Band assignments	Relative intensity	Wavenumber [cm⁻¹] BTSO: 0.5Er1Yb	Wavenumber [cm⁻¹] BTSO: 0.5Er0.75Yb0	Wavenumber [cm⁻¹] BTSO: 0.5Er
M-O stretching vibration	Broad	584	553	561
${CO}_{3}^{2 -}$ bending vibration	Weak	852	852	854
${CO}_{3}^{2 -}$ bending vibration	Weak	1043	1041	1031
${CO}_{3}^{2 -}$ stretching vibration	Weak	1386	1380	1388
${CO}_{3}^{2 -}$ stretching vibration	Weak	1434	1434	1434
O-H bending vibration	Medium	1629	1629	1629
C-H stretching vibrations (CH₂group)	Weak	2857	2857	2856
C-H stretching vibrations (CH₃ group)	Medium	2925	2925	2923
O-H stretching vibration	Very broad	3438	3432	3442