1.      Introduction

 In recent past, rare earth doped phosphors have been extensively investigated due to the optical properties they poses. The existence of this property is 4f-4f transition possible in rare earth ions (1). Yttrium Oxide is one of the hosts used in luminescence, has the significant ability to be used in optical applications due to sufficiently high band gap and significantly low phonon energy. Being oxides it is thermally and chemically stable compound. All these abilities reduces the possibilities of non-radiative relaxation procedure hence results in increase of luminescence efficiency (2). In this chapter, we dealt with Er³⁺ as dopant and Ho³⁺ as co-dopant. The photoluminescence spectra of Er³⁺ exhibit strong green and red emission. These emission are suitable for various applications like laser, medical imaging and many more. On the other hand, Holmium also functions like activator and emits efficient green and red colour which is again suitable for display and sensing applications (3). When Er³⁺ is co-doped with Ho³⁺, the energy transfer takes place from Er³⁺ to Ho³⁺ results in up-conversion luminescence. Here Ho³⁺ also acts as sensitizer therefore, we seen enhance in luminescence intensity. This introduces tenability within the visible region spectra (4). These energy transfer interactions enables Y₂O₃:Er³⁺, Ho³⁺ phosphors to be a suitable candidate for various applications like Infrared (IR)-to-visible upconversion, white light LED component and Medical imaging (5). doping with La³⁺ can switch the dominant upconversion emission from red to green in Y₂O₃ doped with Yb³⁺ and, Er³⁺ matrix, thus provides a new way to get the visible light. Ho³⁺, Yb³⁺ doped Y₂O₃ thin films has also been reported where sensitivity dependence of intensity of PL emission, PL emission dependency on substrate temperature were also examined (6). In summary, Y₂O₃ co-doped with Er³⁺ and Ho³⁺ offers a versatile luminescent platform. Its favorable host properties, along with the tunability afforded by energy transfer and co-doping strategies, support its utility in advanced photonic, sensing, and imaging applications (7).

2. Materials and Methods

2.1 Structural analysis

In order to confirm the formation of expected phases in the material prepared, XRD pattern of the one of the samples (Y₂O₃: 1.5 mol% of Er³⁺ and 2.5 mol% of Ho³⁺) was observed. The observed pattern was matched using Crystal Impact Match 3! Software where it expressed the strong resemblance with COD card No. 96-153-7883 with figure of merit of 0.96. The discussed COD card belongs to Y₂O₃ with cubic lattice type having I a -3 (206) space group. To visualize the similarities between the observed and calculated XRD pattern, a comparative graph (Figure 1) is plotted. The calculated pattern was obtained from the crystallographic information file (cif) corresponding to the COD card No. 96-153-7883. From Figure 1, it is clear that there is a significant resemblance between the observed and calculated XRD pattern of material considered (8).

Figure 1: Comparison between observed and standard XRD pattern.

2.2 Morphological analysis

In order to analysis the surface morphology of the samples prepared. The sample with optimum PL intensity (Er – 1.5 mol% and Ho – 2.5 mol %) was considered.

Figure 2: Progressive SEM Analysis Revealing Morphological Details of Y₂O₃:Er³⁺/Ho³⁺ Phosphor at Increasing Resolutions (5k–60k) Figure 3: Photoluminescence Emission Spectra of Y₂O₃: Er³⁺ (1.5 mol %), Ho³⁺ when excited at 980 nm IR source)

Figure 3 provides the Photoluminescence (PL) Emission spectra of Y₂O₃: Er³⁺ (1.5 mol %), and varying concentrations (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol %) of Ho³⁺. The PL emission was monitored at an excitation wavelength of 980 nm. It may clear be seen that the PL emission intensity increased with increasing concentration of Ho³⁺, it was maximum when concentration Ho³⁺ was 2.5 mol% and beyond that (3.0 mol%) the intensity decreased. PL concentration quenching may be regarded as the possible reason for this. It is also noticed that there are 05 peaks centered at 409 nm, 455 nm, 491 nm, 524 nm and 657 nm. Out of these 05 peaks 02 peaks centered at 524 nm and 657 nm were prominent and are attributed to ⁵F₃ ® ⁵I₈ and ⁵F₅ ® ⁵I₈ respectively. The transition is shown in Figure 4.

Figure 4: Possible transition in Ho³⁺ activator

2.      Conclusion

Samples of Y₂O₃ doped with 1.5 mol% of Er³⁺ and various concentration (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol %) of Ho³⁺ was prepared. XRD spectrum of a sample that provided optimum PL emission was observed. The observed spectrum matched significantly with COD (Crystallographic Open Database) card No. 96-153-7883. This provides us the information that it belongs to Cubic lattice family with I a -3 (206) space group. The Photoluminescence emission spectra of the samples were recorded at an excitation of 980 nm and exhibited 05 peaks centered at 409 nm, 455 nm, 491 nm, 524 nm and 657 nm. Out of these 05 peaks 02 peaks centered at 524 nm and 657 nm were prominent and are attributed to ⁵F₃ ® ⁵I₈ and ⁵F₅ ® ⁵I₈ respectively.