Room temperature WGM resonances in the red spectral range from Ho3+ activated ZnO micro-spherical cavities

Abstract

Highly crystalline and smooth 1% Ho3+ doped ZnO microspheres with diameters ranging from 0.5 to 15 μm were synthesized using laser ablation technique. Near band edge whispering gallery mode (WGM) resonances from Ho:ZnO microspheres with a single oscillation route in the UV range are observed with 355 nm excitation. Apart from the significantly enhanced visible WGM resonances associated with intrinsic oxygen vacancy defects by Ho3+ doping, the visible range WGM resonances associated with the Ho3+ 5F5 → 5I8 emission at 629–690 nm are also observed with a 488 nm excitation. The WGMs of Ho3+ f-f emission possess lower threshold and high Q-factor values.

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

“…The spheres obtained by this process will be of different sizes ranging from 0.5 µm to 25 µm, which gives an opportunity to explore the WGM emission property of spheres with different sizes in one time synthesis. More over, spheres obtained by laser ablation tend to have very smooth surface (with an average roughness [28] (r a ) ∼ 2 nm) which is one of the major requirements for WGM cavity lasing because rougher surface causes scattering leading to confinement loss [22]. In addition, we adopt this technique because of the challenge in effective doping of bigger Sm 3+ ion (1.075 Å) as a substitute to smaller Zn 2+ (0.74 Å) in ZnO lattice.…”

“…However, there are not many studies on the visible range WGM lasing in ZnO. To our best knowledge, the visible WGM studies so far in ZnO have been focused on the native defect related WGMs emissions [15][16][17][18][19][20][21][22][23][24][25][26] or WGMs of dye coated ZnO micro-cavity [27] except our recent report on achieving WGM lasing from Ho:ZnO micro-spheres in the red spectral range [28]. We have reported Ho 3+ -4f originated WGMs at 629-690 nm from Ho:ZnO micro-spheres of different sizes and their lasing properties [28].…”

“…To our best knowledge, the visible WGM studies so far in ZnO have been focused on the native defect related WGMs emissions [15][16][17][18][19][20][21][22][23][24][25][26] or WGMs of dye coated ZnO micro-cavity [27] except our recent report on achieving WGM lasing from Ho:ZnO micro-spheres in the red spectral range [28]. We have reported Ho 3+ -4f originated WGMs at 629-690 nm from Ho:ZnO micro-spheres of different sizes and their lasing properties [28]. This motivated us to continue working for efficient WGM lasing from ZnO in the different regions of visible spectrum by doping with other rare earth (RE) ions.…”