Theoretical and Experimental Study on Exciton Properties of TT-, T-, and H-Nb₂O₅

Abstract

We have theoretically and experimentally studied exciton properties of three normal Nb 2 O 5 polymorphs, including pseudo-hexagonal (TT-), orthorhombic (T-), and monoclinic (H-) phases. Theoretical work shows that the exciton binding energy for H-Nb 2 O 5 is 73.553 meV, much higher than that for TT-Nb 2 O 5 (3.515 meV) and T-Nb 2 O 5 (24.071 meV). The H-Nb 2 O 5 material, as characterized by field-induced surface photovoltage spectroscopy, uniquely presents bound exciton states near the bottom of the conduction band. Thermogravimetric analysis and photoluminescence (PL) lifetime demonstrate that the bound exciton states in H-Nb 2 O 5 originate from interactions between the exciton pairs and oxygen vacancy sites. Such excitons in H-Nb 2 O 5 can be effectively dissociated into free electrons and holes with the incorporation of the oxygen vacancies, leading to the longer PL lifetime. This work allows one to find correlations between material structures and exciton properties, which will provide some basic knowledge to optimize materials for optoelectronic and photonic performance.

Novel Nonstoichiometric Niobium Oxide Anode Material with Rich Oxygen Vacancies for Advanced Lithium-Ion Capacitors

“…Recently, niobium-based oxides, such as TT-Nb 2 O 5 , T-Nb 2 O 5 , and H-Nb 2 O 5 , have raised considerable attention due to the relatively high capacity (200–300 mAh g –1 ), fast Li + ion diffusion kinetics, and safe operating voltage (1.0–3.0 V vs Li/Li + ), which are expected to offer a way out of this dilemma of LICs. − For example, H-Nb 2 O 5 can offer a practical capacity of as high as over 250 mAh g –1 and high diffusion coefficient ( D Li+ = 10 –10 –10 –12 cm 2 s –1 ) . Nevertheless, the performance of niobium-based oxide electrodes is still restricted by the inherent low electrical conductivity (10 –11 –10 –6 S cm –1 ) .…”

In-Depth Investigation of the Mechanism of Dehydration-Induced Phase Transformation from Nb3O7(OH) to H-Nb2O5: A Theoretical and Experimental Approach

“…The SPV onset for Nb 2 O 5 •nH 2 O-H is at around 450 nm, which is consistent with our previous report. 6 The Nb-H and Nb 3 O 7 (OH)-H samples have onsets at about 420 and 400 nm, respectively. The lower photovoltage intensity and narrower response range for Nb 3 O 7 (OH)-H indicate the lowest separation efficiency of the photogenerated electron− hole pairs.…”

“…Obviously, the Nb 3 O 7 (OH)-H showed a remarkably different photovoltage behavior, compared to that of Nb-H and Nb 2 O 5 •nH 2 O-H. For the Nb 2 O 5 •nH 2 O-H, and Nb-H samples, two pronounced SPV response bands were observed in the range 300−500 nm, in agreement with the previous results of our group. 6 The bands P 1 at 300−400 nm and P 2 at 400−500 nm are assigned to band-to-band transition and exciton transition, respectively. 6 The surface voltage response of band P 2 can be attributed to the interaction between the free exciton pairs and donor states to form bound exciton states, and the donor state levels with strong electron trapping ability are mainly associated with oxygen vacancies.…”

Morphological Control: Properties and Applications of Metal Nanostructures

“…ese plasmatic interactions can be controlled by changing the morphology and dimensions of metal nanostructures [8][9][10]. Applications related to the field of nanoplasmatic include super lenses, Raman-enhanced surface spectroscopy (SERS), molecular spectroscopy, plasmonic-enhanced fluorescence, quantum computing, energy-dependent photochemical lithography, energy-assisted plasma ionization [11][12][13][14][15]. Silver is more than 50 times cheaper than gold, and because of its unique physicochemical properties, it is a good choice for use in plasmatic applications [16][17][18].…”