Production of BN nanostructures by pulsed laser ablation in liquids: Influence of the applied Nd:YAG harmonics on the structural, optical and photoluminescence properties

In this work, three different Nd:YAG laser radiations (lambda = 1064, 532, and 355 nm) were analyzed to obtain BN particles using pulsed laser ablation in liquids (PLALs). The effect of the laser energy in two reaction media (deionized water and acetone) during BN synthesis was analyzed through their structural, optical and photoluminescence properties. XRD patterns show the main reflections of h-BN and the existence of impurity phases that corresponds to c-BN or e-BN structures. The nanosecond laser energy is enough to transform h-BN hybridization from sp(2) to sp(3) and form new phases. The crystallite sizes (CS) of the h-BN particles grown in deionized water are between 66.4-68.8 nm for the three applied Nd:YAG harmonics. Similar CS were observed in colloidal BN particles fabricated in acetone (66.6-67.8 nm). The combination of the laser energy and reaction media modifies the BN particles morphology from platelets randomly oriented (D.W.) to melting-like structures (acetone). Size and melting degree are modified with the laser energy due to the capacity for plasma confinement of each reaction medium. Raman spectroscopy showed two vibrational modes dependent on the laser wavelength confirming that e-BN and c-BN phases coexist in the h-BN matrix. The formation of these secondary phases and morphological features are responsible of the differences in the optical properties. BN nanocrystals growth in D.W. like colloidal medium can act as UV shielding. Photoluminescence of BN structures (1064 nm) is observed in the range of 300-550 nm with a maximum emission at 3.26 eV. Due to the high structure disorder, the BN structures showed a broad emission with an intense luminescence that remain fairly constant after 48 h; resulting in blue luminescence character.