Spectroscopic properties of neodymium ions in LiYO2 monocrystals

Abstract

The growth of LiYO2 and its structure are discussed. The absorption and luminescence spectra of Nd3+ in LiYO2 monocrystals are recorded at 4.2, 50, 77, and 300 K in the region from 250 to 2500 nm. The Nd3+ ion energy level diagram is constructed on the basis of the spectral data. Theoretical calculations of the intrinsic crystal field parameters (on the “Minsk‐22” computer) make possible to draw some conclusions about the coordination and the symmetry of the activator center. The calculated Nd3+ ion energy levels are in good agreement with the experimental ones. The colour center formation under γ‐irradiation is also investigated.

Phase Transition‐Driven Highly Sensitive, NIR–NIR Band‐Shape Luminescent Thermometer Based on LiYO2:Nd3+

“…Consequently, the local point symmetry of the Y 3+ ions substituted by the lanthanide (Ln 3+ ) dopant ions changes from the C 2 to D 2d . [27,[33][34][35] Since the local point symmetry determines the strength of crystal field splitting of the multiplets of the luminescent ions into Stark sublevels, the observed temperature-driven phase transition significantly modifies the optical properties of the LiYO 2 :Nd 3+ phosphor. To trace and understand this structural phase transition the XRD patterns were measured as a function of temperature (Figure 1b).…”

“…[ 28,29 ] Therefore, here, LiYO 2 :Nd 3+ nanocrystals have been synthesized for which the temperature increase above ≈290 K induces a structural change from monoclinic ( P 2 1 / c , Z = 4) to tetragonal ( I 4 1 / amd , Z = 4) and thus a change in the point symmetry of the crystallographic site of Y 3+ (occupied by the luminescent Nd 3+ ions) from C 2 to D 2d . [ 30–33 ] This symmetry change clearly affects the energy of the Stark levels of the 4 I J mutiplets (Figure S3, Supporting Information) and thus significantly changes the shape of the excitation and emission spectra (Figures S4 and S5, Supporting Information). The unique configuration of the energy levels of the Nd 3+ ions enables to achieve three luminescent bands at ≈ 880 nm ( 4 F 3/2 → 4 I 9/2 , 1 st optical window), 1060 nm ( 4 F 3/2 → 4 I 11/2 ; 2 nd optical window) and 1350 nm ( 4 F 3/2 → 4 I 13/2 , 2nd optical window), respectively, upon optical excitation at 808 nm (electron transition 4 I 9/2 → 4 F 5/2 , 4 S 3/2 ; 1st optical window).…”

“…[28,29] Therefore, here, LiYO 2 :Nd 3+ nanocrystals have been synthesized for which the temperature increase above ≈290 K induces a structural change from monoclinic (P2 1 /c, Z = 4) to tetragonal (I4 1 /amd, Z = 4) and thus a change in the point symmetry of the crystallographic site of Y 3+ (occupied by the luminescent Nd 3+ ions) from C 2 to D 2d . [30][31][32][33] This symmetry change clearly affects the energy of the Stark levels of the 4 I J mutiplets (Figure S3, Supporting Information) Almost all existing luminescent thermometers rely on the temperaturedependent processes such as multi-phonon relaxation and phonon-assisted energy transfers, thermal population, or coupling between energy levels of ground and excited states of luminescent species (lanthanides, transition metals, quantum dots, fluorescent molecules, etc.). Although such phenomena are in principle suitable for straightforward calibration, aiming to offer high temperature sensitivity, high temperature resolution and the widest possible temperature sensitivity range, their performance is often dependent on the excitation intensity or sample dispersive properties and often suffers from insufficient brightness, which further becomes dimmer at increased temperatures.…”