Charge deformation and orbital hybridization: intrinsic mechanisms on tunable chromaticity of Y3Al5O12:Ce3+ luminescence by doping Gd3+ for warm white LEDs

Abstract

The deficiency of Y3Al5O12:Ce (YAG:Ce) luminescence in red component can be compensated by doping Gd3+, thus lead to it being widely used for packaging warm white light-emitting diode devices. This article presents a systematic study on the photoluminescence properties, crystal structures and electronic band structures of (Y1−xGdx)3Al5O12: Ce3+ using powerful experimental techniques of thermally stimulated luminescence, X-ray diffraction, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and ultraviolet photoelectron spectra (UPS) of the valence band, assisted with theoretical calculations on the band structure, density of states (DOS), and charge deformation density (CDD). A new interpretation from the viewpoint of compression deformation of electron cloud in a rigid structure by combining orbital hybridization with solid-state energy band theory together is put forward to illustrate the intrinsic mechanisms that cause the emission spectral shift, thermal quenching, and luminescence intensity decrease of YAG: Ce upon substitution of Y3+ by Gd3+, which are out of the explanation of the classic configuration coordinate model. The results indicate that in a rigid structure, the charge deformation provides an efficient way to tune chromaticity, but the band gaps and crystal defects must be controlled by comprehensively accounting for luminescence thermal stability and efficiency.

Effects of local structure of Ce3+ ions on luminescent properties of Y3Al5O12:Ce nanoparticles

“…Belén et al 23 studied the interplay between the Ce Y and Y Al -Al Y in YAG by using the first-principles calculations and found that the presence of Y Al -Al Y could cause a strongly anisotropic expansion of the atomistic structure around the Ce Y impurities and decrease the effective ligand-field splitting of the 5 d 1 manifold, leading to the blue-shifts the two lowest Ce 3+ 4f–5d transitions. Although the photoluminescence properties of Ce 3+ ions in garnet structure were investigated24, the detailed relationship between the photoluminescence properties and the local structures as well as the distributions of activators in Ce 3+ -doped YAG phosphors have been rarely studied experimentally.…”

Luminescence Saturation in Inorganic Phosphors under High Flux of Photon Excitation

“…The excitation absorbed by the phosphor is excited from the 4f 1 ( 2 F 7/2 ) to 4f 0 5d 1 excited state, and the excited photons are emitted in the form of light and heat, respectively, with radiative recombination and non-radiative recombination. [27][28][29][30] According to the energy transitions above, the photons absorbed from the LD are excited from the 4f 1 (2F 7/2 ) ground state to 4f 0 5d 1 excited state and the excited photons are then relaxed to the 4f 1 (2F 7/2 ) ground state. The relaxation is divided into two types: non-radiative recombination (dotted line in Fig.…”

Quantum-mechanical modeling of spatial and band structure of Y3Al5O12 scintillation crystal

“…В результате анализа рассчитанных плотностей электронных состояний были получены значения ширины запрещенной зоны в трех случаях: без оптимизации, с оптимизацией в рамках PM6 и PM7. Полученные результаты сравнивались с известным экспериментальным значением ширины запре-щенной зоны для YAG, равным по разным данным [1,3] порядка 7 эВ. Наиболее точный результат, 5,5 эВ, достигнут с использованием пространственной структуры, полученной в рамках метода PM7.…”

“…Гранаты -широко известный класс кристаллов, используемый в качестве люминофоров, твердо-тельных лазеров или сцинтилляторов [1]. Сцинтиллятор -это объект, преобразующий энергию ионизи-рующего излучения в фотоны оптического диапазона, которые могут быть легко зарегистрированы со-временными приемниками и обработаны электронной аппаратурой.…”