Photoluminescence and High-Temperature Persistent Photoconductivity Experiments in SnO₂ Nanobelts

Abstract

The Persistent Photoconductivity (PPC) effect was studied in individual tin oxide (SnO 2 ) nanobelts as a function of temperature, in air, helium, and vacuum atmospheres, and low temperature Photoluminescence measurements were carried out to study the optical transitions and to determine of the acceptor/donors levels and their best representation inside the band gap. Under ultraviolet (UV) illumination and at temperatures in the range of 200 to 400K we observed a fast and strong enhancement of the photoconductivity, and the maximum value of the photocurrent induced increases as the temperature or the oxygen concentration decreases. By turning off the UV illumination the induced photocurrent decays with lifetimes up to several hours. The photoconductivity and the PPC results were explained by adsorption and desorption of molecular oxygen at the surface of the SnO 2 nanobelts. Based on the temperature dependence of the PPC decay an activation energy of 230 meV was found, which corresponds to the energy necessary for thermal ionization of free holes from acceptor levels to the valence band, in agreement with the photoluminescence results presented. The molecular-oxygen recombination with holes is the origin of the PPC effect in metal oxide semiconductors, so that, the PPC effect is not related to the oxygen vacancies, as commonly presented in the literature.

On the electrical properties of distinct Eu3+ emission centers in the heterojunction GaAs/SnO2

“…The phenomenon of persistent photoconductivity (PPC) [21] has been found in rare-earth doped SnO 2 [22]. More recently, PPC has been found in SnO 2 nanobelts [23] and quantum dots [24]. Modeling the decay of PPC,…”

Luminescence studies on SnO2 and SnO2:Eu nanocrystals grown by laser assisted flow deposition

“…[14][15][16]22,[31][32][33][34][35][36][37][38][39][40] However, the peak position of the reported PL bands depends on the growth method and/or growth parameters used. [14][15][16]22,[31][32][33][34][35][36][37][38][39][40] However, the peak position of the reported PL bands depends on the growth method and/or growth parameters used.…”

Excitation dependent recombination studies on SnO2/TiO2electrospun nanofibers

“…The peak at ܲ ଵ ௌ violet emission might be due to near band edge emission 31 . Viana et.al 13 assigned the similar peak of ܲ ଵ ௌ to recombination of electrons from the CB to excitons bound to neutral (D 0 x). Kim et.al., 67 observed the peak at 416 nm (2.98 eV), but in the present studies a broad peak at ܲ ଶ ௌ is identified.…”

“…Since the energy of the emission band is lower than the band gap energy of SnO 2 (E g = 3.6 eV) 13,68 , the emission is not due to the direct recombination of a conduction electron in the 4p band of Sn and a hole in 2p VB of O 69 . The peak at ܲ ସ ௌ is assigned to isolated V O + centers, which lies at higher energy than the complex V O + center Ref 13 . In R 2 (see Fig 6d), a broad orange emission peaks identified as ܲ ହ ௌ and ܲ ௌ positioned at 562 and 585 nm.…”