Room-temperature lasing from fluorene thin-film crystals densely doped with anthracene.
The potential for room-temperature lasing in densely doped organic crystals has been examined using (fluorene)0.8-(anthracene)0.2 thin crystals fabricated in a narrow gap between two quartz plates. An excitation-intensity dependence study confirms that the system shows spectral line narrowing, a super linear increase of the narrow line above threshold excitation intensity, and laser cavity modes. These results indicate that lasing has been observed in the densely doped organic crystal, which contains in-plane cavities with a length of approximately 100 μm.
Lasing in organic mixed-crystal thin films with cavities composed of naturally formed cracks.
This study investigates the possibility that a crack pair that is naturally formed in the course of sample preparation functions as a laser cavity. Lasing with longitudinal mode structures has been reported in mixed-crystal thin films composed of fluorene and anthracene without artificial cavity structure. In the present study, it was shown that lasing is observed only when an excitation spot covers parallel pairs of cracks. The longitudinal mode intervals of the stimulated emission spectra for several crack pairs were found to be proportional to the inverse of the crack spacing. Furthermore, the interval for the artificially fabricated metal cavity followed the same linear relation. These results indicate that the crack pairs can function as laser cavities.
Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.