Influence of NiO on phase transformations and optical properties of ZnO–Al2O3–SiO2 glass–ceramics nucleated by TiO2 and ZrO2. Part II. Optical absorption and luminescence

In situ evolution of Ni environment in magnesium aluminosilicate glasses and glass–ceramics–Influence of ZrO2 and TiO2 nucleating agents

“…Model compounds were measured to obtain reference spectra for the different Ni coordinations: NiCr 2 O 4 for tetrahedral coordination ( [4] Ni 2 þ ); KNiPO 4 and Ni 2 P 2 O 7 for five-fold coordination ( [5] Ni 2 þ ); CaNiSi 2 O 6 , Ni(OH) 2 , NiO and NiAl 2 O 4 spinel for octahedral coordination ( [6] Ni 2 þ ) [9,10].…”

“…The transitions are dipole-forbidden in octahedral O h symmetry and partly allowed in non-centrosymmetric sites (tetrahedral T d symmetry). These selection rules are responsible for the difference observed on the pre-edge intensity of the crystalline references (Table 2), with normalized intensity values of 0.049 and 0.018 for [4] Ni 2 þ and [6] Ni 2 þ sites, respectively. For the glasses, the pre-edge intensities (feature A in Fig.…”

“…Among TM ions, tetrahedrally coordinated Cr 4 þ [1,2], octahedrally coordinated Cr 3 þ [3,4] Bi ions in different valences and coordination states and octahedrally coordinated Ni 2 þ [5][6][7][8] can have broad emission bandwidths (typically4200 nm) in the near-infrared range from 1-1.7 μm. Ni 2 þ ions are mostly encountered in trigonal bipyramid and tetrahedral sites in oxide glasses [9][10][11], so that their emission efficiency is weak or non-existing in glasses compared to crystals.…”

“…This explains the growing interest to develop transparent nanophase spinel glass-ceramics, which can be easily prepared, with low cost for mass production, compared to single crystalline counterparts [13]. Spinel crystallization has been mainly considered in aluminosilicate systems (SiO 2 -Al 2 O 3 -Li 2 O-ZnO-MgO) [1,5,[13][14][15][16][17][18][19][20][21][22][23][24][25], demonstrating the possibility to obtain a broad IR luminescence due to Ni 2 þ in spinel phase [6][7][8][21][22][23][24][26][27][28][29].…”

“…However, it has a relatively strong influence in the observed crystallization sequence. Ni 2 þ ions do not enter the Zr-containing crystalline phase of ZrO 2 or ZrTiO 4 but a Ni 2 þ coordination change from the fivefold coordinated sites, with a small amount of tetrahedral sites in parent glasses, to [6] Ni 2 þ and [4] Ni 2 þ sites in spinel (in glasses nucleated by ZrO 2 and/or TiO 2 ) or in β-quartz solid solutions (in glasses nucleated by ZrO 2 ) has been found. …”