Enhancement of the ultraviolet photoluminescence of ZnO films: Coatings, annealing, and environmental exposure studies

Abstract

To realize the many potential applications of ZnO films, it is vital to produce films with high optical quality that exhibit strong UV luminescence. By combining annealing at an optimal temperature followed by the deposition of a coating, one can achieve a significant enhancement of photoluminescence (PL). The effectiveness of the coating over time is a crucial point to be considered. Three types of coating materials were investigated: MgO, SiO2, and Al2O3. Due to its strong bond energy, MgO was found to be the most effective coating material for passivation of the surfaces of the ZnO films; SiO2 was the second best. The UV-PL intensity of MgO coated ZnO was found to increase by a factor of 52 relative to an uncoated film. The effectiveness of the coatings exhibited a linear correlation with their bond energies and is discussed in terms of competing mechanisms to surface passivation such as the adsorption of OH-groups; these can act as surface traps and diminish the UV-PL intensity. Annealing at 900 °C prior to the deposition of the coating was found to be an important step in realizing the optimal performance of the coating due to the reduction of Zn interstitials accompanied by improved crystallinity. Exposure to the environment, up to 294 days, results in the degradation of the UV-PL of the MgO coated film; this effect was not observed for the film coated with SiO2. This effect is discussed in terms of the strong reactivity of MgO with environmental contaminants from the OH-groups.

Optical properties of composite structure based on ZnO microneedles and Alq3 thin film

“…On the other side, the observed enhancement of luminescence intensity of both components under Alq 3 deposition can be caused by mutual in uence of each other. It has been found that passivation of ZnO lms by coatings with metal oxides [45] and doping with hydrogen [46] result in the strong UV ZnO luminescence enhancement. Alq 3 contains oxygen atoms and a lot of hydrogen atoms to promote this process.…”

Effects of thermal treatment on the complex structure of luminescence emission of Li-doped ZnO screen-printed films

“…As such substitution is possible for luminescent applications, the search for RE-free luminescent materials becomes a significant task. For a long time, ZnO-based materials have attracted considerable attention for possible applications in optoelectronic devices, particularly in the ultraviolet (UV) light emitters [9][10][11][12]. Visible-light-emitting materials with various spectral properties could also be obtained on the basis of ZnO because both blue luminescence and green luminescence have already been reported in the modified ZnO structures [13][14][15][16][17].…”

The role of CNT in surface defect passivation and UV emission intensification of ZnO nanoparticles

“…[12][13][14][15] Therefore, strategies to enhance the NBE consist of supressing defect formation during synthesis or post-growth. 16,17 Several, methods have been investigated to that end, which include surface state modification of ZnO by TiO 2 and Al 2 O 3 capping layers; hydrogenation [18][19][20] ; annealing under N 2 and O 2 [21][22][23] ; controlling defects during synthesis itself 24,25 ; and conjoining them with metal nanoparticles displaying surface plasmon resonance. 26,27 Organic and inorganic materials have witnessed enhancements in physical, chemical and structural properties when combined with CNT.…”