Absolute external luminescence quantum efficiency of zinc oxide

Abstract

We report on the measurement of the absolute external luminescence quantum efficiency of various ZnO samples using a miniature integrating sphere fitted into a cryostat. Even the absolute luminescence quantum efficiencies per spectral interval are directly accessible. Measurements have been carried out on high quality bulk samples and different commercially available ZnO powders from 8K up to room temperature. Activated processes lead to an overall decrease in the efficiency with temperature. All efficiencies are considerably below unity, making the identification of the luminescence decay time with the radiative life time very questionable.

High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires

“…In contrast to the low EQE values typically reported for bulk semiconductor materials [5][6][7] , we found that the EQE of single-crystal ZnO nanowires can be higher than 20%. The high material quality was also indicated by an internal quantum efficiency (IQE) of 62%.…”

“…This EQE value is significantly higher than reported values of ZnO powders (1 -3%) using similar excitation and measurement schemes. 6,11 Not only is the measured EQE of ZnO nanowires larger than that measured from high-purity ZnO powder ( Figure S4, Supporting Information), it originates from bottom-up synthesized semiconductor nanostructures that offer functional geometries for device applications. Such high EQE values were achieved by optimization of nanowire growth with reaction temperature and oxygen pressure to produce nanowires with minimal point defects that are deleterious to band-edge emission.…”

Photoluminescence studies on MBE grown Co-doped ZnO thin films fabricated through ion implantation and swift heavy ion irradiation

“…The most probable values obtained for E 0 1 , E 1 and E 2 are listed in Table 1 along with the nature of thermal quenching and the respective peak energy values. It can be seen from the table that, the activation energies 41-49 meV obtained for the E 0 1 of I 3 peak at 3.365 eV of both un-doped and Co-doped ZnO films are in agreement with the value 42 meV (peak D at 3.3606 eV) of Watanabe et al [16] and the 33 meV (peak in the spectral range 3.00-3.46 eV) of Hauser et al [18]. However, with the Co doping the NTQ characteristics showed a considerable change, as can be seen in the nature of the curve and the estimated activation energies.…”

“…Recently, Shibata [15] suggested the principal mechanism of NTQ as a thermal excitation of electrons into the initial state of the PL transition from the eigen-states with smaller energy eigen-values. The NTQ was also observed in single crystals, nanorods and bulk samples of un-doped ZnO and in Ga-doped ZnO thin films [16][17][18]. Meyer et al [19] explained the NTQ behavior of I 6B /I 8B donor bound exciton PL peaks at 15-20 K in ZnO crystal, through fitting an analytical equation, in terms of the emergence of excited states involving B-valence band.…”

Visible emission characteristics from different defects of ZnS nanocrystals

“…6a). That is, the intensity of the green emission band shows a clear increase with increasing temperature in the temperature range from 150 K to 200 K. This phenomenon has been widely studied in ZnO nanocrystals in recent years, 49,50 and is referred to as negative thermal quenching (NTQ).…”