Multiphoton excited luminescence is of paramount importance in the field of optical detection and biological photonics. Self-trapped exciton (STE) emission with self-absorption-free advantages provide a choice for multiphoton excited luminescence. Herein, multiphoton excited singlet/triplet mixed STE emission with a large full width at half-maximum (617 meV) and Stokes shift (1.29 eV) has been demonstrated in single-crystalline ZnO nanocrystals. Temperature dependent steady state, transient state and time-resolved electron spin resonance spectra demonstrate a mixture of singlet (63%) and triplet (37%) mixed STE emission, which contributes to a high photoluminescence quantum yield (60.5%). First-principles calculations suggest 48.34 meV energy per exciton stored by phonons in the distorted lattice of excited states, and 58 meV singlet-triplet splitting energy for the nanocrystals being consistent with the experimental measurements. The model clarifies long and controversial debates on ZnO emission in visible region, and the multiphoton excited singlet/triplet mixed STE emission is also observed.
AlN based surface acoustic wave (SAW) filters with an acoustic wavelength (λ) of 8 µm have been fabricated based on sputtered AlN films on sapphire. The acoustic velocity of 1-µm-AlN/Sapphire bilayer structure is 5536 m/s, 60% higher than that of LiNbO. The central frequency, insertion loss, out-of-band rejection, and bandwidth of fabricated AlN based two-port type SAW filters with a delay gap of λ are 692 MHz, 25.58 dB, 35.40 dB, and 2.7 MHz, respectively. The impact of delay gap on the performance of AlN based filters have been studied experimentally. By the analysis of frequency response of SAW filters with delay gaps of λ, 15λ, and 30λ with and without time gating technique, we find that increase the delay gap of AlN based SAW resonators can improve the out-of-band rejection effectively because of the reduction of electromagnetic coupling, with a cost of a little degradation of insertion loss due to the small propagation loss of AlN/Sapphire bilayer. When the delay gap is increased from λ to 15λ, out-of-band rejection of AlN based filters is increased by 4.75 dB, while the insertion loss is only increased by 0.81 dB. When the delay gap is further increased from 15λ to 30λ, the suppression of out-of-band rejection is not obvious.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.