strain energy. Therefore, it is very difficult to prepare NCs in high yield and purity under mild conditions. Here we firstly demonstrate a general strategy for the synthesis of layered rare-earth hydroxide (LRH) NCs intercalating dodecyl sulfate anions (CHSO, DS) using hexamethylenetetramine (CHN, HMT) hydrolysis. The rare-earth cations (RE) in the host layer can be conveniently modified and/or doped, resulting in a large family of monometallic (Y, Tb, Er), bi- (Y-Tb, Y-Er) and even tri-metallic (Y-Yb-Er) LRH NCs with adjustable ratios. Moreover, the DS-intercalated LRH NCs can be readily modified with various inorganic or organic anions (e.g., NO, Cl, and CHCOO, etc.) through a conventional anion-exchange procedure, and the original conical morphology can be perfectly maintained. The anion-exchanged product, for example, NO-intercalated NCs, can be more easily and topotactically transformed into oxide NCs than the original DS-intercalated form, exempt from the formation of rare-earth oxysulfates induced by the combustion of interlayer DS anions. Taking advantage of this protocol, tri-metallic (Y-Yb-Er) LRH NCs were anion-exchanged into the NO-intercalated form and subsequently calcined into YO:Yb,Er oxide NCs, which showed efficient upconversion photoluminescence properties. The current strategy may become a general method for the designed synthesis of other related hydroxide and oxide NCs for a wide range of potential applications.

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positively charged octahedral hydroxide host layers and hydrated anions intercalated in the interlayer gallery. [9][10][11][12] The well-known LDHs, with a general formula of M 2+1-x M 3+ x (OH) 2 A n− x/n ·mH 2 O (M 2+ and M 3+ , the bivalent and trivalent metal cations, respectively; A n− , the nonframework charge-balancing anions), are a class of hydrotalcite-like hydroxides, e.g., Mg 6 Al 2 (OH) 16 (CO 3 )·4H 2 O, namely anionic clay found in nature, important in geochemistry, mineralogy, and materials science. [13,14] In recent years, the M 2+ −Al 3+ LDHs have been widely pursued due to the facts that it is very difficult to fabricate non-Al 3+ LDHs via a homogeneous precipitation. [15][16][17] Very recently, we have developed an innovative method to prepare all-transition-metal LDHs through the topological transformation of the corresponding transition-metal brucite hydroxides (M 2+ (OH) 2 ) by halogen oxidation in organic solvent. [18] LMHs, with the common formula of M 2+ (OH) 2-x A n− x/n ·mH 2 O, have an analogous structure as LDHs and consist of positively charged brucite-like host layers with charge-balancing anions in the gallery, which have recently attracted tremendous attention as electrode materials in supercapacitors and catalysts in water splitting. [19][20][21][22] Partly due to their tunable parameters such as the diversity of cations (M 2+ and/or M 3+ ) in hydroxide host layers, inorganic/organic anion (A n− ) in the interlayer gallery, layered hydroxides involve a large family of isostructural materials with outstanding intercalation and anion-exchange capability.In particular, layered rare-earth hydroxides (LRHs), with a general chemical formula of RE(OH) 2.5 (A n− ) 0.5/n ·nH 2 O (RE: trivalent rare-earth cations; A n− : interlayer n-valent anions), as a new and important class of functional layered hydroxides, have attracted extensive interest duo to their unique luminescence and electronic properties as well as significant applications in various fields, such as high performance luminescence, upconversion materials, downconversion materials, and so forth. [23][24][25] LRHs have been successfully synthesized in recent years through homogeneous precipitation method by using soluble rare-earth salts as the RE source and hexamethylenetetramine (C 6 H 12 N 4 , HMT) as a hydrolysis agent. [26] However, most of It is demonstrated herein that a series of terbium ions (Tb3+ )-doped layered yttrium hydroxide (LYH:Tb) nanocones (NCs) intercalating dodecyl sulfate (C 12 H 25 SO 4 , DS) anions can be successfully synthesized in large quantities through a facile hydrothermal strategy. The DS anions in the interlayer gallery of LYH:Tb NCs can be readily modified with various anions (such as NO 3 − , Cl − , and CH 3 COO − ) through a convenient anion-exchange procedure. The luminescent properties of LYH:Tb NCs are sensitively influenced by the dopant concentration and the interlayer anions. In particular, the original DS − -intercalated form and the anion-exchanged product can be topotactically convert...