Er³⁺‐Doped Anatase TiO₂ Nanocrystals: Crystal‐Field Levels, Excited‐State Dynamics, Upconversion, and Defect Luminescence

Abstract

A comprehensive survey of electronic structure and optical properties of rare-earth ions embedded in semiconductor nanocrystals (NCs) is of vital importance for their potential applications in areas as diverse as luminescent bioprobes, lighting, and displays. Er3+ -doped anatase TiO2 NCs, synthesized via a facile sol-gel solvothermal method, exhibit intense and well-resolved intra-4f emissions of Er3+ . Crystal-field (CF) spectra of Er3+ in TiO2 NCs are systematically studied by means of high-resolution emission and excitation spectra at 10-300 K. The CF analysis of Er3+ assuming a site symmetry of C(2v) yields a small root-mean-square deviation of 25.1 cm(-1) and reveals the relatively large CF strength (549 cm(-1) ) of Er3+, thus verifying the rationality of the C(2v) symmetry assignment of Er3+ in anatase TiO2 NCs. Based on a simplified thermalization model for the temperature-dependent photoluminescence (PL) dynamics from (4) S(3/2) , the intrinsic radiative luminescence lifetimes of (4) S(3/2) and (2) H(11/2) are experimentally determined to be 3.70 and 1.73 μs, respectively. Green and red upconversion (UC) luminescence of Er3+ can be achieved upon laser excitation at 974.5 nm. The UC intensity of Er3+ in Yb/Er-codoped NCs is found to be about five times higher than that of Er-singly-doped counterparts as a result of efficient Yb3+ sensitization and energy transfer upconversion (ETU) evidenced by its distinct UC luminescence dynamics. Furthermore, the origin of defect luminescence is revealed based on the temperature-dependent PL spectra upon excitation above the TiO2 bandgap at 325 nm.

Ultimately simple one-pot single-step synthesis of rare earth doped spherical mesoporous metal oxide nanospheres with upconversion emission ability in supercritical methanol

“…S10b). Similar to the prototype 12 CeO 2 :Er NPs, two emission bands were observed at around 550 and 680 nm in the photoluminescence spectra of the NPs (Fig. 4d and e).…”

“…Consequently, these NPs have attracted much attention for their potential applications in optical communications, optoelectronic devices, flat panel displays, photodynamic therapy, and biosensors [3][4][5][6][7][8][9][10]. Several RE dopants, such as Er 3+ [11][12][13][14][15][16], Eu 3+ [17][18][19], Sm 3+ [20,21], Tm 3+ [22], and Ho 3+ [23], have been utilized as luminescent centers. To reduce multiphonon relaxation and concentration quenching, the host materials of the UCNPs fixing the dopant in the appropriate position should be carefully selected.…”

“…Metal oxides are one of the best host materials for RE ions because many of them, such as CeO 2 , ZrO 2 , TiO 2 , etc. are highly transparent to visible light and possess strong mechanical, optical, and thermal stabilities and properties [11][12][13][14][15][16][17][18][19][20][21][22]. and high-resolution transmission electron microscopy images were taken using JEOL JEM-2100F.…”

Synthetic versatility of nanoparticles: A new, rapid, one-pot, single-step synthetic approach to spherical mesoporous (metal) oxide nanoparticles using supercritical alcohols

“…These results confirmed that Yb co-doped CeO 2 :Er MARIMO NPs with efficient UC emission were successfully prepared via the one-pot, single-step reaction in scMeOH. To the best of our knowledge, previously reported NPs always required calcination to achieve emission [82][83][84][85][86][87]. However, in the present case, calcination is not necessary for UC emission, even under low power IR laser irradiation (980 nm, 10 mW), which could be because of the unique light harvesting properties of the mesoporous structure of the MARIMO NPs [46,88].…”

Lanthanide-doped semiconductor nanocrystals: electronic structures and optical properties

“…[174] [178]. According to the high-resolution PL excitation and emission spectra at 10 K, 45 CF levels belonging to 12 different SLJ multiplets of 4f 11 configuration of Er 3+ were experimentally determined (Table 4) and subjected to energy level fitting [180]. The energy-level-fitting was performed using the f-shell empirical programs of Prof. Reid, which enabled a complete diagonalization without truncation of the 4f 11 wave functions [185].…”