Realization of sharp visible WGM lasing from Sm³⁺ :ZnO micro-spheres fabricated by laser ablation technique

Abstract

In this paper, the whispering gallery mode lasing from Sm 3+ doped ZnO micro-spheres operating in the visible wavelength range 550-750 nm is studied. Highly smooth and crystalline Sm 3+ :ZnO micro-spheres of various diameters were synthesized by simple laser ablation of sintered target in air. The dopant concentration has been restricted within the solid solubility limit of 1 mol%. The Sm 3+ ion substitution in ZnO matrix results in the formation of inter-band levels by the characteristic 4f level of Sm 3+ in the forbidden gap of ZnO. Thus, when the micro-spheres are excited with 488 nm, four major visible emissions associated with Sm 3+ f − f transitions namely, transitions from 4 G 5/2 to its low-lying multiplets of 6 H J (J = 5/2, 7/2, 9/2 and 11/2), are obtained. These emissions are coupled to the WGMs of the Sm 3+ :ZnO micro-cavity resulting in sharp resonances in the visible region. Interestingly, the resonances are found to be lasing above lower pumping powers. The Q-factor obtained is of the order of 10 3 for spheres of size ranging 1.8-10.2 µm. The best Q-factor obtained is 3744 for 561.61 nm peak (FWHM 0.15 nm) from 8 µm sphere. These results would find a place in visible range lasing and sensor applications.

Red-Emitting Cr3+ on α-Al2O3:Cr Spheres Obtained in Seconds Using Laser Processing

“…The main fabrication approaches typically involve the melting of glass materials or the sol-gel process [26]. Other methods to produce crystalline spheres of different sizes (from nano to some millimeters) have been reported and include laser ablation [25,[28][29][30], spray pyrolysis [31,32], microfluidic synthesis strategies [33], hydrolysis-precipitation methods [34], hydrothermal [35], and even other laser sintering approaches [36].…”

Microwave-assisted in situ laser dye incorporation into high sensitivity whispering gallery mode microresonators

“…Optical microresonators are highly sensitive to the surrounding environment. Changes of physical properties such as temperature [1,2], humidity [3], electric field strength [4], or others [5,6] can be detected via changes in the refractive index on a variety of materials such as polymers, metal oxides or other semiconductors [7][8][9][10][11][12][13][14][15]. Also nanoparticle decorated resonators have been realised, exploiting plasmonic coupling [16].…”