Characteristics of neodymium modified borate crystals and glasses grown via polycrystalline seed mediation

Abstract

A series of glass samples with composition (90-x)Li2B4O7+10Nb2O5+xNd2O3, where x = 1, 5, 10, 15, and 20 mol% were prepared by the melt-quenching technique. For polycrystal seed preparation as well as crystal growth process, 1 mol% of Nd2O3 was chosen. Nd2O3 was used as a modifier to investigate the impact on the physical, structural, and optical properties of the glasses and crystals. Polycrystal seed as well as platinum wire and lithium niobate single crystal seed were used to grow crystals by Czochralski technique. The growth and growth mechanism of the crystals were studied. The glass samples and crystals were subjected to various characterisation techniques and the physical, structural, and optical properties were determined. XRD pattern confirmed the amorphous nature of the glass system while several peaks corresponded to the phases of LiNbO3, LiNb3O8, Li2B4O7, and Nd(BO2)3 were recorded for heat-treated glass (polycrystal). The microstructural of the samples (glass ? polycrystal) showed that these crystallites grew, further suggesting that the nucleation and growth process were responsible for the development of this kind of microstructure. The optimum growth conditions of pulling rates and rotation speeds were 0.2–1.5 mmh-1 and 5–7 rpm, respectively. To stabilise the growth rate and achieve a good growth interface, the temperature gradient was gently optimised. FTIR spectra exhibited four vibration bands around 700, 800–1200, 1200–1600, and 3200–3600 cm-1 assigned to the bending of B–O–Nd, B–O stretching of tetrahedral [BO4] units, stretching relaxation of B–O in [BO3] units, and stretching of O–H group in both NdLNB crystal and glass system. The UV–Vis spectra showed ten absorption peaks and the transition at 4G5/2 (583 nm) was the most prominent. As the concentration of Nd3+ ions for glass system increased, both optical band gap and Urbach energies decreased. Additionally, the optical band gap of NdLNB crystal was significantly lower than that of NdLNB glass which were 2.84 and 3.75 eV, respectively. The Judd-Ofelt intensity parameters of all the glass samples followed the trend of O6 > O4 > O2 except for 5NdLNB glass, which followed the trend of O4 > O6 > O2 which similar to NdLNB crystal. The radiative lifetime of the glass system increased with increasing Nd3+ concentration. Meanwhile, radiative lifetime for NdLNB crystal was slightly higher than for NdLNB glass. Luminescence spectra showed two prominent infrared emissions at 903 and 1059 nm which were due to 4F3/2?4I9/2 and 4F3/2?4I11/2 transitions, respectively while NdLNB crystal exhibited four emissions at 883, 943, 1064, and 1115 nm with the same transition. SHG tests for both NdLNB crystal and NdLNB glass recorded an emission peak at 532 and 529.5 nm, respectively. The achieved results promise the use of these optimised glasses and crystals in frequency conversion, nonlinear optical application, and laser production. The new approach of using the polycrystal seed to grow a crystal with modified properties from its own glass-forming melt was also successful.