Graphene quantum dots are known to exhibit tunable photoluminescence (PL) through manipulation of edge functionality under various synthesis conditions. Here, we report observation of excitation dependent anomalous m-n type fingerprint PL transition in synthesized amino functionalized graphene quantum dots (5-7 nm). The effect of band-to-band π*-π and interstate to band n-π induced transitions led to effective multicolor emission under changeable excitation wavelength in the functionalized system. A reasonable assertion that equi-coupling of π*-π and n-π transitions activated the heterogeneous dual mode cyan emission was made upon observation of the PL spectra. Furthermore, investigation of incremented dimensional scaling through facile synthesis of amino functionalized quantum graphene flakes (20-30 nm) revealed it had negligible effect on the modulated PL pattern. Moreover, an effort was made to trace the origin of excitation dependent tunable heterogeneous photoluminescence through the framework of energy band diagram hypothesis and first principles analysis. Ab initio results suggested formation of an interband state as a manifestation of p orbital hybridization between C-N atoms at the edge sites. Therefore comprehensive theoretical and experimental analysis revealed that newly created energy levels can exist as an interband within the energy gap in functionalized graphene quantum structures yielding excitation dependent tunable PL for optoelectronic applications.

Highly-luminescent nanophosphors have a decisive role in solid-state lighting (SSL) as well as in field emission display (FED) applications due to their potential use in fabrication of nanophosphor based FED and solid state display devices. Herein, the red emitting highly-luminescent Eu(3+)-Li(+) co-doped magnesium aluminate (MgAl2O4) nanophosphors were synthesized by a customized sol-gel route with an average particle size of 18 nm, which can be easily scaled up in a large quantity. The resulting nanophosphor exhibits hypersensitive red emission, peaking at 615 nm upon 394 nm excitation. Furthermore, comparative photoluminescence (PL) studies have been carried out for Eu(3+) doped and Eu(3+) doped-Li(+) co-doped magnesium aluminate (Li(+) co-doped MgAl2O4:Eu(3+)) nanophosphors, which indicated that Li(+) co-doping significantly improves luminescence intensity along with good crystallinity. Moreover, the charge compensation by addition of Li(+) co-activator in MgAl2O4:Eu(3+) lattice led to the two fold enhancement of PL intensity. The obtained results suggest that this nanophosphor could be an ultimate choice for next generation advanced luminescent nanomaterials for solid state lighting and portable FED devices.

Solid-state lighting (SSL) and field emission based display (FED) devices collectively encompass a major fraction of contemporary research efforts and thus development of a newer generation of highly luminescent nanophosphors presently defines a critical juncture for further development of this still somewhat-nascent field. However, the low efficiency of red phosphors constitutes a principal bottleneck for commercialization of such devices. Herein, we present a red light emitting highly luminescent Na + codoped CaSnO 3 :Eu 3+ nanophosphor with an average particle size of 32 nm that has been synthesized by a modified sol−gel technique. The resultant nanophosphor exhibits bright red emission under both UV and low voltage electron beam excitations. Furthermore, quantitative assessments of photoluminescence (PL) signatures for Eu 3+ doped and Na + codoped CaSnO 3 :Eu 3+ nanophosphors conclusively demonstrate that Na + codoping facilitates an almost 4-fold increase in the luminescence intensity coupled with significant improvement in thermal stability. In addition, charge compensation by incorporation of Na + leads to an increased order of radiative transition and thereby increases the color purity and lifetime of radiative transition. Obtained results firmly and unambiguously establish the bright and revolutionary prospects of this new type of nanophosphor in the rapidly emerging field of solid state lighting and FED devices.

In the current report, chemically synthesized copper phthalocyanine (CuPc) nanotubes are shown to exhibit unprecedentedly well cold cathode emission characteristics with turn-on field (3.2 V μ m(-1)) and stable emission during long intervals (200 min). Simulation of electric field distribution via finite element method around an isolated nanotube emitter in a manner parallel to the experimental setup (inter-electrode distance = 180 μm) exhibits good corroboration of theoretical premises with experimental findings. Obtained results strongly indicate CuPc nanotubes to be potential candidate as cold cathode emitter for electron emission based applications such as field emission displays and vacuum nano-electronic devices.

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