Structural, Thermal and Spectral features of Ho3+doped Borophosphate Glasses for Photonic and Laser Materials Applications

Abstract

Glasses samples containing Ho3+ in Ytterbium Zinc Lithium Cadmium Potassium niobate Borophosphate Glasses (25-x)P2O5: 10ZnO: 10Li2O: 10CdO: 10K2O: 10Nb2O5:10Y2O3 :15B2O3 :xHo2O3 (where x=1, 1.5,2 mol %) have been prepared by melt-quenching method. The amorphous nature of the prepared glass samples was confirmed by X-ray diffraction. DTA curve was analysed to evaluate the glass transition temperature, crystallization temperature and melting temperature. Optical absorption, Excitation and fluorescence spectra were recorded at room temperature for all glass samples. Judd-Ofelt intensity parameters ?? (?=2, 4 and 6) are evaluated from the intensities of various absorption bands of optical absorption spectra. Using these intensity parameters various radiative properties like spontaneous emission probability (A), branching ratio (?), radiative life time (?R) and stimulated emission cross–section ( ?p) of various emission lines have been evaluated.

Introduction

This study focuses on the preparation and characterization of Ho³?-doped ytterbium zinc lithium cadmium potassium niobate borophosphate (YZLCPNBP) glasses for potential laser and photonic applications. Rare-earth-doped glasses are widely used in optical fiber amplifiers, up-conversion lasers, waveguide lasers, electroluminescent devices, and memory devices due to their excellent optical properties. Borate-based glasses are particularly attractive because of their high transparency, high refractive index, low dispersion, good thermal stability, and strong mechanical properties.

Objectives

The main aim of the work was to investigate the:

• Optical absorption spectra,
• Excitation spectra,
• Fluorescence spectra,
• Differential Thermal Analysis (DTA) of Ho³?-doped borophosphate glasses.

The study also employed Judd–Ofelt (J–O) theory to determine important spectroscopic and laser parameters such as:

• Radiative transition probabilities (A),
• Branching ratios (β),
• Radiative lifetimes (τR),
• Stimulated emission cross-sections (σp).

Glass Preparation

Three glass compositions containing 1.0, 1.5, and 2.0 mol% Ho?O? were synthesized using the melt-quenching technique.

• Raw materials included P?O?, ZnO, Li?O, CdO, K?O, Nb?O?, Y?O?, B?O?, and Ho?O?.
• The mixtures were melted at 1060°C for 2 hours.
• The molten glass was quenched in a preheated stainless-steel mold.
• Samples were annealed at 250°C for 2 hours to remove internal stresses.
• The resulting glasses were transparent and possessed good optical quality.

Theoretical Background

The optical properties were analyzed using:

1. Oscillator strength calculations derived from absorption spectra.
2. Judd–Ofelt theory, which provides intensity parameters (Ω?, Ω?, Ω?) describing the local environment around Ho³? ions.
3. Calculations of radiative properties including:
   • Spontaneous emission probability,
   • Fluorescence branching ratio,
   • Radiative lifetime,
   • Stimulated emission cross-section.
4. Nephelauxetic ratio (β') and bonding parameter (b¹?²) to study the nature of Ho–O bonding in the glass matrix.

Results

1. XRD Analysis

• The X-ray diffraction pattern showed no sharp crystalline peaks.
• Only a broad diffuse hump was observed.
• This confirms that the prepared Ho³?-doped glasses are amorphous in nature.

2. Structural and Spectroscopic Characteristics

• The borophosphate glass network provides a suitable host for Ho³? ions.
• Li?O improves optical, electrical, and mechanical properties.
• ZnO enhances glass-forming ability and suppresses crystallization.
• Ho³? ions exhibit high solubility and favorable optical characteristics in the glass matrix.

Conclusion

In the present study, the glass samples of composition (25-x)P2O5: 10ZnO: 10Li2O: 10CdO: 10K2O: 10Nb2O5:10Y2O3 :15B2O3:xHo2O3 (where x =1, 1.5and 2mol %) have been prepared by melt-quenching method. The large value of Balaji and Shankar parameters indicate that the prepared glass samples have good thermal stability. The value of stimulated emission cross-section (?p) is found to be maximum for the transition (5I7?5I8) for glass YZLCPNBP HO (1.0), suggesting that glass YZLCPNBP HO(1.0) is better compared to the other two glass systems YZLCPNBP HO(1.5) and YZLCPNBP HO (2.0). The large stimulated emission cross section in borate glasses suggests the possibility of utilizing these systems as laser materials. The results show that the Ho3+ doped bismuth borate glasses could be potential candidates for Photonic and Laser Materials Applications.

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Copyright

Copyright © 2026 S. L. Meena. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.