Correlation between structural and luminescent properties of Eu3+-doped ZnO epitaxial layers

Abstract

We have studied the epitaxial growth and photoluminescent (PL) properties of Eu3+-doped ZnO layers in correlation with structural analyses. Incorporation of Eu3+ ions into a ZnO host resulted in deterioration in crystal quality and lattice distortion. The spectral structure of Eu3+ emission revealed that Eu3+ ions were located at site symmetries lower than the original C3v of the Zn2+ ion sites in a hexagonal wurtzite structure of ZnO, which allowed for efficient red luminescence based on the electric dipole transitions. Moreover, we have found an anticorrelation of PL intensity between the excitonic and Eu3+ emissions, related to energy transfer from the ZnO host to the Eu3+ ions. The excitonic structure at the band edge was obscured upon doping with Eu3+ ions due to the formation of a band tail around 3.2 eV. This correlated with a reduction in excitonic emissions, leading to enhancement of Eu3+ emission. Strong PL emission from Eu3+ ions was only observed at low temperatures, and was remarkably suppressed with increasing temperature due to two types of nonradiative energy transfer paths. For the energy transfer process to Eu3+ ions, we suggest that the recombination energy of an electron–hole pair at the band tail near the band edge is close to that of high-lying excited levels in the Eu3+ 4f shell, providing an efficient energy pathway for the excitation of Eu3+ ions in the ZnO system.

Comparative first principles study of ZnO doped with group III elements

“…The same result has been found experimentally by A. Escobedo-Morals [33] as reported in table 1. The similar tendency are found by theoretical and experimental studies in the case of substitution Zn atoms by another atoms having a large ions radius, such Eu 3+ ( 0.97 Å) [34]and Cd 2+ (0.95 Å) [35]. Indeed, L.N.…”

Effects of mineralizing agent on the morphologies and photoluminescence properties of Eu3+-doped ZnO nanomaterials

“…Up to now, various techniques have been developed for controlling shape, size and structures of such nanomaterials [12][13][14][15][16][17][18][19]. Moreover, the spontaneous emission probability of rare-earth doping nanoparticles can be significantly modified by changing the particle size, shape and surrounding medium [20][21][22][23][24][25]. However, the investigation about the Eu-doped ZnO nanomaterials with different morphology, in particular, the effects of various mineralizing agents on their morphologies and photoluminescence properties are limited [26,27].…”

Structural characterization of impurified zinc oxide thin films

“…The solubility limit of Eu 3+ in ZnO is reported [12] to be approximately 1%. Regarding the deviation of lattice constants when introducing a RE, there are reports [28,29,30] on both a and c increase as compared with the undoped ZnO, while Badalawa et al [6] presented an opposite modification of lattice constants in Eu:ZnO thin films: a -constant increases with Eu concentration while cconstant has an inverse proportional dependence. Photoluminescence measurements are primarily employed to determine the oxidation state of europium ions due to different emission properties: blue (Eu 2+ ) or red (Eu 3+ ) phosphors [31,22].…”

“…For LED applications, ZnO host enables full color (from blue to red) via energy transfer to longer wavelength emitters [20]; in particular, trivalent europium doped ZnO (ZnO:Eu 3+ ) is suitable for optoelectronic applications involving red emission (the 5 D 0 → 7 F J (J = 0, 1, 2) transitions) while ZnO:Eu 2+ can be used for blue emission ( 4 f 5 6 d 1 (T 2g ) → 4 f 7 ( 8 S 7/2 ) transition) [20,12,21,22]. Europium doped ZnO nanostructures are nowadays investigated aiming different applications [23,24,25,26,27,6]. The solubility limit of Eu 3+ in ZnO is reported [12] to be approximately 1%.…”

“…There are numerous studies concerning the doping effect (nature and concentration) of the rare earths (RE) on the crystalline structure of certain materials [3,4,5], including ZnO [6,7,8]; using RE as dopants has an important drawback due to its limited solubility in various hosts [9,10,11,12]. Europium based compounds are of great interest due to its potential applications in spintronics [13,14,15,16,17] or for light emitting diodes (LEDs) [18,19].…”